Andromeda Galaxy: Difference between revisions

Latest revision as of 15:13, 18 November 2025

Template:Short description Script error: No such module "redirect hatnote". Template:Good article Template:Use dmy dates Script error: No such module "Infobox".Template:Template otherScript error: No such module "Check for unknown parameters".

The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D₂₅ isophotal diameter of about Template:Convert^[1] and is approximately Template:Convert from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.^[1]

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at Template:Convert. The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy was more massive than the Milky Way by a margin of some 25% to 50%.^[2] However, this has been called into question by early-21st-century studies indicating a possibly lower mass for the Andromeda Galaxy^[2] and a higher mass for the Milky Way.^[3]^[4] The Andromeda Galaxy has a diameter of about Template:Cvt, making it the largest member of the Local Group of galaxies in terms of extension.^[4]

The Milky Way and Andromeda galaxies have about a 50% chance of colliding with each other in the next 10 billion years,^[5] merging to potentially form a giant elliptical galaxy^[6] or a large lenticular galaxy.^[7]

With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects,^[8] and is visible to the naked eye from Earth on moonless nights,^[9] even when viewed from areas with moderate light pollution.^[1]

Observation history

File:Auv0175.png

Oldest surviving depiction of the Andromeda (dots at the tip of the mouth of the lower fish), by Al-Sufi in The Book of Fixed Stars (from around 964 CE) in a manuscript from 1009 to 1010 CE^[10]^[11]

The Andromeda Galaxy is visible to the naked eye in dark skies.^[12] It has been speculated that the Babylonian constellation of the Rainbow, Mul Dingir Tir-an-na, may have referred to M31.^[13] Around the year 964 CE, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy in his Book of Fixed Stars as a "nebulous smear" or "small cloud".^[14] This was the first historical reference to the Andromeda Galaxy and the earliest known reference to a galaxy other than the Milky Way.^[15] Star charts of that period labeled it as the Little Cloud.^[16] In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations.^[17] John Flamsteed cataloged it as 33 Andromedae.^[18] Pierre Louis Maupertuis conjectured in 1745 that the blurry spot was an island universe.^[19] Charles Messier cataloged Andromeda as object M31 in 1764 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda.^[9] He believed Andromeda to be the nearest of all the "great nebulae," and based on the color and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius, or roughly Template:Cvt.^[20]

In 1850, William Parsons, 3rd Earl of Rosse, made a drawing of Andromeda's spiral structure.^[21]Template:Better source needed

In 1864, William Huggins noted that the spectrum of Andromeda differed from that of a gaseous nebula.^[22] The spectrum of Andromeda displays a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. Andromeda's spectrum is very similar to the spectra of individual stars, and from this, it was deduced that Andromeda has a stellar nature. In 1885, a supernova (known as S Andromedae) was seen in Andromeda, the only one ever observed in that galaxy.^[23] At the time, it was called "Nova 1885"^[24]—the difference between "novae" in the modern sense and supernovae was not yet known. Andromeda was considered to be a nearby object, and it was not realized that the "nova" was much brighter than ordinary novae.Script error: No such module "Unsubst".

File:Andromeda Nebula - Isaac Roberts, 29 December 1888 (cropped).jpg

The earliest known photograph of the Great Andromeda "Nebula" (with M110 to the upper right), by Isaac Roberts (29 December 1888)

In 1888, Isaac Roberts took one of the first photographs of Andromeda, which was still commonly thought to be a nebula within the Milky Way galaxy. Roberts mistook Andromeda and similar "spiral nebulae" as star systems being formed.^[25]^[26]

In 1912, Vesto Slipher used spectroscopy to measure the radial velocity of Andromeda with respect to the Solar System—the largest velocity yet measured, at Template:Cvt.^[27]

"Island universes" hypothesis

File:Andromeda constellation map.svg

Location of the Andromeda Galaxy (M31) in the Andromeda constellation

As early as 1755, the German philosopher Immanuel Kant proposed the hypothesis that the Milky Way is only one of many galaxies in his book Universal Natural History and Theory of the Heavens. Arguing that a structure like the Milky Way would look like a circular nebula viewed from above and like an ellipsoid if viewed from an angle, he concluded that the observed elliptical nebulae like Andromeda, which could not be explained otherwise at the time, were indeed galaxies similar to the Milky Way, not nebulae, as Andromeda was commonly believed to be.^[28]

In 1917, Heber Curtis observed a nova within Andromeda. After searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred elsewhere in the sky. As a result, he was able to come up with a distance estimate of Template:Convert. Although this estimate is about fivefold lower than the best estimates now available, it was the first known estimate of the distance to Andromeda that was correct to within an order of magnitude (i.e., to within a factor of ten of the current estimates, which place the distance around 2.5 million light-years^[29]^[30]^[31]^[32]). Curtis became a proponent of the so-called "island universes" hypothesis: that spiral nebulae were actually independent galaxies.^[33]

In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe.^[34] To support his claim that the Great Andromeda Nebula is, in fact, an external galaxy, Curtis also noted the appearance of dark lanes within Andromeda that resembled the dust clouds in the Milky Way galaxy, as well as historical observations of the Andromeda Galaxy's significant Doppler shift. In 1922, Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside the Milky Way at a distance of about Template:Cvt.^[23] Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of Andromeda. These were made using the Template:Convert Hooker telescope, and they enabled the distance of the Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within the Milky Way galaxy, but an entirely separate galaxy located a significant distance from the Milky Way.^[34]

In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy. Baade identified two distinct populations of stars based on their metallicity, naming the young, high-velocity stars in the disk Type I and the older, red stars in the bulge Type II.^[35] This nomenclature was subsequently adopted for stars within the Milky Way and elsewhere. (The existence of two distinct populations had been noted earlier by Jan Oort.)^[35] Baade also discovered that there were two types of Cepheid variable stars, which resulted in doubling the distance estimate to Andromeda, as well as the remainder of the universe.^[36]

In 1950, radio emissions from the Andromeda Galaxy were detected by Robert Hanbury Brown and Cyril Hazard at the Jodrell Bank Observatory.^[37]^[38] The first radio maps of the galaxy were made in the 1950s by John Baldwin and collaborators at the Cambridge Radio Astronomy Group.^[39] The core of the Andromeda Galaxy is called 2C 56 in the 2C radio astronomy catalog.

In 1959 rapid rotation of the semi-stellar nucleus of M31 was discovered by Andre Lallemand, M. Duschene and Merle Walker^[40] at the Lick Observatory, using the 120-inch telescope, coudé Spectrograph, and Lallemand electronographic camera. They estimated the mass of the nucleus to be about 1.3 x 10⁷ solar masses. The second example of this phenomenon was found in 1961 in the nucleus of M32 by M.F Walker^[41] at the Lick Observatory, using the same equipment as used for the discovery of the nucleus of M31. He estimated the nuclear mass to be between 0.8 and 1 x 10⁷ solar masses. Such rotation is now considered to be evidence of the existence of supermassive black holes in the nuclei of these galaxies.

21st century

File:Largest Mosaic of Andromeda by Hubble jan 16 2025-extra details.jpg

Largest Mosaic of Andromeda by Hubble with details: (a) Clusters of bright blue stars embedded within the galaxy, background galaxies seen much farther away, and photo-bombing by a couple bright foreground stars that are actually inside our Milky Way; (b) NGC 206 the most conspicuous star cloud in Andromeda; (c) A young cluster of blue newborn stars; (d) The satellite galaxy M32, that may be the residual core of a galaxy that once collided with Andromeda; (e) Dark dust lanes across myriad stars.^[42]

In 2009, an occurrence of microlensing—a phenomenon caused by the deflection of light by a massive object—may have led to the first discovery of a planet in the Andromeda Galaxy.^[43]

In 2020, observations of linearly polarized radio emission with the Westerbork Synthesis Radio Telescope, the Effelsberg 100-m Radio Telescope, and the Very Large Array revealed ordered magnetic fields aligned along the "10-kpc ring" of gas and star formation.^[44]

In 2023, amateur astronomers Marcel Drechsler, Xavier Strottner and Yann Sainty announced the discovery of a huge, oxygen-rich emission nebula just south of M31, near the bright star 35 And. This nebula, now classified as SDSO-1, is exceedingly faint, requiring dozens of hours of exposure time minimum to detect, and appears to only emit in oxygen-III.^[45] Deep studies of the surrounding regions showed no signs of similarly bright oxygen nebulae near M31, nor any sign of connecting hydrogen filaments to SDSO-1, suggesting a high oxygen-hydrogen ratio. Current research suggests SDSO-1 is extragalactic in nature, specifically caused by interaction between the Milky Way's and M31's circumgalactic halos, although more research is needed to fully understand this object.^[46] A later study using spectroscopy found the nebula to be in the Milky Way.^[47] One study found the nebula to be a bow shock of a ghost planetary nebula around the binary EG Andromedae.^[48]

In 2025, NASA published a huge mosaic made by the Hubble Space Telescope, assembled from approximately 600 separate overlapping fields of view taken over 10 years of Hubble observation. Hubble resolves an estimated 200 million stars that are hotter than the Sun, but still a fraction of the galaxy's total estimated stellar population.

General

The estimated distance of the Andromeda Galaxy from our own was doubled in 1953 when it was discovered that there is a second, dimmer type of Cepheid variable star. In the 1990s, measurements of both standard red giants as well as red clump stars from the Hipparcos satellite measurements were used to calibrate the Cepheid distances.^[49]^[50]

Formation and history

File:Andromeda Galaxy 560mm FL.jpg

Processed image of the Andromeda Galaxy, with enhancement of H-alpha to highlight its star-forming regions

A major merger occurred 2 to 3 billion years ago at the Andromeda location, involving two galaxies with a mass ratio of approximately 4.^[51]^[52]

The discovery of a recent merger in the Andromeda galaxy was first based on interpreting its anomalous age-velocity dispersion relation,^[53] as well as the fact that 2 billion years ago, star formation throughout Andromeda's disk was much more active than today.^[54]

Modeling^[51] of this violent collision shows that it has formed most of the galaxy's (metal-rich) galactic halo, including the Giant Stream,^[55] and also the extended thick disk, the young age thin disk, and the static 10 kpc ring. During this epoch, its rate of star formation would have been very high, to the point of becoming a luminous infrared galaxy for roughly 100 million years. Modeling also recovers the bulge profile, the large bar, and the overall halo density profile.

Andromeda and the Triangulum Galaxy (M33) might have had a very close passage 2–4 billion years ago, but it seems unlikely from the last measurements from the Hubble Space Telescope.^[56]

Distance estimate

File:Milky Way and Andromeda in space, to scale.jpg

Illustration showing both the size of each galaxy and the distance between the two galaxies, to scale

At least four distinct techniques have been used to estimate distances from Earth to the Andromeda Galaxy. In 2003, using the infrared surface brightness fluctuations (I-SBF) and adjusting for the new period-luminosity value and a metallicity correction of −0.2 mag dex⁻¹ in (O/H), an estimate of Template:Convert was derived. A 2004 Cepheid variable method estimated the distance to be 2.51 ± 0.13 million light-years (770 ± 40 kpc).^[29]^[30]

In 2005, an eclipsing binary star was discovered in the Andromeda Galaxy. The binaryTemplate:Efn is made up of two hot blue stars of types O and B. By studying the eclipses of the stars, astronomers were able to measure their sizes. Knowing the sizes and temperatures of the stars, they were able to measure their absolute magnitude. When the visual and absolute magnitudes are known, the distance to the star can be calculated. The stars lie at a distance of Template:Convert and the whole Andromeda Galaxy at about Template:Convert.^[31] This new value is in excellent agreement with the previous, independent Cepheid-based distance value. The TRGB method was also used in 2005 giving a distance of Template:Convert.^[32] Averaged together, these distance estimates give a value of Template:Convert.Template:Efn

Mass estimates

File:Hubble Finds Giant Halo Around the Andromeda Galaxy.jpg

Giant halo around Andromeda Galaxy^[57]

Until 2018, mass estimates for the Andromeda Galaxy's halo (including dark matter) gave a value of approximately Template:Solar mass,^[58] compared to Template:Solar mass for the Milky Way. This contradicted even earlier measurements that seemed to indicate that the Andromeda Galaxy and Milky Way are almost equal in mass. In 2018, the earlier measurements for equality of mass were re-established by radio results as approximately Template:Solar mass.^[59]^[60]^[61]^[62] In 2006, the Andromeda Galaxy's spheroid was determined to have a higher stellar density than that of the Milky Way,^[63] and its galactic stellar disk was estimated at twice the diameter of that of the Milky Way.^[64] The total mass of the Andromeda Galaxy is estimated to be between Template:Solar mass^[59] and Template:Solar mass.^[65]^[66] The stellar mass of M31 is Template:Solar mass, with 30% of that mass in the central bulge, 56% in the disk, and the remaining 14% in the stellar halo.^[67] The radio results (similar mass to the Milky Way Galaxy) should be taken as likeliest as of 2018, although clearly, this matter is still under active investigation by several research groups worldwide.

As of 2019, current calculations based on escape velocity and dynamical mass measurements put the Andromeda Galaxy at Template:Solar mass,^[68] which is only half of the Milky Way's newer mass, calculated in 2019 at Template:Solar mass.^[69]^[70]^[71]

In addition to stars, the Andromeda Galaxy's interstellar medium contains at least Template:Solar mass^[72] in the form of neutral hydrogen, at least Template:Solar mass as molecular hydrogen (within its innermost 10 kiloparsecs), and Template:Solar mass of dust.^[73]

The Andromeda Galaxy is surrounded by a massive halo of hot gas that is estimated to contain half the mass of the stars in the galaxy. The nearly invisible halo stretches about a million light-years from its host galaxy, halfway to our Milky Way Galaxy. Simulations of galaxies indicate the halo formed at the same time as the Andromeda Galaxy. The halo is enriched in elements heavier than hydrogen and helium, formed from supernovae, and its properties are those expected for a galaxy that lies in the "green valley" of the Galaxy color-magnitude diagram (see below). Supernovae erupt in the Andromeda Galaxy's star-filled disk and eject these heavier elements into space. Over the Andromeda Galaxy's lifetime, nearly half of the heavy elements made by its stars have been ejected far beyond the galaxy's 200,000-light-year-diameter stellar disk.^[74]^[75]^[76]^[77]

Luminosity estimates

The estimated luminosity of the Andromeda Galaxy, Template:Solar luminosity, is about 25% higher than that of our own galaxy.^[78]^[79] However, the galaxy has a high inclination as seen from Earth, and its interstellar dust absorbs an unknown amount of light, so it is difficult to estimate its actual brightness and other authors have given other values for the luminosity of the Andromeda Galaxy (some authors even propose it is the second-brightest galaxy within a radius of 10 megaparsecs of the Milky Way, after the Sombrero Galaxy,^[80] with an absolute magnitude of around −22.21Template:Efn or close^[81]).

An estimation done with the help of Spitzer Space Telescope published in 2010 suggests an absolute magnitude (in the blue) of −20.89 (that with a color index of +0.63 translates to an absolute visual magnitude of −21.52,Template:Efn compared to −20.9 for the Milky Way), and a total luminosity in that wavelength of Template:Solar luminosity.^[82]

The rate of star formation in the Milky Way is much higher, with the Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of novae in the Milky Way is also double that of the Andromeda Galaxy.^[83] This suggests that the latter once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation.^[78] Should this continue, the luminosity of the Milky Way may eventually overtake that of the Andromeda Galaxy.

According to recent studies, the Andromeda Galaxy lies in what is known in the galaxy color–magnitude diagram as the "green valley", a region populated by galaxies like the Milky Way in transition from the "blue cloud" (galaxies actively forming new stars) to the "red sequence" (galaxies that lack star formation). Star formation activity in green valley galaxies is slowing as they run out of star-forming gas in the interstellar medium. In simulated galaxies with similar properties to the Andromeda Galaxy, star formation is expected to extinguish within about five billion years, even accounting for the expected, short-term increase in the rate of star formation due to the collision between the Andromeda Galaxy and the Milky Way.^[84]

Structure

Template:Wide image

File:A Swift Tour of M31.ogv

A narrated tour of the Andromeda Galaxy, made by NASA's Swift satellite team

Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies.^[85] However, infrared data from the 2MASS survey and the Spitzer Space Telescope showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar major axis oriented 55 degrees anti-clockwise from the disc major axis.^[86]

There are various methods used in astronomy in defining the size of a galaxy, and each method can yield different results concerning one another. The most commonly employed is the D₂₅ standard, the isophote where the photometric brightness of a galaxy in the B-band (445 nm wavelength of light, in the blue part of the visible spectrum) reaches 25 mag/arcsec².^[87] The Third Reference Catalogue of Bright Galaxies (RC3) used this standard for Andromeda in 1991, yielding an isophotal diameter of Template:Convert at a distance of 2.5 million light-years.^[1] An earlier estimate from 1981 gave a diameter for Andromeda at Template:Convert.^[88]

A study in 2005 by the Keck telescopes shows the existence of a tenuous sprinkle of stars, or galactic halo, extending outward from the galaxy.^[64] The stars in this halo behave differently from the ones in Andromeda's main galactic disc, where they show rather disorganized orbital motions as opposed to the stars in the main disc having more orderly orbits and uniform velocities of 200 km/s.^[64] This diffuse halo extends outwards away from Andromeda's main disc with the diameter of Template:Convert.^[64]

The galaxy is inclined an estimated 77° relative to Earth (where an angle of 90° would be edge-on). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk.^[89] A possible cause of such a warp could be gravitational interaction with the satellite galaxies near the Andromeda Galaxy. The Galaxy M33 could be responsible for some warp in Andromeda's arms, though more precise distances and radial velocities are required.Script error: No such module "Unsubst".

Spectroscopic studies have provided detailed measurements of the rotational velocity of the Andromeda Galaxy as a function of radial distance from the core. The rotational velocity has a maximum value of Template:Cvt at Template:Convert from the core, and it has its minimum possibly as low as Template:Cvt at Template:Convert from the core. Further out, rotational velocity rises out to a radius of Template:Convert, where it reaches a peak of Template:Cvt. The velocities slowly decline beyond that distance, dropping to around Template:Cvt at Template:Convert. These velocity measurements imply a concentrated mass of about Template:Solar mass in the nucleus. The total mass of the galaxy increases linearly out to Template:Convert, then more slowly beyond that radius.^[90]

The spiral arms of the Andromeda Galaxy are outlined by a series of HII regions, first studied in great detail by Walter Baade and described by him as resembling "beads on a string". His studies show two spiral arms that appear to be tightly wound, although they are more widely spaced than in our galaxy.^[91] His descriptions of the spiral structure, as each arm crosses the major axis of the Andromeda Galaxy, are as follows^[92]^§pp1062^[93]^§pp92:

Baade's spiral arms of M31
Arms (N=cross M31's major axis at north, S=cross M31's major axis at south)	Distance from center (arcminutes) (N/S)	Distance from the center (kpc) (N/S)	Notes
N1/S1	3.4/1.7	0.7/0.4	Dust arms with no OB associations of HII regions
N2/S2	8.0/10.0	1.7/2.1	Dust arms with some OB associations
N3/S3	25/30	5.3/6.3	As per N2/S2, but with some HII regions too
N4/S4	50/47	11/9.9	Large numbers of OB associations, HII regions, and little dust
N5/S5	70/66	15/14	As per N4/S4 but much fainter
N6/S6	91/95	19/20	Loose OB associations. No dust is visible.
N7/S7	110/116	23/24	As per N6/S6 but fainter and inconspicuous

File:Andromeda galaxy Ssc2005-20a1.jpg

Image of the Andromeda Galaxy taken by Spitzer in infrared, 24 micrometres (Credit: NASA/JPL–Caltech/Karl D. Gordon, University of Arizona)

Since the Andromeda Galaxy is seen close to edge-on, it is difficult to study its spiral structure. Rectified images of the galaxy seem to show a fairly normal spiral galaxy, exhibiting two continuous trailing arms that are separated from each other by a minimum of about Template:Convert and that can be followed outward from a distance of roughly Template:Convert from the core. Alternative spiral structures have been proposed such as a single spiral arm^[94] or a flocculent^[95] pattern of long, filamentary, and thick spiral arms.^[85]^[96]

The most likely cause of the distortions of the spiral pattern is thought to be interaction with galaxy satellites M32 and M110.^[97] This can be seen by the displacement of the neutral hydrogen clouds from the stars.^[98]

In 1998, images from the European Space Agency's Infrared Space Observatory demonstrated that the overall form of the Andromeda Galaxy may be transitioning into a ring galaxy. The gas and dust within the galaxy are generally formed into several overlapping rings, with a particularly prominent ring formed at a radius of Template:Cvt from the core,^[99] nicknamed by some astronomers the ring of fire.^[100] This ring is hidden from visible light images of the galaxy because it is composed primarily of cold dust, and most of the star formation that is taking place in the Andromeda Galaxy is concentrated there.^[101]

Later studies with the help of the Spitzer Space Telescope showed how the Andromeda Galaxy's spiral structure in the infrared appears to be composed of two spiral arms that emerge from a central bar and continue beyond the large ring mentioned above. Those arms, however, are not continuous and have a segmented structure.^[97]

Close examination of the inner region of the Andromeda Galaxy with the same telescope also showed a smaller dust ring that is believed to have been caused by the interaction with M32 more than 200 million years ago. Simulations show that the smaller galaxy passed through the disk of the Andromeda Galaxy along the latter's polar axis. This collision stripped more than half the mass from the smaller M32 and created the ring structures in Andromeda.^[102] It is the co-existence of the long-known large ring-like feature in the gas of Messier 31, together with this newly discovered inner ring-like structure, offset from the barycenter, that suggested a nearly head-on collision with the satellite M32, a milder version of the Cartwheel encounter.^[103]

Studies of the extended halo of the Andromeda Galaxy show that it is roughly comparable to that of the Milky Way, with stars in the halo being generally "metal-poor", and increasingly so with greater distance.^[63] This evidence indicates that the two galaxies have followed similar evolutionary paths. They are likely to have accreted and assimilated about 100–200 low-mass galaxies during the past 12 billion years.^[104] The stars in the extended halos of the Andromeda Galaxy and the Milky Way may extend nearly one-third the distance separating the two galaxies.

Nucleus

File:M31 nucleus (labels).jpg

Hubble Space Telescope image of the Andromeda Galaxy core showing P1, P2 and P3, with P3 containing M31*. NASA/ESA photo

The Andromeda Galaxy is known to harbor a dense and compact star cluster at its very center, similar to the Milky Way galaxy. A large telescope creates a visual impression of a star embedded in the more diffuse surrounding bulge. In 1991, the Hubble Space Telescope was used to image the Andromeda Galaxy's inner nucleus. The nucleus consists of two concentrations separated by Template:Cvt. The brighter concentration, designated as P1, is offset from the center of the galaxy. The dimmer concentration, P2, falls at the true center of the galaxy and contains an embedded star cluster, called P3,^[105] containing many UV-bright A-stars and the supermassive black hole, called M31*.^[106]^[107] The black hole is classified as a low-luminosity AGN (LLAGN) and it was detected only in radio wavelengths and in x-rays.^[107] It was quiescent in 2004–2005, but it was highly variable in 2006–2007.^[106] An additional x-ray flare occurred in 2013.^[108] The mass of M31* was measured at 3–5 × 10⁷ Template:Solar mass in 1993,^[109] and at 1.1–2.3 × 10⁸ Template:Solar mass in 2005.^[105] The velocity dispersion of material around it is measured to be ≈ Template:Cvt.^[110]

It has been proposed that the observed double nucleus could be explained if P1 is the projection of a disk of stars in an eccentric orbit around the central black hole.^[111] The eccentricity is such that stars linger at the orbital apocenter, creating a concentration of stars. It has been postulated that such an eccentric disk could have been formed from the result of a previous black hole merger, where the release of gravitational waves could have "kicked" the stars into their current eccentric distribution.^[112] P2 also contains a compact disk of hot, spectral-class A stars. The A stars are not evident in redder filters, but in blue and ultraviolet light they dominate the nucleus, causing P2 to appear more prominent than P1.^[113]

While at the initial time of its discovery it was hypothesized that the brighter portion of the double nucleus is the remnant of a small galaxy "cannibalized" by the Andromeda Galaxy,^[114] this is no longer considered a viable explanation, largely because such a nucleus would have an exceedingly short lifetime due to tidal disruption by the central black hole. While this could be partially resolved if P1 had its own black hole to stabilize it, the distribution of stars in P1 does not suggest that there is a black hole at its center.^[111]

Discrete sources

File:PIA20061 - Andromeda in High-Energy X-rays, Figure 1.jpg

The Andromeda Galaxy in high-energy X-ray and ultraviolet light (released 5 January 2016)

Apparently, by late 1968, no X-rays had been detected from the Andromeda Galaxy.^[115] A balloon flight on 20 October 1970 set an upper limit for detectable hard X-rays from the Andromeda Galaxy.^[116] The Swift BAT all-sky survey successfully detected hard X-rays coming from a region centered 6 arcseconds away from the galaxy center. The emission above 25 keV was later found to be originating from a single source named 3XMM J004232.1+411314, and identified as a binary system where a compact object (a neutron star or a black hole) accretes matter from a star.^[117]

Multiple X-ray sources have since been detected in the Andromeda Galaxy, using observations from the European Space Agency's (ESA) XMM-Newton orbiting observatory. Robin Barnard et al. hypothesized that these are candidate black holes or neutron stars, which are heating the incoming gas to millions of kelvins and emitting X-rays. Neutron stars and black holes can be distinguished mainly by measuring their masses.^[118] An observation campaign of NuSTAR space mission identified 40 objects of this kind in the galaxy.^[119] In 2012, a microquasar, a radio burst emanating from a smaller black hole was detected in the Andromeda Galaxy. The progenitor black hole is located near the galactic center and has about 10 Template:Solar mass. It was discovered through data collected by the European Space Agency's XMM-Newton probe and was subsequently observed by NASA's Swift Gamma-Ray Burst Mission and Chandra X-Ray Observatory, the Very Large Array, and the Very Long Baseline Array. The microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy.^[120]

Globular clusters

File:Star cluster in the Andromeda galaxy.jpg

Star clusters in the Andromeda Galaxy^[121]

There are approximately 460 globular clusters associated with the Andromeda Galaxy.^[122] The most massive of these clusters, identified as Mayall II, nicknamed Globular One, has a greater luminosity than any other known globular cluster in the Local Group of galaxies.^[123] It contains several million stars and is about twice as luminous as Omega Centauri, the brightest known globular cluster in the Milky Way. Mayall II (also known as Globular One or G1) has several stellar populations and a structure too massive for an ordinary globular. As a result, some consider Mayall II to be the remnant core of a dwarf galaxy that was consumed by Andromeda in the distant past.^[124] The cluster with the greatest apparent brightness is G76 which is located in the southwest arm's eastern half.^[16] Another massive globular cluster, named 037-B327 (also known as Bol 37) and discovered in 2006 as is heavily reddened by the Andromeda Galaxy's interstellar dust, was thought to be more massive than Mayall II and the largest cluster of the Local Group;^[125] however, other studies have shown it is actually similar in properties to Mayall II.^[126]

Unlike the globular clusters of the Milky Way, which show a relatively low age dispersion, Andromeda Galaxy's globular clusters have a much larger range of ages: from systems as old as the galaxy itself to much younger systems, with ages between a few hundred million years to five billion years.^[127]

In 2005, astronomers discovered a completely new type of star cluster in the Andromeda Galaxy. The new-found clusters contain hundreds of thousands of stars, a similar number of stars that can be found in globular clusters. What distinguishes them from the globular clusters is that they are much larger—several hundred light-years across—and hundreds of times less dense. The distances between the stars are, therefore, much greater within the newly discovered extended clusters.^[128]

The most massive globular cluster in the Andromeda Galaxy, B023-G078, likely has a central intermediate black hole of almost 100,000 solar masses.^[129]

PA-99-N2 event and possible exoplanet in galaxy

Script error: No such module "Labelled list hatnote".

PA-99-N2 was a microlensing event detected in the Andromeda Galaxy in 1999. One of the explanations for this is the gravitational lensing of a red giant by a star with a mass between 0.02 and 3.6 times that of the Sun, which suggested that the star is likely orbited by a planet. This possible exoplanet would have a mass 6.34 times that of Jupiter. If finally confirmed, it would be the first ever found extragalactic planet. However, anomalies in the event were later found.^[130]

Nearby and satellite galaxies

Script error: No such module "Labelled list hatnote".

File:M31, the Andromeda Galaxy, Killarney Provincial Park Observatory.jpg

The Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center right below the galaxy)

Like the Milky Way, the Andromeda Galaxy has smaller satellite galaxies, consisting of over 20 known dwarf galaxies. The Andromeda Galaxy's dwarf galaxy population is very similar to the Milky Way's, but the galaxies are much more numerous.^[131] The best-known and most readily observed satellite galaxies are M32 and M110. Based on current evidence, it appears that M32 underwent a close encounter with the Andromeda Galaxy in the past. M32 may once have been a larger galaxy that had its stellar disk removed by M31 and underwent a sharp increase of star formation in the core region, which lasted until the relatively recent past.^[132]

M110 also appears to be interacting with the Andromeda Galaxy, and astronomers have found in the halo of the latter a stream of metal-rich stars that appear to have been stripped from these satellite galaxies.^[133] M110 does contain a dusty lane, which may indicate recent or ongoing star formation.^[134] M32 has a young stellar population as well.^[135]

The Triangulum Galaxy is a non-dwarf galaxy that lies 750,000 light-years from Andromeda. It is currently unknown whether it is a satellite of Andromeda.^[136]

In 2006, it was discovered that nine of the satellite galaxies lie in a plane that intersects the core of the Andromeda Galaxy; they are not randomly arranged as would be expected from independent interactions. This may indicate a common tidal origin for the satellites.^[137]

Collision with the Milky Way

Script error: No such module "Labelled list hatnote".

File:Collision paths of our Milky Way galaxy and the Andromeda galaxy.jpg

Illustration of the collision path between the Milky Way and Andromeda Galaxy

The Andromeda Galaxy is approaching the Milky Way at about Template:Convert per second.^[138] It has been measured approaching relative to the Sun at around Template:Cvt^[85] as the Sun orbits around the center of the galaxy at a speed of approximately Template:Cvt. This makes the Andromeda Galaxy one of about 100 observable blueshifted galaxies.^[139] Andromeda Galaxy's tangential or sideways velocity concerning the Milky Way is uncertain, but estimated to be smaller than the approaching velocity. After the sideways velocity was first measured, Andromeda was predicted to collide directly with the Milky Way in about 4 billion years.^[140] However, later calculations, including a higher sideways velocity measurement from the Gaia (spacecraft) and the effect of other Local Group galaxies found a much lower probability of a merger.^[5]

A likely outcome of the collision would be that the galaxies will merge to form a giant elliptical galaxy^[141] or possibly large disc galaxy.^[7] Such events are frequent among the galaxies in galaxy groups. The fate of Earth and the Solar System in the event of a collision is currently unknown. Before the galaxies merge, there is a small chance that the Solar System could be ejected from the Milky Way or join the Andromeda Galaxy.^[142]

Amateur observation

File:Moon over Andromeda (rotated).jpg

Superimposing picture showing sizes of the Moon and the Andromeda Galaxy as observed from Earth. Note that this photographic image shows much more of the galaxy's darker outer regions than an amateur observer is able to see.^[143]^[144]

Under most viewing conditions, the Andromeda Galaxy is one of the most distant objects that can be seen with the naked eye, due to its sheer size. (M33 and, for observers with exceptionally good vision, M81 can be seen under very dark skies.)^[145]^[146]^[147]^[148] The constellation of Andromeda, in which the galaxy is located, is usually found with the aid of the constellations Cassiopeia or Pegasus, which are usually easier to recognize at first glance. Andromeda is best seen during autumn nights in the Northern Hemisphere when it passes high overhead, reaching its highest point around midnight in October, and two hours earlier each successive month. In the early evening, it rises in the east in September and sets in the west in February.^[149] From the Southern Hemisphere the Andromeda Galaxy is visible between October and December, best viewed from as far north as possible. Binoculars can reveal some larger structures of the galaxy and its two brightest satellite galaxies, M32 and M110.^[150] An amateur telescope can reveal Andromeda's disk, some of its brightest globular clusters, dark dust lanes, and the large star cloud NGC 206.^[151]^[152]

Gallery

A visible light image of the Andromeda Galaxy and two satellite galaxies. Messier 32 is above the galactic nucleus and Messier 110 is at the bottom.

A visible light image of the Andromeda Galaxy and two satellite galaxies. Messier 32 is above the galactic nucleus and Messier 110 is at the bottom.

Notes

Template:Notelist

References

↑ ^a ^b ^c ^d Cite error: Invalid <ref> tag; no text was provided for refs named RC3
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Template:Cite thesis
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ PASP 1960, p.72
↑ 1962 Astrophysical Journal, 136, p.692
↑ Script error: No such module "citation/CS1".Template:Source-attribution
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b ^c ^d Script error: No such module "Citation/CS1". Also see the press release, Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b ^c Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".

Cite error: <ref> tag with name "trillion-stars" defined in <references> is not used in prior text.
Cite error: <ref> tag with name "SIMBAD-M31" defined in <references> is not used in prior text.
Cite error: <ref> tag with name "GAXEL" defined in <references> is not used in prior text.
Cite error: <ref> tag with name "adam" defined in <references> is not used in prior text.
Cite error: <ref> tag with name "GalaxyMass" defined in <references> is not used in prior text.

External links

Template:Sister project

Template:WikiSky
StarDate: M31 Fact Sheet
Messier 31, SEDS Messier pages
Astronomy Picture of the Day
- A Giant Globular Cluster in M31 1998 October 17.
- M31: The Andromeda Galaxy 2004 July 18.
- Andromeda Island Universe 2005 December 22.
- Andromeda Island Universe 2010 January 9.
- WISE Infrared Andromeda 2010 February 19.
- M31's angular size compared with full Moon 2013 August 1.
M31 and its central Nuclear Spiral
Amateur photography – M31
Globular Clusters in M31 at The Curdridge Observatory
First direct distance to Andromeda − Astronomy magazine article
Andromeda Galaxy at SolStation.com
Andromeda Galaxy at The Encyclopedia of Astrobiology, Astronomy, & Spaceflight
M31, the Andromeda Galaxy Template:Webarchive at NightSkyInfo.com
Script error: No such module "citation/CS1".
M31 (Apparent) Novae Page (IAU)
Multi-wavelength composite
Andromeda Project (crowd-source)
Script error: No such module "citation/CS1".
Hubble's High-Definition Panoramic View of the Andromeda Galaxy
Infrared-Radio Image of the Andromeda Galaxy (M31)
Creative Commons Astrophotography M31 Andromeda image download & processing guide Template:Webarchive
Script error: No such module "citation/CS1". "Guided Tour" interactive website.

Template:Andromeda galaxy Template:Messier objects Template:NGC objects:1-499 Template:Stars of Andromeda Template:Portal bar Template:Authority control Template:Sky

[RC3-1] Cite error: Invalid <ref> tag; no text was provided for refs named RC3

[Kafle2018-2] Script error: No such module "Citation/CS1".

[3] Script error: No such module "Citation/CS1".

[As-Now-4] Script error: No such module "citation/CS1".

[:2-5] Script error: No such module "Citation/CS1".

[milky-way-collide-6] Script error: No such module "citation/CS1".

[Ueda2014-7] Script error: No such module "Citation/CS1".

[Frommert_&_Kronberg_2007-8] Script error: No such module "citation/CS1".

[Messie-9] Script error: No such module "citation/CS1".

[w718-10] Script error: No such module "citation/CS1".

[j307-11] Script error: No such module "citation/CS1".

[firstName-12] Script error: No such module "citation/CS1".

[13] Script error: No such module "citation/CS1".

[Hafez-14] Template:Cite thesis

[15] Script error: No such module "citation/CS1".

[NSOG-16] Script error: No such module "citation/CS1".

[Aati-17] Script error: No such module "citation/CS1".

[18] Script error: No such module "Citation/CS1".

[Kant-19] Script error: No such module "citation/CS1".

[Herschel_1785-20] Script error: No such module "Citation/CS1".

[21] Script error: No such module "Citation/CS1".

[Huggins_&_Miller_1864-22] Script error: No such module "Citation/CS1".

[Öpik_1922-23] Script error: No such module "Citation/CS1".

[Backhouse_1888-24] Script error: No such module "Citation/CS1".

[NebPix-25] Script error: No such module "Citation/CS1".

[sciPho-26] Script error: No such module "citation/CS1".

[Slipher_1913-27] Script error: No such module "Citation/CS1".

[28] Script error: No such module "citation/CS1".

[Karachentsevetal2006-29] Script error: No such module "Citation/CS1".

[karachentsevetal2004-30] Script error: No such module "Citation/CS1".

[Ribas2005-31] Script error: No such module "Citation/CS1".

[McConnachieetal2005-32] Script error: No such module "Citation/CS1".

[Curtis_1988-33] Script error: No such module "Citation/CS1".

[Hubble_1929-34] Script error: No such module "Citation/CS1".

[Baade_1944-35] Script error: No such module "Citation/CS1".

[Gribbin_2001-36] Script error: No such module "citation/CS1".

[Brown_&_Hazard_1950-37] Script error: No such module "Citation/CS1".

[Brown_&_Hazard_1951-38] Script error: No such module "Citation/CS1".

[van_der_Kruit_&_Allen_1976-39] Script error: No such module "Citation/CS1".

[40] PASP 1960, p.72

[41] 1962 Astrophysical Journal, 136, p.692

[42] Script error: No such module "citation/CS1".Template:Source-attribution

[Ingrosso_2009-43] Script error: No such module "Citation/CS1".

[Beck_2020-44] Script error: No such module "Citation/CS1".

[45] Script error: No such module "citation/CS1".

[46] Script error: No such module "Citation/CS1".

[Lumbreras-Calle2024-47] Script error: No such module "citation/CS1".

[Ogle2025-48] Script error: No such module "citation/CS1".

[Holland_1998-49] Script error: No such module "Citation/CS1".

[Stanek_&_Garnavich_1998-50] Script error: No such module "Citation/CS1".

[Hammer_et_al._2018-51] Script error: No such module "Citation/CS1".

[D'Souza_and_Bell-52] Script error: No such module "Citation/CS1".

[Dorman_et_al._2014-53] Script error: No such module "Citation/CS1".

[Williams_et_al._2015-54] Script error: No such module "Citation/CS1".

[Ibata_et_al._2001-55] Script error: No such module "Citation/CS1".

[Patel_et_al._2017-56] Script error: No such module "Citation/CS1".

[Hubble-halo-57] Script error: No such module "citation/CS1".

[Jorge_Peñarrubia2014-58] Script error: No such module "Citation/CS1".

[Kafle_et_al._2018-59] Script error: No such module "Citation/CS1".

[Need4Speed-1-60] Script error: No such module "Citation/CS1".

[cosmic-61] Script error: No such module "citation/CS1".

[Space.com-62] Script error: No such module "citation/CS1".

[Kalirai_et_al_2006-63] Script error: No such module "Citation/CS1".

[Chapman_et_al_2006-64] Script error: No such module "Citation/CS1". Also see the press release, Script error: No such module "citation/CS1".

[Barmby_2006-65] Script error: No such module "Citation/CS1".

[Barmby2007-66] Script error: No such module "Citation/CS1".

[Tamm2012-67] Script error: No such module "Citation/CS1".

[Need4Speed-68] Script error: No such module "Citation/CS1".

[daily-69] Script error: No such module "citation/CS1".

[SA-20190308-70] Script error: No such module "citation/CS1".

[ARX-20190208-71] Script error: No such module "Citation/CS1".

[BraunThilkerWalterbosCorbelli2009-72] Script error: No such module "Citation/CS1".

[Andromedandust-73] Script error: No such module "Citation/CS1".

[Hubble-halo-a-74] Script error: No such module "citation/CS1".

[Massive-75] Script error: No such module "citation/CS1".

[Evidence-76] Script error: No such module "Citation/CS1".

[HaloFind-77] Script error: No such module "citation/CS1".

[vdb-78] Script error: No such module "Citation/CS1".

[Moskvitch_2010-79] Script error: No such module "citation/CS1".

[Karachentsev2004-80] Script error: No such module "Citation/CS1".

[McCall2014-81] Script error: No such module "Citation/CS1".

[Tempel2010-82] Script error: No such module "Citation/CS1".

[Liller_&_Mayer_1987-83] Script error: No such module "Citation/CS1".

[MWAY-84] Script error: No such module "Citation/CS1".

[ned-85] Script error: No such module "citation/CS1".

[Beaton_2006-86] Script error: No such module "Citation/CS1".

[GalaxySize-87] Script error: No such module "citation/CS1".

[AtlasofAndromeda-88] Script error: No such module "citation/CS1".

[UC_Santa_Cruz_2001-89] Script error: No such module "citation/CS1".

[Rubin_&_Ford_1970-90] Script error: No such module "Citation/CS1".

[Arp_1964-91] Script error: No such module "Citation/CS1".

[Bergh1991-92] Script error: No such module "Citation/CS1".

[Hodge1966-93] Script error: No such module "citation/CS1".

[Simien1978-94] Script error: No such module "Citation/CS1".

[Haas2000-95] Script error: No such module "Citation/CS1".

[Walterbos1988-96] Script error: No such module "Citation/CS1".

[Gordon2006-97] Script error: No such module "Citation/CS1".

[Braun_1991-98] Script error: No such module "Citation/CS1".

[ESA_1998-10-14-99] Script error: No such module "citation/CS1".

[M31youngclusters-100] Script error: No such module "citation/CS1".

[Andromedan10kpcring-101] Script error: No such module "Citation/CS1".

[Harvard-Smithsonian_2006-10-18-102] Script error: No such module "citation/CS1".

[Block2006-103] Script error: No such module "Citation/CS1".

[Bullock_&_Johnston_2005-104] Script error: No such module "Citation/CS1".

[Bender_et_al_2005-105] Script error: No such module "Citation/CS1".

[:0-106] Script error: No such module "Citation/CS1".

[:1-107] Script error: No such module "Citation/CS1".

[108] Script error: No such module "Citation/CS1".

[Lauer-109] Script error: No such module "Citation/CS1".

[Gebhardt_et_al_2000-110] Script error: No such module "Citation/CS1".

[Tremaine_1995-111] Script error: No such module "Citation/CS1".

[112] Script error: No such module "Citation/CS1".

[hubblesite_1993-07-20-113] Script error: No such module "citation/CS1".

[Schewe_&_Stein_1993-114] Script error: No such module "citation/CS1".

[Fujimoto_et_al_1969-115] Script error: No such module "Citation/CS1".

[Peterson_1973-116] Script error: No such module "citation/CS1".

[Marelli_et_al._2017-117] Script error: No such module "Citation/CS1".

[Barnard_Kolb_&_Osborne_2005-118] Script error: No such module "citation/CS1".

[And-Scand-119] Script error: No such module "citation/CS1".

[prostak-2012-120] Script error: No such module "citation/CS1".

[And-Clustr-121] Script error: No such module "citation/CS1".

[Barmby_&_Huchra_2001-122] Script error: No such module "Citation/CS1".

[hubblesite_1996-04-24-123] Script error: No such module "citation/CS1".

[Meylan_et_al_2001-124] Script error: No such module "Citation/CS1".

[SuperStr-125] Script error: No such module "Citation/CS1".

[Cohen06-126] Script error: No such module "Citation/CS1".

[Formations-127] Script error: No such module "Citation/CS1".

[Huxor_et_al_2005-128] Script error: No such module "Citation/CS1".

[central_black_hole-129] Script error: No such module "Citation/CS1".

[Better_needed-130] Script error: No such module "Citation/CS1".

[131] Script error: No such module "Citation/CS1".

[Bekki_et_al_2001-132] Script error: No such module "Citation/CS1".

[Ibata_et_al_2001-133] Script error: No such module "Citation/CS1".

[Young_2000-134] Script error: No such module "Citation/CS1".

[Rudenko-135] Script error: No such module "Citation/CS1".

[136] Script error: No such module "citation/CS1".

[Koch_&_Grebel_2006-137] Script error: No such module "Citation/CS1".

[nature-138] Script error: No such module "Citation/CS1".

[Answers-139] Script error: No such module "citation/CS1".

[Sohn-140] Script error: No such module "Citation/CS1".

[Cox_&_Loeb_2008-141] Script error: No such module "Citation/CS1".

[Cain_2007-142] Script error: No such module "citation/CS1".

[143] Script error: No such module "citation/CS1".

[144] Script error: No such module "citation/CS1".

[StarChild-145] Script error: No such module "citation/CS1".

[S&T-obs-146] Script error: No such module "citation/CS1".

[147] Script error: No such module "citation/CS1".

[148] Script error: No such module "citation/CS1".

[physics-149] Script error: No such module "citation/CS1".

[S&T-150] Script error: No such module "citation/CS1".

[Backyard-151] Script error: No such module "citation/CS1".

[A-Mall-152] Script error: No such module "citation/CS1".

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

[69]

[70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[79]

[80]

[81]

[82]

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

[92]

[93]

[94]

[95]

[96]

[97]

[98]

[99]

[100]

@@ Line 1: / Line 1: @@
 {{short description|Barred spiral galaxy in the Local Group}}
-{{Redirect|Galaxy M31|the smartphone|Samsung Galaxy M31|other uses|Andromeda (disambiguation){{!}}Andromeda}}
+{{Redirect|Galaxy M31|the smartphone|Samsung Galaxy M31|other uses|Andromeda (disambiguation){{!}}Andromeda (disambiguation)}}
 {{Good article}}
 {{Use dmy dates|date=August 2024}}
 {{Infobox galaxy
-| name = Andromeda Galaxy
+| name                 = Andromeda Galaxy
-| image = M31-Andromede-16-09-2023-Hamois.jpg
+| image                = Andromeda Galaxy 2025.png
-| caption = A visible light image of the Andromeda Galaxy and two satellite galaxies. [[Messier 32]] is above the galactic nucleus and [[Messier 110]] is at the bottom.
+| caption              = Andromeda Galaxy and its two satellite galaxies. [[Messier 32]] above and [[Messier 110]] below.
-| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
+| epoch                = [[Epoch (astronomy)#Julian years and J2000|J2000]]
-| pronounce = {{IPAc-en|æ|n|ˈ|d|r|ɒ|m|ᵻ|d|ə}}
+| pronounce            = {{IPAc-en|æ|n|ˈ|d|r|ɒ|m|ᵻ|d|ə}}
-| type = SA(s)b<ref name="ned"/>
+| type                 = SA(s)b<ref name="ned"/>
-| mass = {{val|1.5|0.2|e=12|u=}}<ref name="GalaxyMass"/>
+| mass                 = {{val|1.5|0.2|e=12|u=}}<ref name="GalaxyMass"/>
-| size = {{cvt|46.56|kpc|ly|sigfig=3|lk=on}}<br/>(diameter; [[Galaxy#Isophotal diameter|D<sub>25</sub> isophote]])<ref name="ned"/><ref name=RC3>{{cite book |last1=De Vaucouleurs |first1=Gerard |last2=De Vaucouleurs |first2=Antoinette |last3=Corwin |first3=Herold G. | last4=Buta |first4=Ronald J. |last5=Paturel |first5=Georges | last6=Fouque |first6=Pascal |title=Third Reference Catalogue of Bright Galaxies |year=1991 |bibcode=1991rc3..book.....D}}</ref>{{efn|name=AndromedaHalo|This is the diameter as measured through the D<sub>25</sub> standard. The halo extends up to a distance of {{convert|67.45|kpc|ly}}.<ref name="Chapman et al 2006"/>}}
+| size                 = {{cvt|46.56|kpc|ly|sigfig=3|abbr=on|lk=on|disp=x|<br /><small>(|)</small>|order=flip}}<br />{{small|(''diameter; [[Galaxy#Isophotal diameter|D{{sub|25}} isophote]]'')}}<ref name="ned"/><ref name=RC3>{{cite book |last1=De Vaucouleurs |first1=Gerard |last2=De Vaucouleurs |first2=Antoinette |last3=Corwin |first3=Herold G. | last4=Buta |first4=Ronald J. |last5=Paturel |first5=Georges | last6=Fouque |first6=Pascal |title=Third Reference Catalogue of Bright Galaxies |year=1991 |bibcode=1991rc3..book.....D}}</ref>{{efn|name=AndromedaHalo|This is the diameter as measured through the D<sub>25</sub> standard. The halo extends up to a distance of {{convert|67.45|kpc|ly}}.<ref name="Chapman et al 2006"/>}}
-| stars = ~1&nbsp;trillion (10<sup>12</sup>)<!-- exponential value to disambiguate "trillion" --><ref name="trillion-stars"/>
+| h1_scale_length_pc   = ≥{{convert|100|kpc|ly|sigfig=3|abbr=on|lk=on|disp=x|<br /><small>(|)</small>}}<ref name=thilker>{{cite journal|last1=Thilker |first1=David A. |last2=Braun |first2=Robert |last3=Walterbos |first3=Ren A. M. |last4=Corbelli |first4=Edvige |last5=Lockman |first5=Felix J. |last6=Murphy |first6=Edward |last7=Maddalena |first7=Ronald |title=On the Continuing Formation of the Andromeda Galaxy: Detection of H i Clouds in the M31 Halo |journal=The Astrophysical Journal |date=2004 |volume=601 |issue=1 |pages=L39–L42 |doi=10.1086/381703 |arxiv=astro-ph/0311571 |bibcode=2004ApJ...601L..39T }}</ref>
-<!--| age = 5 to 9&nbsp;billion years<ref name="Moskvitch 2010"/>-->
+| stars                = ~1&nbsp;trillion (10<sup>12</sup>)<!-- exponential value to disambiguate "trillion" --><ref name="trillion-stars"/>
-| ra = {{RA|00|42|44.3}}<ref name="ned"/>
+<!--| age                  = 5 to 9&nbsp;billion years<ref name="Moskvitch 2010"/>-->
-| dec = {{DEC|+41|16|9}}<ref name="ned"/>
+| ra                   = {{RA|00|42|44.3}}<ref name="ned"/>
-| dist_ly = {{cvt|765|kpc|Mly|lk=on}}<ref name="adam"/>
+| dec                  = {{DEC|+41|16|9}}<ref name="ned"/>
-| z = z = −0.001004 (minus sign indicates [[blueshift]])<ref name="ned"/>
+| dist_ly              = {{cvt|765|kpc|Mly|lk=on}}<ref name="adam"/>
-| h_radial_v = −301 ± 1 km/s<ref name="Karachentsevetal2006"/>
+| z                    = z = −0.001004 (minus sign indicates [[blueshift]])<ref name="ned"/>
-| appmag_v = 3.44<ref name="SIMBAD-M31"/><ref name="GAXEL"/>
+| h_radial_v           = −301 ± 1 km/s<ref name="Karachentsevetal2006"/>
-| size_v = {{Val|3.167|×|1|u=degree}}<ref name="ned"/>
+| appmag_v             = 3.44<ref name="SIMBAD-M31"/><ref name="GAXEL"/>
-| constellation name = [[Andromeda (constellation)|Andromeda]]
+| size_v               = {{Val|3.167|×|1|u=degree}}<ref name="ned"/>
-| absmag_v = −21.5{{efn|name=blue mag}}<ref name="Ribas2005"/>
+| constellation name   = [[Andromeda (constellation)|Andromeda]]
-| names = [[Messier object|M]]31, [[New General Catalogue|NGC]] 224, [[Uppsala General Catalogue|UGC]] 454, [[Principal Galaxies Catalogue|PGC]] 2557, [[Second Cambridge Catalogue of Radio Sources|2C]] 56 (Core),<ref name="ned"/> CGCG 535-17, [[Morphological Catalogue of Galaxies|MCG]] +07-02-016, [[IRAS]] 00400+4059, [[2MASX]] J00424433+4116074, GC 116, h 50, Bode 3, Flamsteed 58, Hevelius 32, Ha 3.3, IRC +40013
+| absmag_v             = −21.5{{efn|name=blue mag}}<ref name="Ribas2005"/>
+| names                = [[Messier object|M]]31, [[New General Catalogue|NGC]] 224, [[Uppsala General Catalogue|UGC]] 454, [[Principal Galaxies Catalogue|PGC]] 2557, [[Second Cambridge Catalogue of Radio Sources|2C]] 56 (Core),<ref name="ned"/> CGCG 535-17, [[Morphological Catalogue of Galaxies|MCG]] +07-02-016, [[IRAS]] 00400+4059, [[2MASX]] J00424433+4116074, GC 116, h 50, Bode 3, Flamsteed 58, Hevelius 32, Ha 3.3, IRC +40013
 }}
@@ Line 30: / Line 31: @@
 The [[virial mass]] of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at {{convert|1|e12solar mass|kg|abbr=off|lk=on}}. The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy was more massive than the Milky Way by a margin of some 25% to 50%.<ref name="Kafle2018"/> However, this has been called into question by early-21st-century studies indicating a possibly lower mass for the Andromeda Galaxy<ref name="Kafle2018"/> and a higher mass for the Milky Way.<ref>{{cite journal |last1=López-Corredoira |first1=M. |last2=Prieto |first2=C. Allende |last3=Garzón |first3=F. |last4=Wang |first4=H. |last5=Liu |first5=C. |last6=Deng |first6=L. |date=1 April 2018 |title=Disk stars in the Milky Way detected beyond 25 kpc from its center |url=https://www.aanda.org/articles/aa/abs/2018/04/aa32880-18/aa32880-18.html |journal=Astronomy & Astrophysics |volume=612 |pages=L8 |arxiv=1804.03064 |bibcode=2018A&A...612L...8L |doi=10.1051/0004-6361/201832880 |via=aanda.org}}</ref><ref name="As-Now"/> The Andromeda Galaxy has a [[diameter]] of about {{cvt|46.56|kpc|ly|sigfig=3}}, making it the largest member of the [[Local Group]] of galaxies in terms of extension.<ref name="As-Now"/>
-The Milky Way and Andromeda galaxies are [[Andromeda–Milky Way collision|expected to collide with each other]] in around 4–5&nbsp;billion years,<ref name="Schiavi"/> merging to potentially form a giant [[elliptical galaxy]]<ref name="milky-way-collide"/> or a large [[lenticular galaxy]].<ref name="Ueda2014"/>
+The Milky Way and Andromeda galaxies have about a 50% chance of [[Andromeda–Milky Way collision|colliding with each other]] in the next 10&nbsp;billion years,<ref name=":2" /> merging to potentially form a giant [[elliptical galaxy]]<ref name="milky-way-collide"/> or a large [[lenticular galaxy]].<ref name="Ueda2014"/>
 With an [[apparent magnitude]] of 3.4, the Andromeda Galaxy is among the brightest of the [[Messier object]]s,<ref name="Frommert & Kronberg 2007"/> and is visible to the [[naked eye]] from Earth on moonless nights,<ref name="Messie"/> even when viewed from areas with moderate [[light pollution]].<ref name="RC3"/>
 == Observation history ==
-[[File:Auv0175.png|thumb|Oldest surviving depiction of the Andromeda (dots at the tip of the mouth of the lower), by [[Al-Sufi]] in ''[[The Book of Fixed Stars]]'' (from around 964 CE) in a manuscript from 1009–1010 CE<ref name="w718">{{cite web | title=Andromeda Galaxy al-Sufi | website=[[Ian Ridpath]] | url=http://www.ianridpath.com/startales/andromeda-alsufi.html | access-date=2024-11-22}}</ref><ref name="j307">{{cite web | title=The earliest image of another galaxy | website=Ivan Debono | date=2015-09-16 | url=http://www.idebono.eu/2015/09/16/the-earliest-image-of-another-galaxy/ | access-date=2024-11-22}}</ref>]]
+[[File:Auv0175.png|thumb|Oldest surviving depiction of the Andromeda (dots at the tip of the mouth of the lower fish), by [[Al-Sufi]] in ''[[The Book of Fixed Stars]]'' (from around 964 CE) in a manuscript from 1009 to 1010 CE<ref name="w718">{{cite web | title=Andromeda Galaxy al-Sufi | website=[[Ian Ridpath]] | url=http://www.ianridpath.com/startales/andromeda-alsufi.html | access-date=2024-11-22}}</ref><ref name="j307">{{cite web | title=The earliest image of another galaxy | website=Ivan Debono | date=2015-09-16 | url=http://www.idebono.eu/2015/09/16/the-earliest-image-of-another-galaxy/ | access-date=2024-11-22}}</ref>]]
-The Andromeda Galaxy is visible to the naked eye in dark skies.<ref name="firstName"/> Around the year 964 [[Common Era|CE]], the [[Greater Iran|Persian]] astronomer [[Abd al-Rahman al-Sufi]] described the Andromeda Galaxy in his ''[[Book of Fixed Stars]]'' as a "nebulous smear" or "small cloud".<ref name="Hafez"/> [[Star chart]]s of that period labeled it as the ''Little Cloud''.<ref name="NSOG"/> In 1612, the German astronomer [[Simon Marius]] gave an early description of the Andromeda Galaxy based on telescopic observations.<ref name="Aati"/> [[Pierre Louis Maupertuis]] conjectured in 1745 that the blurry spot was an island universe.<ref name="Kant"/> [[Charles Messier]] cataloged Andromeda as object M31 in 1764 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye. In 1785, the astronomer [[William Herschel]] noted a faint reddish hue in the core region of Andromeda.<ref name="Messie"/> He believed Andromeda to be the nearest of all the "great [[nebula]]e," and based on the color and magnitude of the [[nebula]], he incorrectly guessed that it was no more than 2,000 times the distance of [[Sirius]], or roughly {{cvt|18000|ly|kpc|lk=on}}.<ref name="Herschel 1785"/>
+The Andromeda Galaxy is visible to the naked eye in dark skies.<ref name="firstName"/> It has been speculated that the Babylonian constellation of the Rainbow, Mul Dingir Tir-an-na, may have referred to M31.<ref>{{Cite book |title=Babylonian Star-Lore: An Illustrated Guide to the Star-lore and Constellations of Ancient Babylonia |last=White |first=Gavin |publisher=Solaria Publications |year=2008 |location=London |page=165}}</ref> Around the year 964 [[Common Era|CE]], the [[Greater Iran|Persian]] astronomer [[Abd al-Rahman al-Sufi]] described the Andromeda Galaxy in his ''[[Book of Fixed Stars]]'' as a "nebulous smear" or "small cloud".<ref name="Hafez"/> This was the first historical reference to the Andromeda Galaxy and the earliest known reference to a galaxy other than the [[Milky Way]].<ref>{{Cite web |date=2023-12-09 |title=Updating stars and observing the Andromeda Galaxy |url=https://blog.sciencemuseum.org.uk/updating-stars-and-observing-the-andromeda-galaxy/ |access-date=2025-07-14 |website=Science Museum Blog |language=en-GB}}</ref> [[Star chart]]s of that period labeled it as the ''Little Cloud''.<ref name="NSOG"/> In 1612, the German astronomer [[Simon Marius]] gave an early description of the Andromeda Galaxy based on telescopic observations.<ref name="Aati"/> [[John Flamsteed]] cataloged it as [[Flamsteed designation|33 Andromedae]].<ref>{{cite journal | last=Wagman | first=M. | title=Flamsteed's Missing Stars | journal=Journal for the History of Astronomy | volume=18 | issue=3 | page=211 |date=August 1987 | bibcode=1987JHA....18..209W | doi=10.1177/002182868701800305| s2cid=118445625 }}</ref> [[Pierre Louis Maupertuis]] conjectured in 1745 that the blurry spot was an island universe.<ref name="Kant"/> [[Charles Messier]] cataloged Andromeda as object M31 in 1764 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye. In 1785, the astronomer [[William Herschel]] noted a faint reddish hue in the core region of Andromeda.<ref name="Messie"/> He believed Andromeda to be the nearest of all the "great [[nebula]]e," and based on the color and magnitude of the [[nebula]], he incorrectly guessed that it was no more than 2,000 times the distance of [[Sirius]], or roughly {{cvt|18000|ly|kpc|lk=on}}.<ref name="Herschel 1785"/>
 In 1850, [[William Parsons, 3rd Earl of Rosse]], made a drawing of Andromeda's [[Spiral galaxy#Structure|spiral structure]].<!-- in doubt: Andromeda galaxy is _not_ listed here: http://articles.adsabs.harvard.edu/pdf/1991JHA....22..257D --><ref>{{Cite journal |last=Payne-Gaposchkin |first=Cecilia H. |year=1953 |title=Why do Galaxies have a Spiral Form? |journal=Scientific American |volume=189 |issue=3 |pages=89–99 |bibcode=1953SciAm.189c..89P |doi=10.1038/scientificamerican0953-89 |issn=0036-8733 |jstor=24944338 }}</ref>{{better source needed|date=January 2024}}
-In 1864, [[William Huggins]] noted that the [[spectrum]] of Andromeda differed from that of a gaseous nebula.<ref name="Huggins & Miller 1864"/> The spectrum of Andromeda displays a [[wikt:continuum|continuum]] of [[frequency|frequencies]], superimposed with dark [[spectral line|absorption lines]] that help identify the chemical composition of an object. Andromeda's spectrum is very similar to the spectra of individual stars, and from this, it was deduced that Andromeda has a stellar nature. In 1885, a [[supernova]] (known as [[SN 1885A|S Andromedae]]) was seen in Andromeda, the first and so far only one observed in that galaxy.<ref name="Öpik 1922"/> At the time, it was called "Nova 1885"<ref name="Backhouse 1888"/>—the difference between "[[novae]]" in the modern sense and supernovae was not yet known. Andromeda was considered to be a nearby object, and it was not realized that the "nova" was much brighter than ordinary novae.{{citation needed|date=October 2023}}
+In 1864, [[William Huggins]] noted that the [[spectrum]] of Andromeda differed from that of a gaseous nebula.<ref name="Huggins & Miller 1864"/> The spectrum of Andromeda displays a [[wikt:continuum|continuum]] of [[frequency|frequencies]], superimposed with dark [[spectral line|absorption lines]] that help identify the chemical composition of an object. Andromeda's spectrum is very similar to the spectra of individual stars, and from this, it was deduced that Andromeda has a stellar nature. In 1885, a [[supernova]] (known as [[SN 1885A|S Andromedae]]) was seen in Andromeda, the only one ever observed in that galaxy.<ref name="Öpik 1922"/> At the time, it was called "Nova 1885"<ref name="Backhouse 1888"/>—the difference between "[[novae]]" in the modern sense and supernovae was not yet known. Andromeda was considered to be a nearby object, and it was not realized that the "nova" was much brighter than ordinary novae.{{citation needed|date=October 2023}}
-[[File:Andromeda_Nebula_-_Isaac_Roberts,_29_December_1888 (cropped).jpg|thumb|The earliest known photograph of the Great Andromeda "Nebula" (with [[Messier 110|M110]] to the upper right), by [[Isaac Roberts]] (29 December 1888)]]
+[[File:Andromeda Nebula - Isaac Roberts, 29 December 1888 (cropped).jpg|thumb|The earliest known photograph of the Great Andromeda "Nebula" (with [[Messier 110|M110]] to the upper right), by [[Isaac Roberts]] (29 December 1888)]]
-In 1888, [[Isaac Roberts]] took one of the first photographs of Andromeda, which was still commonly thought to be a nebula within our galaxy. Roberts mistook Andromeda and similar "spiral nebulae" as [[protoplanetary disc|star systems being formed]].<ref name="NebPix"/><ref name="sciPho"/>
+In 1888, [[Isaac Roberts]] took one of the first photographs of Andromeda, which was still commonly thought to be a nebula within the Milky Way galaxy. Roberts mistook Andromeda and similar "spiral nebulae" as [[protoplanetary disc|star systems being formed]].<ref name="NebPix"/><ref name="sciPho"/>
 In 1912, [[Vesto Slipher]] used [[spectroscopy]] to measure the [[radial velocity]] of Andromeda with respect to the [[Solar System]]—the largest velocity yet measured, at {{cvt|300|km/s}}.<ref name="Slipher 1913"/>
 === "Island universes" hypothesis ===
-[[File:Andromeda_constellation_map.svg|thumb|Location of the Andromeda Galaxy (M31) in the Andromeda constellation]]
+[[File:Andromeda constellation map.svg|thumb|Location of the Andromeda Galaxy (M31) in the Andromeda constellation]]
 As early as 1755, the German philosopher [[Immanuel Kant]] proposed the hypothesis that the Milky Way is only one of many galaxies in his book ''[[Universal Natural History and Theory of the Heavens]]''. Arguing that a structure like the Milky Way would look like a circular nebula viewed from above and like an [[Elliptical galaxy|ellipsoid]] if viewed from an angle, he concluded that the observed elliptical nebulae like Andromeda, which could not be explained otherwise at the time, were indeed galaxies similar to the Milky Way, not nebulae, as Andromeda was commonly believed to be.<ref>{{cite web |title=Seite:Allgemeine Naturgeschichte und Theorie des Himmels.djvu/41 – Wikisource |url=https://de.wikisource.org/wiki/Seite:Allgemeine_Naturgeschichte_und_Theorie_des_Himmels.djvu/41?useskin=vector |website=de.wikisource.org |language=de}}</ref>
 In 1917, [[Heber Doust Curtis|Heber Curtis]] observed a [[nova]] within Andromeda. After searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 [[Magnitude (astronomy)|magnitudes]] fainter than those that occurred elsewhere in the sky. As a result, he was able to come up with a distance estimate of {{convert|500000|ly|e9AU|abbr=unit}}. Although this estimate is about fivefold lower than the best estimates now available, it was the first known estimate of the distance to Andromeda that was correct to within an order of magnitude (i.e., to within a factor of ten of the current estimates, which place the distance around 2.5&nbsp;million light-years<ref name="Karachentsevetal2006"/><ref name="karachentsevetal2004"/><ref name="Ribas2005"/><ref name="McConnachieetal2005"/>). Curtis became a proponent of the so-called "island universes" hypothesis: that [[Spiral galaxy#Spiral nebula|spiral nebulae]] were actually independent galaxies.<ref name="Curtis 1988"/>
-In 1920, the [[Great Debate (astronomy)|Great Debate]] between [[Harlow Shapley]] and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the [[universe]].<ref name="Hubble 1929"/> To support his claim that the Great Andromeda Nebula is, in fact, an external galaxy, Curtis also noted the appearance of dark lanes within Andromeda that resembled the dust clouds in our own galaxy, as well as historical observations of the Andromeda Galaxy's significant [[Doppler shift]]. In 1922, [[Ernst Öpik]] presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside our galaxy at a distance of about {{cvt|450|kpc}}.<ref name="Öpik 1922"/> [[Edwin Hubble]] settled the debate in 1925 when he identified extragalactic [[Cepheid variable|Cepheid variable star]]s for the first time on astronomical photos of Andromeda. These were made using the {{convert|100|in|m|adj=on}} [[Hooker telescope]], and they enabled the distance of the Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our own galaxy, but an entirely separate galaxy located a significant distance from the Milky Way.<ref name="Hubble 1929"/>
+In 1920, the [[Great Debate (astronomy)|Great Debate]] between [[Harlow Shapley]] and Curtis took place concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the [[universe]].<ref name="Hubble 1929"/> To support his claim that the Great Andromeda Nebula is, in fact, an external galaxy, Curtis also noted the appearance of dark lanes within Andromeda that resembled the dust clouds in the Milky Way galaxy, as well as historical observations of the Andromeda Galaxy's significant [[Doppler shift]]. In 1922, [[Ernst Öpik]] presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside the Milky Way at a distance of about {{cvt|450|kpc}}.<ref name="Öpik 1922"/> [[Edwin Hubble]] settled the debate in 1925 when he identified extragalactic [[Cepheid variable|Cepheid variable star]]s for the first time on astronomical photos of Andromeda. These were made using the {{convert|100|in|m|adj=on}} [[Hooker telescope]], and they enabled the distance of the Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within the Milky Way galaxy, but an entirely separate galaxy located a significant distance from the Milky Way.<ref name="Hubble 1929"/>
 In 1943, [[Walter Baade]] was the first person to resolve stars in the central region of the Andromeda Galaxy. Baade identified two distinct populations of stars based on their [[metallicity]], naming the young, high-velocity stars in the disk [[Type-A star|Type I]] and the older, red stars in the bulge Type II.<ref name="Baade 1944"/> This nomenclature was subsequently adopted for stars within the Milky Way and elsewhere. (The existence of two distinct populations had been noted earlier by [[Jan Oort]].)<ref name="Baade 1944"/> Baade also discovered that there were two types of Cepheid variable stars, which resulted in doubling the distance estimate to Andromeda, as well as the remainder of the universe.<ref name="Gribbin 2001"/>
@@ Line 60: / Line 61: @@
 In 1950, radio [[Emission spectrum|emissions]] from the Andromeda Galaxy were detected by [[Robert Hanbury Brown]] and [[Cyril Hazard]] at the [[Jodrell Bank Observatory]].<ref name="Brown & Hazard 1950"/><ref name="Brown & Hazard 1951"/> The first [[radio astronomy|radio maps]] of the galaxy were made in the 1950s by [[John E. Baldwin|John Baldwin]] and collaborators at the [[Cavendish Astrophysics Group|Cambridge Radio Astronomy Group]].<ref name="van der Kruit & Allen 1976"/> The core of the Andromeda Galaxy is called 2C 56 in the [[Second Cambridge Catalogue of Radio Sources|2C]] radio astronomy catalog.
-In 1959 rapid rotation of the semi-stellar nucleus of M31 was discovered by [[Andre Lallemand]], M. Duschene and Merle Walker<ref>PASP 1960, p.72</ref> at the [[Lick Observatory]], using the 120-inch telescope, coudé Spectrograph, and Lallemand electronographic camera. They estimated the mass of the nucleus to be about 1.3 x 10<sup>7</sup> solar masses. The second example of this phenomenon was found in 1961 in the nucleus of M32 by M.F Walker<ref>1962 Astrophysical Journal, 136, p.692</ref> at the [[Lick Observatory]], using the same equipment as used for the discovery of the nucleus of M31. He estimated the nuclear mass to be between 0.8 and 1 x 10<sup>7</sup> solar masses. Such rotation is now considered to be evidence of the existence of supermassive black holes in the nuclei of these galaxies.
+In 1959 rapid rotation of the semi-stellar nucleus of M31 was discovered by [[Andre Lallemand]], M. Duschene and Merle Walker<ref>PASP 1960, p.72</ref> at the [[Lick Observatory]], using the 120-inch telescope, coudé Spectrograph, and Lallemand electronographic camera. They estimated the mass of the nucleus to be about 1.3 x 10<sup>7</sup> solar masses. The second example of this phenomenon was found in 1961 in the nucleus of M32 by M.F Walker<ref>1962 ''Astrophysical Journal'', 136, p.692</ref> at the [[Lick Observatory]], using the same equipment as used for the discovery of the nucleus of M31. He estimated the nuclear mass to be between 0.8 and 1 x 10<sup>7</sup> solar masses. Such rotation is now considered to be evidence of the existence of supermassive black holes in the nuclei of these galaxies.
 === 21st century ===
-[[File:Largest Mosaic of Andromeda by Hubble jan 16 2025-extra details.jpg | thumb | Largest Mosaic of Andromeda by Hubble with details: (a) Clusters of bright blue stars embedded within the galaxy, background galaxies seen much farther away, and photo-bombing by a couple bright foreground stars that are actually inside our Milky Way; (b) NGC 206 the most conspicuous star cloud in Andromeda; (c) A young cluster of blue newborn stars; (d) The satellite galaxy M32, that may be the residual core of a galaxy that once collided with Andromeda; (e) Dark dust lanes across myriad stars.<ref>{{cite web |title=Hubble's panoramic view of the Andromeda Galaxy (annotated) |url=https://esahubble.org/images/heic2501b/ |website=www.esahubble.org |access-date=17 February 2025 |language=en}}{{source-attribution}}</ref>]]
+[[File:Largest Mosaic of Andromeda by Hubble jan 16 2025-extra details.jpg| thumb|Largest Mosaic of Andromeda by Hubble with details: (a) Clusters of bright blue stars embedded within the galaxy, background galaxies seen much farther away, and photo-bombing by a couple bright foreground stars that are actually inside our Milky Way; (b) NGC 206 the most conspicuous star cloud in Andromeda; (c) A young cluster of blue newborn stars; (d) The satellite galaxy M32, that may be the residual core of a galaxy that once collided with Andromeda; (e) Dark dust lanes across myriad stars.<ref>{{cite web |title=Hubble's panoramic view of the Andromeda Galaxy (annotated) |url=https://esahubble.org/images/heic2501b/ |website=www.esahubble.org |access-date=17 February 2025 |language=en}}{{source-attribution}}</ref>]]
 In 2009, an occurrence of [[microlensing]]—a phenomenon caused by the deflection of light by a massive object—may have led to the first discovery of a planet in the Andromeda Galaxy.<ref name="Ingrosso 2009"/>
 In 2020, observations of linearly polarized radio emission with the [[Westerbork Synthesis Radio Telescope]], the [[Effelsberg 100-m Radio Telescope]], and the [[Very Large Array]] revealed ordered magnetic fields aligned along the "10-kpc ring" of gas and star formation.<ref name="Beck 2020"/>
-In 2025, NASA published a huge mosaic made by the Hubble Space Telescope, assembled from approximately 600 separate overlapping fields of view taken over 10 years of Hubble observation. Hubble resolves an estimated 200 million stars that are hotter than our Sun, but still a fraction of the galaxy’s total estimated stellar population.
+In 2023, amateur astronomers Marcel Drechsler, Xavier Strottner and Yann Sainty announced the discovery of a huge, oxygen-rich emission nebula just south of M31, near the bright star 35 And. This nebula, now classified as SDSO-1, is exceedingly faint, requiring dozens of hours of exposure time minimum to detect, and appears to only emit in [[doubly ionized oxygen|oxygen-III]].<ref>{{Cite web |title=AstroBin |url=https://app.astrobin.com/search?p=eJy7OakktaLEVtXcSdXIqCwxpzQVSKsaOwLJxLyUovzc1JREVSODxKJkkLiRM5DMTSxJzgipLECodPTxgcvm5+VUBqcC1Wd45oVkluSkFjvmpbikFicXZRaUZObnFUN0pSXmFKeqmruoFSSmp9oagqngzCog08AAAH/ALsg=&i=1d8ivk |access-date=2025-06-05 |website=app.astrobin.com}}</ref> Deep studies of the surrounding regions showed no signs of similarly bright oxygen nebulae near M31, nor any sign of connecting hydrogen filaments to SDSO-1, suggesting a high oxygen-hydrogen ratio. Current research suggests SDSO-1 is extragalactic in nature, specifically caused by interaction between the Milky Way's and M31's circumgalactic halos, although more research is needed to fully understand this object.<ref>{{cite journal |arxiv=2307.06308 |last1=Fesen |first1=Robert A. |last2=Kimeswenger |first2=Stefan |last3=Michael Shull |first3=J. |last4=Drechsler |first4=Marcel |last5=Strottner |first5=Xavier |last6=Sainty |first6=Yann |last7=Falls |first7=Bray |last8=Vergnes |first8=Christophe |last9=Martino |first9=Nicolas |last10=Walker |first10=Sean |last11=Rupert |first11=Justin |title=The Spatial and Emission Properties of the Large &#91;O III&#93; Emission Nebula Near M31 |journal=The Astrophysical Journal |date=2023 |volume=957 |issue=2 |page=82 |doi=10.3847/1538-4357/acfe0d |doi-access=free |bibcode=2023ApJ...957...82F }}</ref> A later study using spectroscopy found the nebula to be in the Milky Way.<ref name="Lumbreras-Calle2024">{{Cite arXiv |last1=Lumbreras-Calle |first1=A. |last2=Fernández-Ontiveros |first2=J. A. |last3=Infante-Sainz |first3=R. |last4=Akhlaghi |first4=M. |last5=Montoro-Molina |first5=B. |last6=Pérez-Díaz |first6=B. |last7=del Pino |first7=A. |last8=Vives-Arias |first8=H. |last9=Hernán-Caballero |first9=A. |last10=López-Sanjuan |first10=C. |last11=Martín-Guerrero |first11=M. A. |last12=Eskandarlou |first12=S. |last13=Ederoclite |first13=A. |date=December 2024 |title=Andromeda's tenuous veil: extensive nebular emission near (yet far from) M31 |class=astro-ph.GA |eprint=2412.08327}}</ref> One study found the nebula to be a [[bow shock]] of a ghost [[planetary nebula]] around the binary [[EG Andromedae]].<ref name="Ogle2025">{{Cite arXiv |last1=Ogle |first1=Patrick |last2=Petersen |first2=Mark |last3=Schaeffer |first3=Tim |last4=McCallum |first4=Lewis |last5=Noriega-Crespo |first5=Alberto |last6=Michael Rich |first6=R. |last7=Sebastian |first7=Biny |last8=Bjork |first8=Carl |last9=Body |first9=Steeve |last10=Chinnasamy |first10=Sendhil |last11=Dreschsler |first11=Marcel |last12=Kottary |first12=Tarun |last13=Sainty |first13=Yann |last14=Sparkman |first14=Patrick |last15=Strottner |first15=Xavier |title=SDSO1 is a Ghost Planetary Nebula Bow Shock in Front of M31 |date=2025 |class=astro-ph.GA |eprint=2507.15834}}</ref>
+<!-- Deleted image removed: [[File:M31arc.jpg|thumb|Discovery image of SDSO-1 by Drechsler et al, 2023]] -->
+In 2025, NASA published a huge mosaic made by the Hubble Space Telescope, assembled from approximately 600 separate overlapping fields of view taken over 10 years of Hubble observation. Hubble resolves an estimated 200 million stars that are hotter than the Sun, but still a fraction of the galaxy's total estimated stellar population.
 == General ==
@@ Line 76: / Line 80: @@
 [[File:Andromeda Galaxy 560mm FL.jpg|thumb|Processed image of the Andromeda Galaxy, with enhancement of [[H-alpha]] to highlight its star-forming regions]]
-A major [[Galaxy merger|merger]] occurred 2 to 3&nbsp;billion years ago at the Andromeda location, involving two galaxies with a mass ratio of approximately 4.<ref name="Hammer et al. 2018">{{cite journal |last1=Hammer |first1=F |last2=Yang |first2=Y B |last3=Wang |first3=J L |last4=Ibata |first4=R |last5=Flores |first5=H |last6=Puech |first6=M |title=A 2–3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts |journal=Monthly Notices of the Royal Astronomical Society |date=1 April 2018 |volume=475 |issue=2 |pages=2754–2767 |doi=10.1093/mnras/stx3343|doi-access=free |arxiv=1801.04279 }}</ref><ref name="D'Souza and Bell">{{cite journal |last1=D’Souza |first1=Richard |last2=Bell |first2=Eric F. |title=The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor |journal=Nature Astronomy |date=September 2018 |volume=2 |issue=9 |pages=737–743 |doi=10.1038/s41550-018-0533-x |arxiv=1807.08819 |bibcode=2018NatAs...2..737D |s2cid=256713163 |url=https://www.nature.com/articles/s41550-018-0533-x |language=en |issn=2397-3366}}</ref>
+A major [[Galaxy merger|merger]] occurred 2 to 3&nbsp;billion years ago at the Andromeda location, involving two galaxies with a mass ratio of approximately 4.<ref name="Hammer et al. 2018">{{cite journal |last1=Hammer |first1=F |last2=Yang |first2=Y B |last3=Wang |first3=J L |last4=Ibata |first4=R |last5=Flores |first5=H |last6=Puech |first6=M |title=A 2–3 billion year old major merger paradigm for the Andromeda galaxy and its outskirts |journal=Monthly Notices of the Royal Astronomical Society |date=1 April 2018 |volume=475 |issue=2 |pages=2754–2767 |doi=10.1093/mnras/stx3343|doi-access=free |arxiv=1801.04279 }}</ref><ref name="D'Souza and Bell">{{cite journal |last1=D'Souza |first1=Richard |last2=Bell |first2=Eric F. |title=The Andromeda galaxy's most important merger about 2 billion years ago as M32's likely progenitor |journal=Nature Astronomy |date=September 2018 |volume=2 |issue=9 |pages=737–743 |doi=10.1038/s41550-018-0533-x |arxiv=1807.08819 |bibcode=2018NatAs...2..737D |s2cid=256713163 |url=https://www.nature.com/articles/s41550-018-0533-x |language=en |issn=2397-3366}}</ref>
 The discovery of a recent merger in the Andromeda galaxy was first based on interpreting its anomalous age-velocity dispersion relation,<ref name="Dorman et al. 2014">{{Cite journal |last1=Dorman |first1=Claire E. |last2=Guhathakurta |first2=Puragra |last3=Seth |first3=Anil C. |last4=Weisz |first4=Daniel R. |last5=Bell |first5=Eric F. |last6=Dalcanton |first6=Julianne J. |last7=Gilbert |first7=Karoline M. |last8=Hamren |first8=Katherine M. |last9=Lewis |first9=Alexia R. |last10=Skillman |first10=Evan D. |last11=Toloba |first11=Elisa |last12=Williams |first12=Benjamin F. |date=9 April 2015 |title=A clear age-velocity dispersion correlation in Andromeda's stellar disk |journal=The Astrophysical Journal |volume=803 |issue=1 |pages=24 |arxiv=1502.03820 |bibcode=2015ApJ...803...24D |doi=10.1088/0004-637X/803/1/24 |s2cid=119223754}}</ref> as well as the fact that 2&nbsp;billion years ago, star formation throughout Andromeda's disk was much more active than today.<ref name="Williams et al. 2015">{{Cite journal |last1=Williams |first1=Benjamin F. |last2=Dalcanton |first2=Julianne J. |last3=Dolphin |first3=Andrew E. |last4=Weisz |first4=Daniel R. |last5=Lewis |first5=Alexia R. |last6=Lang |first6=Dustin |last7=Bell |first7=Eric F. |last8=Boyer |first8=Martha |last9=Fouesneau |first9=Morgan |last10=Gilbert |first10=Karoline M. |last11=Monachesi |first11=Antonela |last12=Skillman |first12=Evan |date=5 June 2015 |title=A Global Star-forming Episode in M31 2-4 Gyr Ago |journal=The Astrophysical Journal |volume=806 |issue=1 |pages=48 |arxiv=1504.02120 |bibcode=2015ApJ...806...48W |doi=10.1088/0004-637X/806/1/48 |s2cid=118435748}}</ref>
@@ Line 82: / Line 86: @@
 Modeling<ref name="Hammer et al. 2018"/> of this violent collision shows that it has formed most of the galaxy's (metal-rich) [[galactic halo]], including the Giant Stream,<ref name="Ibata et al. 2001">{{cite journal |last1=Ibata |first1=Rodrigo |last2=Irwin |first2=Michael |last3=Lewis |first3=Geraint |last4=Ferguson |first4=Annette M. N. |last5=Tanvir |first5=Nial |title=A giant stream of metal-rich stars in the halo of the galaxy M31 |journal=Nature |date=July 2001 |volume=412 |issue=6842 |pages=49–52 |doi=10.1038/35083506|pmid=11452300 |arxiv=astro-ph/0107090 |bibcode=2001Natur.412...49I |s2cid=4413139 }}</ref> and also the extended thick disk, the young age thin disk, and the static 10 kpc ring. During this epoch, its rate of [[star formation]] would have been [[Starburst galaxy|very high]], to the point of becoming a [[luminous infrared galaxy]] for roughly 100 million years. Modeling also recovers the bulge profile, the large bar, and the overall halo density profile.
-Andromeda and the [[Triangulum Galaxy]] (M33) might have had a very close passage 2–4&nbsp;billion years ago, but it seems unlikely from the last measurements from the Hubble Space Telescope.<ref name="Patel et al. 2017">{{cite journal |last1=Patel |first1=Ekta |last2=Besla |first2=Gurtina |last3=Sohn |first3=Sangmo Tony |title=Orbits of massive satellite galaxies – I. A close look at the Large Magellanic Cloud and a new orbital history for M33 |journal=Monthly Notices of the Royal Astronomical Society |date=1 February 2017 |volume=464 |issue=4 |pages=3825–3849 |doi=10.1093/mnras/stw2616|doi-access=free |hdl=10150/623269 |hdl-access=free }}</ref>
+Andromeda and the [[Triangulum Galaxy]] (M33) might have had a very close passage 2–4&nbsp;billion years ago, but it seems unlikely from the last measurements from the Hubble Space Telescope.<ref name="Patel et al. 2017">{{cite journal |last1=Patel |first1=Ekta |last2=Besla |first2=Gurtina |last3=Sohn |first3=Sangmo Tony |title=Orbits of massive satellite galaxies – I. A close look at the Large Magellanic Cloud and a new orbital history for M33 |journal=Monthly Notices of the Royal Astronomical Society |date=1 February 2017 |volume=464 |issue=4 |pages=3825–3849 |doi=10.1093/mnras/stw2616|doi-access=free |hdl=10150/623269 |hdl-access=free |arxiv=1609.04823 }}</ref>
 === Distance estimate ===
@@ Line 119: / Line 123: @@
 A study in 2005 by the [[Keck telescopes]] shows the existence of a tenuous sprinkle of stars, or [[galactic halo]], extending outward from the galaxy.<ref name="Chapman et al 2006"/> The stars in this halo behave differently from the ones in Andromeda's main galactic disc, where they show rather disorganized orbital motions as opposed to the stars in the main disc having more orderly orbits and uniform velocities of 200&nbsp;km/s.<ref name="Chapman et al 2006"/> This diffuse halo extends outwards away from Andromeda's main disc with the diameter of {{convert|67.45|kpc|ly|sigfig=3|abbr=off}}.<ref name="Chapman et al 2006"/>
-The galaxy is inclined an estimated 77° relative to Earth (where an angle of 90° would be edge-on). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk.<ref name="UC Santa Cruz 2001"/> A possible cause of such a warp could be gravitational interaction with the satellite galaxies near the Andromeda Galaxy. The Galaxy [[Triangulum Galaxy|M33]] could be responsible for some warp in Andromeda's arms, though more precise distances and radial velocities are required.
+The galaxy is inclined an estimated 77° relative to Earth (where an angle of 90° would be edge-on). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk.<ref name="UC Santa Cruz 2001"/> A possible cause of such a warp could be gravitational interaction with the satellite galaxies near the Andromeda Galaxy. The Galaxy [[Triangulum Galaxy|M33]] could be responsible for some warp in Andromeda's arms, though more precise distances and radial velocities are required.{{original research inline|date=August 2025}}
 Spectroscopic studies have provided detailed measurements of the [[Galaxy rotation curve|rotational velocity of the Andromeda Galaxy]] as a function of radial distance from the core. The rotational velocity has a maximum value of {{cvt|225|km/s}} at {{convert|1300|ly|e6AU|lk=on|abbr=unit}} from the core, and it has its minimum possibly as low as {{cvt|50|km/s}} at {{convert|7000|ly|e6AU|abbr=unit}} from the core. Further out, rotational velocity rises out to a radius of {{convert|33000|ly|e9AU|abbr=unit}}, where it reaches a peak of {{cvt|250|km/s}}. The velocities slowly decline beyond that distance, dropping to around {{cvt|200|km/s}} at {{convert|80000|ly|e9AU|abbr=unit}}. These velocity measurements imply a concentrated mass of about {{Solar mass|6{{e|9}}|link=y}} in the [[Galaxy nucleus|nucleus]]. The total mass of the galaxy increases [[linearity|linearly]] out to {{convert|45000|ly|e9AU|abbr=unit}}, then more slowly beyond that radius.<ref name="Rubin & Ford 1970"/>
@@ Line 187: / Line 191: @@
 === PA-99-N2 event and possible exoplanet in galaxy ===
 {{Main|PA-99-N2}}
 PA-99-N2 was a microlensing event detected in the Andromeda Galaxy in 1999. One of the explanations for this is the gravitational lensing of a red giant by a star with a mass between 0.02 and 3.6 times that of the [[Sun]], which suggested that the star is likely orbited by a planet. This possible exoplanet would have a mass 6.34 times that of Jupiter. If finally confirmed, it would be the first ever found [[extragalactic planet]]. However, anomalies in the event were later found.<ref name="Better needed"/>
 == Nearby and satellite galaxies ==
 {{Main|Andromeda's satellite galaxies}}
 [[File:M31, the Andromeda Galaxy, Killarney Provincial Park Observatory.jpg|thumb|The Andromeda Galaxy with [[Satellite galaxy|satellite galaxies]] [[Messier 32|M32]] (center left above the [[galactic nucleus]]) and [[Messier 110|M110]] (center right below the galaxy)]]
 Like the Milky Way, the Andromeda Galaxy has smaller [[satellite galaxy|satellite galaxies]], consisting of over 20 known [[dwarf galaxy|dwarf galaxies]]. The Andromeda Galaxy's dwarf galaxy population is very similar to the Milky Way's, but the galaxies are much more numerous.<ref>{{cite journal|doi=10.1093/mnras/stab1754|title=Solo dwarfs IV: Comparing and contrasting satellite and isolated dwarf galaxies in the Local Group|year=2021|last1=Higgs|first1=C. R.|last2=McConnachie|first2=A. W.|journal=Monthly Notices of the Royal Astronomical Society|volume=506|issue=2|pages=2766–2779|doi-access=free |arxiv=2106.12649}}</ref> The best-known and most readily observed satellite galaxies are [[Elliptical Galaxy M32|M32]] and [[Elliptical Galaxy M110|M110]]. Based on current evidence, it appears that M32 underwent a close encounter with the Andromeda Galaxy in the past. M32 may once have been a larger galaxy that had its stellar disk removed by M31 and underwent a sharp increase of [[star formation]] in the core region, which lasted until the relatively recent past.<ref name="Bekki et al 2001"/>
@@ Line 202: / Line 208: @@
 == Collision with the Milky Way ==
 {{Main|Andromeda–Milky Way collision}}
 [[File:Collision paths of our Milky Way galaxy and the Andromeda galaxy.jpg|thumb|300x300px|Illustration of the collision path between the Milky Way and Andromeda Galaxy]]
-The Andromeda Galaxy is approaching the Milky Way at about {{convert|110|km|abbr=off}} per second.<ref name="nature"/> It has been measured approaching relative to the Sun at around {{cvt|300|km/s}}<ref name="ned"/> as the Sun orbits around the center of the galaxy at a speed of approximately {{cvt|225|km/s}}. This makes the Andromeda Galaxy one of about 100 observable [[blueshift]]ed galaxies.<ref name="Answers"/> Andromeda Galaxy's tangential or sideways velocity concerning the Milky Way is relatively much smaller than the approaching velocity and therefore it is expected to collide directly with the Milky Way in about 2.5–4&nbsp;billion years. A likely outcome of the collision is that the [[Galaxy merger|galaxies will merge]] to form a giant [[elliptical galaxy]]<ref name="Cox & Loeb 2008"/> or possibly large [[disc galaxy]].<ref name="Ueda2014"/> Such events are frequent among the galaxies in [[galaxy group]]s. The fate of Earth and the [[Solar System]] in the event of a collision is currently unknown. Before the galaxies merge, there is a small chance that the Solar System could be ejected from the Milky Way or join the Andromeda Galaxy.<ref name="Cain 2007"/>
+The Andromeda Galaxy is approaching the Milky Way at about {{convert|110|km|abbr=off}} per second.<ref name="nature"/> It has been measured approaching relative to the Sun at around {{cvt|300|km/s}}<ref name="ned"/> as the Sun orbits around the center of the galaxy at a speed of approximately {{cvt|225|km/s}}. This makes the Andromeda Galaxy one of about 100 observable [[blueshift]]ed galaxies.<ref name="Answers"/> Andromeda Galaxy's tangential or sideways velocity concerning the Milky Way is uncertain, but estimated to be smaller than the approaching velocity. After the sideways velocity was first measured, Andromeda was predicted to collide directly with the Milky Way in about 4&nbsp;billion years.<ref name="Sohn">{{Cite journal |last1=Sohn |first1=Sangmo Tony |last2=Anderson |first2=Jay |last3=van der Marel |first3=Roeland P. |name-list-style=and |date=2012-07-01 |title=The M31 velocity vector. I. The Hubble Space Telescope proper-motion measurements |journal=[[The Astrophysical Journal]] |volume=753 |issue=1 |pages=7 |arxiv=1205.6863 |bibcode=2012ApJ...753....7S |doi=10.1088/0004-637X/753/1/7 |issn=0004-637X |s2cid=53071357}}</ref> However, later calculations, including a higher sideways velocity measurement from the [[Gaia (spacecraft)]] and the effect of other [[Local Group]] galaxies found a much lower probability of a merger.<ref name=":2">{{Cite journal|title=No certainty of a Milky Way–Andromeda collision|first1=Till|last1=Sawala|first2=Jehanne|last2=Delhomelle|first3=Alis J.|last3=Deason|first4=Carlos S.|last4=Frenk|first5=Jenni|last5=Häkkinen|first6=Peter H.|last6=Johansson|first7=Atte|last7=Keitaanranta|first8=Alexander|last8=Rawlings|first9=Ruby|last9=Wright|display-authors=3|journal=[[Nature Astronomy]]|date=2 June 2025|volume=9 |issue=8 |pages=1206–1217 |doi=10.1038/s41550-025-02563-1|doi-access=free|arxiv=2408.00064 |bibcode=2025NatAs...9.1206S }}</ref>
+A likely outcome of the collision would be that the [[Galaxy merger|galaxies will merge]] to form a giant [[elliptical galaxy]]<ref name="Cox & Loeb 2008"/> or possibly large [[disc galaxy]].<ref name="Ueda2014"/> Such events are frequent among the galaxies in [[galaxy group]]s. The fate of Earth and the [[Solar System]] in the event of a collision is currently unknown. Before the galaxies merge, there is a small chance that the Solar System could be ejected from the Milky Way or join the Andromeda Galaxy.<ref name="Cain 2007"/>
-== Amateur observation==
+==Amateur observation==
 [[File:Moon over Andromeda (rotated).jpg|thumb|Superimposing picture showing sizes of the Moon and the Andromeda Galaxy as observed from Earth. Note that this photographic image shows much more of the galaxy's darker outer regions than an amateur observer is able to see.<ref>{{cite web |last1=Plait |first1=Phil |title=Yes, That Picture of the Moon and the Andromeda Galaxy Is About Right |url=https://slate.com/technology/2014/01/moon-and-andromeda-relative-size-in-the-sky.html |website=Slate Magazine |access-date=29 July 2022 |language=en |date=1 January 2014}}</ref><ref>{{cite web |title=Andromeda and the Moon collage |url=https://noirlab.edu/public/images/noao-andromn/ |website=www.noirlab.edu |access-date=29 July 2022 |language=en}}</ref>]]
@@ Line 212: / Line 221: @@
 Andromeda is best seen during autumn nights in the [[Northern Hemisphere]] when it passes high overhead, reaching its [[zenith|highest point]] around midnight in October, and two hours earlier each successive month. In the early evening, it rises in the east in September and sets in the west in February.<ref name=physics/>
 From the [[Southern Hemisphere]] the Andromeda Galaxy is visible between October and December, best viewed from as far north as possible. [[Binoculars]] can reveal some larger structures of the galaxy and its two brightest [[Satellite galaxy|satellite galaxies]], [[Messier 32|M32]] and [[Messier 110|M110]].<ref name="S&T"/> An [[Amateur astronomy|amateur telescope]] can reveal Andromeda's disk, some of its brightest globular clusters, dark dust lanes, and the large star cloud [[NGC 206]].<ref name=Backyard/><ref name="A-Mall"/>
+== Gallery ==
+<gallery>
+File: M31-Andromede-16-09-2023-Hamois.jpg|A visible light image of the Andromeda Galaxy and two satellite galaxies. [[Messier 32]] is above the galactic nucleus and [[Messier 110]] is at the bottom.
+</gallery>
 ==See also==
@@ Line 245: / Line 259: @@
 == References ==
-{{reflist|refs=
+<references>
 <ref name="ned">{{cite web | title = Results for Messier 31 | url = http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=M+031&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES | work = NASA/IPAC Extragalactic Database | publisher = [[NASA]]/[[Infrared Processing and Analysis Center|IPAC]] | access-date = 28 February 2019}}</ref>
 <ref name="nature">{{cite journal | last1 = Cowen | first1 = Ron | date = 2012 | title = Andromeda on collision course with the Milky Way | journal = [[Nature (journal)|Nature]] | doi = 10.1038/nature.2012.10765 | s2cid = 124815138}}</ref>
@@ Line 296: / Line 311: @@
 <ref name="Peterson 1973">{{Cite book |last=Peterson |first=L. E. |title=X- and Gamma-Ray Astronomy |chapter-url=http://link.springer.com/10.1007/978-94-010-2585-0_5 |chapter=Hard Cosmic X-ray Sources |date=1973 |publisher=Springer Netherlands |isbn=978-90-277-0337-8 |editor-last=Bradt |editor-first=H. |location=Dordrecht |pages=51–73 |language=en |doi=10.1007/978-94-010-2585-0_5 |editor-last2=Giacconi |editor-first2=R.}}</ref>
 <ref name="Marelli et al. 2017">{{cite journal | last1=Marelli | first1=Martino | last2=Tiengo | first2=Andrea | last3=De Luca | first3=Andrea | display-authors=3 | last4=Salvetti | first4=David | last5=Saronni | first5=Luca | last6=Sidoli | first6=Lara | last7=Paizis | first7=Adamantia | last8=Salvaterra | first8=Ruben | last9=Belfiore | first9=Andrea | last10=Israel | first10=Gianluca | last11=Haberl | first11=Frank | last12=D'Agostino | first12=Daniele | date=2017 | title=Discovery of periodic dips in the brightest hard X-ray source of M31 with EXTraS | journal=The Astrophysical Journal Letters | volume=851 | issue=2 | pages=L27 | bibcode=2017ApJ...851L..27M | doi=10.3847/2041-8213/aa9b2e | arxiv=1711.05540 | s2cid=119266242 | doi-access=free }}</ref>
-<ref name="Barnard Kolb & Osborne 2005">{{cite arXiv | last1 = Barnard | first1 = Robin | last2 = Kolb | first2 = Ulrich C. | last3 = Osborne | first3 = Julian P. | date = 2005 | title = Timing the bright X-ray population of the core of M31 with XMM-Newton | eprint = astro-ph/0508284}}</ref>
+<ref name="Barnard Kolb & Osborne 2005">{{cite arXiv | last1 = Barnard | first1 = Robin | last2 = Kolb | first2 = Ulrich C. | last3 = Osborne | first3 = Julian P. | date = 2005 | title = Timing the bright X-ray population of the core of M31 with XMM-Newton | eprint = astro-ph/0508284 }}</ref>
 <ref name="Barmby & Huchra 2001">{{cite journal | last1=Barmby |first1=Pauline | last2=Huchra |first2=John P. | date = 2001 | title = M31 Globular Clusters in the ''Hubble Space Telescope'' Archive. I. Cluster Detection and Completeness | journal = [[Astronomical Journal]] | volume = 122 | issue = 5 | pages = 2458–2468 | doi = 10.1086/323457 | bibcode = 2001AJ....122.2458B | arxiv = astro-ph/0107401 | s2cid=117895577}}</ref>
 <ref name="hubblesite 1996-04-24">{{cite press release | publisher = Hubble news desk STSci-1996-11 | date = 24 April 1996 | title = Hubble Spies Globular Cluster in Neighboring Galaxy | url = http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/11/ | access-date = 26 May 2006 | archive-url = https://web.archive.org/web/20060701083419/http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/11/ | archive-date = 1 July 2006 | url-status = live}}</ref>
@@ Line 307: / Line 322: @@
 <ref name="Cox & Loeb 2008">{{cite journal | last1 = Cox | first1 = T. J. | last2 = Loeb | first2 = Abraham |author-link2=Abraham Loeb| date = 2008 | title = The collision between the Milky Way and Andromeda | journal = [[Monthly Notices of the Royal Astronomical Society]] | volume = 386 | issue = 1 | pages = 461–474 | bibcode = 2008MNRAS.386..461C | doi = 10.1111/j.1365-2966.2008.13048.x | doi-access = free | arxiv = 0705.1170 | s2cid = 14964036}}</ref>
 <ref name="Cain 2007">{{cite web | last = Cain | first = Fraser | date = 2007 | title = When Our Galaxy Smashes Into Andromeda, What Happens to the Sun? | work = [[Universe Today]] | url = http://www.universetoday.com/2007/05/10/when-our-galaxy-smashes-into-andromeda-what-happens-to-the-sun/ | access-date = 16 May 2007 | archive-url = https://web.archive.org/web/20070517021426/http://www.universetoday.com/2007/05/10/when-our-galaxy-smashes-into-andromeda-what-happens-to-the-sun/ | archive-date = 17 May 2007 | url-status = live}}</ref>
-<ref name="Moskvitch 2010">{{cite news | last = Moskvitch | first = Katia | date = 25 November 2010 | title = Andromeda 'born in a collision' | url = http://www.bbc.co.uk/news/science-environment-11833356 | work = [[BBC News]] | access-date = 25 November 2010 | archive-url = https://web.archive.org/web/20101126042510/http://www.bbc.co.uk/news/science-environment-11833356 | archive-date = 26 November 2010 | url-status = live}}</ref>
+<ref name="Moskvitch 2010">{{cite news | last = Moskvitch | first = Katia | date = 25 November 2010 | title = Andromeda 'born in a collision' | url = https://www.bbc.co.uk/news/science-environment-11833356 | work = [[BBC News]] | access-date = 25 November 2010 | archive-url = https://web.archive.org/web/20101126042510/http://www.bbc.co.uk/news/science-environment-11833356 | archive-date = 26 November 2010 | url-status = live}}</ref>
 <ref name="adam">{{cite journal|arxiv=1110.3769|doi=10.1088/0004-637X/745/2/156|title=Cepheid Period-Luminosity Relations in the Near-Infrared and the Distance to M31 from Thehubble Space Telescopewide Field Camera 3|year=2012|last1=Riess|first1=Adam G.|last2=Fliri|first2=Jürgen|last3=Valls-Gabaud|first3=David|journal=The Astrophysical Journal|volume=745|issue=2|page=156|bibcode=2012ApJ...745..156R|s2cid=119113794}}</ref>
 <ref name="Kafle2018">{{cite journal | first1 = Prajwal R. |last1=Kafle | first2 = Sanjib |last2=Sharma | first3 = Geraint F. |last3=Lewis | display-authors=3 | first4 = Aaron S. G. |last4=Robotham | first5 = Simon P. | last5=Driver | title = The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda Galaxy | journal = Monthly Notices of the Royal Astronomical Society | volume = 475 | issue = 3 | date = 1 February 2018 | pages=4043–4054 | bibcode = 2018MNRAS.475.4043K | issn=0035-8711 | doi = 10.1093/mnras/sty082|doi-access=free |arxiv = 1801.03949 |s2cid=54039546}}</ref>
@@ Line 340: / Line 355: @@
 <ref name="GalaxyMass">"The median values of the Milky Way and Andromeda masses are M<sub>G</sub> = {{val|0.8|0.4|0.3|e=12|u=solar mass}} and M<sub>A</sub> = {{val|1.5|0.5|0.4|e=12|u=solar mass}} at a 68% level" {{cite journal | first1=Jorge |last1=Peñarrubia | first2=Yin-Zhe |last2=Ma | first3=Matthew G. |last3=Walker | first4=Alan W. |last4=McConnachie | title=A dynamical model of the local cosmic expansion | journal=Monthly Notices of the Royal Astronomical Society | volume=433 | issue=3 | date=29 July 2014 | pages=2204–2222 | bibcode= 2014MNRAS.443.2204P | doi=10.1093/mnras/stu879|doi-access=free |arxiv = 1405.0306 |s2cid=119295582}}, but compare "[we estimate] the virial mass and radius of the galaxy to be {{cvt|0.8|+/-|0.1|e12solar mass|kg|lk=on}}" {{cite journal | first1 = Prajwal R. |last1=Kafle | first2 = Sanjib |last2=Sharma | first3 = Geraint F. |last3=Lewis | display-authors=3 | first4 = Aaron S. G. |last4=Robotham | first5 = Simon P. | last5=Driver | title = The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda Galaxy | journal = Monthly Notices of the Royal Astronomical Society | volume = 475 | issue = 3 | date = 1 February 2018 | pages=4043–4054 | bibcode = 2018MNRAS.475.4043K | issn=0035-8711 | doi = 10.1093/mnras/sty082|doi-access=free |arxiv = 1801.03949 |s2cid=54039546}}</ref>
 <ref name="As-Now">{{Cite web |date=11 March 2019 |title=Milky Way tips the scales at 1.5 trillion solar masses |url=https://astronomynow.com/2019/03/11/milky-way-tips-the-scales-at-1-5-trillion-solar-masses/ |access-date=2024-09-11 |website=Astronomy Now |language=en-US}}</ref>
-<ref name="Schiavi">{{cite journal|last1=Schiavi|first1=Riccardo|last2=Capuzzo-Dolcetta|first2=Roberto|last3=Arca-Sedda|first3=Manuel|last4=Spera|first4=Mario|title=Future merger of the Milky Way with the Andromeda galaxy and the fate of their supermassive black holes|journal=Astronomy & Astrophysics|date=October 2020|volume=642|pages=A30|doi=10.1051/0004-6361/202038674|bibcode=2020A&A...642A..30S|arxiv=2102.10938|s2cid=224991193}}</ref>
-<ref name="Messie">{{cite web |url=https://messierobjects101.com/messier-object-m31-m32-m110-andromeda-galaxy/ |title=M 31, M 32 & M 110 |date=15 October 2016}}</ref>
+<ref name="Messie">{{cite web |url=https://messierobjects101.com/messier-object-m31-m32-m110-andromeda-galaxy/ |title=M 31, M 32 & M 110 |work=Messier Objects Mobile -- Charts, Maps & Photos |date=15 October 2016}}</ref>
 <ref name="Hafez">{{Cite thesis | last= Hafez | first= Ihsan | date= 2010 | title= Abd al-Rahman al-Sufi and his book of the fixed stars: a journey of re-discovery. | url= http://eprints.jcu.edu.au/28854/ | type= PhD Thesis | publisher= James Cook University | access-date= 23 June 2016 | bibcode= 2010PhDT.......295H}}</ref>
 <ref name="Kant">{{Cite book |last=Kant |first=Immanuel |author-link=Immanuel Kant |url=https://archive.org/details/universalnatural0000kant |title=Universal natural history and theory of the heavens |date=1969 |publisher=University of Michigan Press}}</ref>
@@ Line 359: / Line 374: @@
 <ref name="Massive">{{Cite web |title = Hubble finds massive halo around the Andromeda Galaxy |url = https://news.nd.edu/news/hubble-finds-halo-around-the-andromeda-galaxy/ |website = University of Notre Dame News |date = 7 May 2015 |first=Marissa |last=Gebhard}}</ref>
 <ref name="Evidence">{{Cite journal |title = Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy |journal = The Astrophysical Journal |arxiv = 1404.6540 |date = 25 April 2014 |first1 = Nicolas |last1 = Lehner |first2 = Chris |last2 = Howk |first3 = Bart |last3 = Wakker |doi=10.1088/0004-637x/804/2/79 |bibcode=2015ApJ...804...79L |volume=804 |issue = 2 |pages=79 |s2cid = 31505650}}</ref>
-<ref name="HaloFind">{{Cite web|title = NASA's Hubble Finds Giant Halo Around the Andromeda Galaxy |url = http://www.nasa.gov/feature/goddard/nasa-s-hubble-finds-giant-halo-around-the-andromeda-galaxy|access-date = 7 May 2015|date = 7 May 2015}}</ref>
+<ref name="HaloFind">{{Cite web| last1=Jenner | first1=Lynn |title = NASA's Hubble Finds Giant Halo Around the Andromeda Galaxy | work=NASA |url = http://www.nasa.gov/feature/goddard/nasa-s-hubble-finds-giant-halo-around-the-andromeda-galaxy|access-date = 7 May 2015|date = 7 May 2015}}</ref>
 <ref name="MWAY">{{cite journal |doi=10.1088/0004-637X/736/2/84 |title=The Mid-life Crisis of the Milky Way and M31 |date=2011 |last1=Mutch |first1=Simon J. |last2=Croton | first2=Darren J. |last3=Poole | first3=Gregory B. |journal=The Astrophysical Journal |volume=736 |issue=2 |bibcode = 2011ApJ...736...84M |arxiv = 1105.2564 |pages=84 |s2cid=119280671}}</ref>
 <ref name="And-Scand">{{cite web|title=Andromeda Galaxy Scanned with High-Energy X-ray Vision|website = [[Jet Propulsion Laboratory]]|url=https://www.jpl.nasa.gov/news/news.php?feature=4811 |date=5 January 2016 |access-date=22 September 2018}}</ref>
@@ Line 371: / Line 386: @@
 <ref name="Backyard">{{cite web|url=http://www.backyard-astro.com/focusonarchive/m31/m31.html#Anchor-11481|title=Observing M31, the Andromeda Galaxy|access-date=5 October 2016|archive-date=5 August 2020|archive-url=https://web.archive.org/web/20200805132930/http://backyard-astro.com/focusonarchive/m31/m31.html#Anchor-11481|url-status=dead}}</ref>
 <ref name="A-Mall">{{Cite web|url=https://www.astronomy-mall.com/Adventures.In.Deep.Space/gcm31.htm|title=Globular Clusters in the Andromeda Galaxy|website=www.astronomy-mall.com}}</ref>
-}}
+</references>
 == External links ==
@@ Line 391: / Line 407: @@
 * [http://www.solstation.com/x-objects/andromeda.htm Andromeda Galaxy] at SolStation.com
 * [https://www.daviddarling.info/encyclopedia/A/Andromeda.html Andromeda Galaxy at The Encyclopedia of Astrobiology, Astronomy, & Spaceflight]
-* [http://www.nightskyinfo.com/archive/m31_galaxy M31, the Andromeda Galaxy] at NightSkyInfo.com
+* [http://www.nightskyinfo.com/archive/m31_galaxy M31, the Andromeda Galaxy] {{Webarchive|url=https://web.archive.org/web/20101229012601/http://www.nightskyinfo.com/archive/m31_galaxy |date=29 December 2010 }} at NightSkyInfo.com
 * {{cite news |last=Than |first=Ker |title=Strange Setup: Andromeda's Satellite Galaxies All Lined Up |url=http://space.com/scienceastronomy/060123_andromeda_plane.html |work=Space.com |date=23 January 2006}}
 * [https://web.archive.org/web/20110719204305/http://cbat.eps.harvard.edu/CBAT_M31.html M31 (Apparent) Novae Page] (IAU)
@@ Line 399: / Line 415: @@
 * [https://hubblesite.org/contents/news-releases/2015/news-2015-02.html Hubble's High-Definition Panoramic View of the Andromeda Galaxy]
 * [https://hubblesite.org/contents/media/images/2022/027/01G4NM6207PRA9YES60C5RKKA5 Infrared-Radio Image of the Andromeda Galaxy (M31)]
-* [https://rockchucksummit.com/m31-andromeda-galaxy/ Creative Commons Astrophotography M31 Andromeda image download & processing guide]
+* [https://rockchucksummit.com/m31-andromeda-galaxy/ Creative Commons Astrophotography M31 Andromeda image download & processing guide] {{Webarchive|url=https://web.archive.org/web/20210124154424/https://rockchucksummit.com/m31-andromeda-galaxy/ |date=24 January 2021 }}
+* {{cite news |last1=Achenbach |first1=Joel |first2=Shikha |last2=Subramaniam | first3= Aadit |last3= Tambe |title=Hubble telescope zooms in on the galaxy next door. |url=https://www.washingtonpost.com/science/interactive/2025/hubble-telescope-andromeda-galaxy-explore/ |access-date=17 July 2025 |newspaper=[[Washington Post]] |publisher=[[Nash Holdings]] |date=17 July 2025}} "Guided Tour" interactive website.
 {{Andromeda galaxy}}

Andromeda Galaxy: Difference between revisions

Latest revision as of 15:13, 18 November 2025

Contents

Observation history

"Island universes" hypothesis

21st century

General

Formation and history

Distance estimate

Mass estimates

Luminosity estimates

Structure

Nucleus

Discrete sources

Globular clusters

PA-99-N2 event and possible exoplanet in galaxy

Nearby and satellite galaxies

Collision with the Milky Way

Amateur observation

Gallery

See also

Notes

References

External links

Navigation menu

Andromeda Galaxy: Difference between revisions

Latest revision as of 15:13, 18 November 2025

Observation history

"Island universes" hypothesis

21st century

General

Formation and history

Distance estimate

Mass estimates

Luminosity estimates

Structure

Nucleus

Discrete sources

Globular clusters

PA-99-N2 event and possible exoplanet in galaxy

Nearby and satellite galaxies

Collision with the Milky Way

Amateur observation

Gallery

See also

Notes

References

External links

Navigation menu

Search