Local Group: Difference between revisions

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| name                = Local Group
| name                = Local Group
| image              = Local Group and nearest galaxies.jpg
| image              = Local Group and nearest galaxies.jpg
| image_scale        = 1.5
| image_scale        = 1.2
| alt                = Local Group of galaxies, including the massive members [[Messier 31]] (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
| alt                = Local Group of galaxies, including the massive members [[Messier 31]] (Andromeda Galaxy) and Milky Way, as well as other [[List of nearest galaxies|nearby galaxies]]. The center of the group is located between the two major galaxies.
| caption            = Local Group of galaxies, including the massive members [[Messier 31]] (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
| caption            = Local Group of galaxies, including the massive members [[Messier 31]] (Andromeda Galaxy) and Milky Way, as well as other [[List of nearest galaxies|nearby galaxies]]. The center of the group is located between the two major galaxies.
| epoch              = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| epoch              = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| constellation      =  
| constellation      = [[Andromeda (constellation)|Andromeda]] (''barycenter'')<ref name=makarov/>
| ra                  =  
| ra                  =  
| dec                =  
| dec                =  
| brightest_member    =  
| brightest_member    = [[Andromeda Galaxy]]<ref name=icc>{{cite web|title=Galaxy population |url=https://icc.dur.ac.uk/~tt/Lectures/Galaxies/TeX/lec/node53.html}}</ref>
| member_no          =  
| member_no          = 134+<ref name=makarov>{{cite journal|last1=Makarov |first1=Danila |last2=Makarov |first2=Dmitry |last3=Makarova |first3=Lidia |last4=Libeskind |first4=Noam |title=The frozen outskirts: A cold Hubble flow and the mass of the Local Group |journal=Astronomy & Astrophysics |date=2025 |volume=698 |pages=A178 |doi=10.1051/0004-6361/202554778 |arxiv=2505.06642 |bibcode=2025A&A...698A.178M }}</ref>
| parent              = [[Virgo Supercluster]]
| parent              = [[Local Sheet]]<ref name="marshall2014"/>
| major_axis_mpc      =  
| major_axis_mpc      = {{cvt|5.11|Mpc|Mly|sigfig=3|abbr=on|lk=on|order=flip}}<ref name="marshall2014"/>
| minor_axis_mpc      =  
| minor_axis_mpc      = {{cvt|101|kpc|ly|sigfig=3|abbr=on|lk=on|order=flip}}<ref name="banik">{{cite journal|last1=Banik |first1=Indranil |last2=Zhao |first2=Hongsheng |title=A plane of high-velocity galaxies across the Local Group |journal=Monthly Notices of the Royal Astronomical Society |date=2018 |volume=473 |issue=3 |pages=4033–4054 |doi=10.1093/mnras/stx2596 |doi-access=free |arxiv=1701.06559 }}</ref>
| richness            =  
| richness            =  
| bmtype              =  
| bmtype              =  
| velocity_dispersion =  
| velocity_dispersion = {{val|49|ul=km/s}}<ref name=elahi>{{cite journal|last1=Elahi |first1=Pascal J. |last2=Power |first2=Chris |last3=Lagos |first3=Claudia del P. |last4=Poulton |first4=Rhys |last5=Robotham |first5=Aaron S G. |title=Using velocity dispersion to estimate halo mass: Is the Local Group in tension with ΛCDM? |journal=Monthly Notices of the Royal Astronomical Society |date=2018 |volume=477 |pages=616–623 |doi=10.1093/mnras/sty590 |doi-access=free |arxiv=1712.01989 }}</ref>
| redshift            =  
| redshift            =  
| distance            =  
| distance            = {{cvt|447|+/-|26|kpc|ly|sigfig=4|abbr=on|lk=on|order=flip}} (''barycenter'')<ref name=makarov/>
| temperature        =  
| temperature        = {{val|2|-|3|e=6|ul=K}}<ref name=maloney>{{cite journal|last1=Maloney |first1=Philip R. |last2=Bland-Hawthorn |first2=J. |title=Warm Gas and Ionizing Photons in the Local Group |journal=The Astrophysical Journal |date=1999 |volume=522 |issue=2 |pages=L81–L84 |doi=10.1086/312223 |arxiv=astro-ph/9907197 |bibcode=1999ApJ...522L..81M }}</ref>
| mass                =  
| mass                = {{val|2.47|0.15|e=12}}<ref name=makarov/>
| luminosity          =  
| luminosity          =  
| flux                =  
| flux                =  
| notes              =  
| notes              =  
| other_names        =  
| other_names        = {{odlist|name=Local Galactic Group |name2=Local group of galaxies| name3=LG |name4=[FWB89] GrG 282 }}<ref name="SIMBAD">{{SIMBAD link|title=Local Group}}</ref>
| names              =  
| names              =  
| references          =SIMBAD
| references          = SIMBAD
}}
}}
[[Image:06-Local Group (LofE06240).png|thumb|A map of the Local Group with two subgroups of both Milky Way and Andromeda galaxies around its center]]
[[Image:VLT Shows Milky Way's Neighbouring Galaxies Have Different History.jpg|thumb|Distribution of the iron content (in logarithmic scale) in four neighbouring dwarf galaxies of the Milky Way]]
[[Image:VLT Shows Milky Way's Neighbouring Galaxies Have Different History.jpg|thumb|Distribution of the iron content (in logarithmic scale) in four neighbouring dwarf galaxies of the Milky Way]]


The '''Local Group''' is the [[galaxy group]] that includes the [[Milky Way]], where [[Earth]] is located. It has a total diameter of roughly {{convert|3|Mpc|e6ly km|lk=on|abbr=off|sigfig=1}},<ref>{{cite journal | last = Redd | first = Nola Taylor | title = Astronomers track dwarf galaxies to better understand the Milky Way's make-up and evolution | journal = Proceedings of the National Academy of Sciences | date = 18 December 2017 | volume = 115 | issue = 51 | pages = 12836–12838 | doi = 10.1073/pnas.1817136115 | pmid = 30568025 | pmc = 6304947 | s2cid = 58645004 | doi-access = free}}</ref> and a total mass of the order of {{convert|2e12|solar mass|kg|lk=in|sigfig=1}}.<ref>The mass of the Local Group is essentially accounted for by the mass of the Milky Way and the Andromeda Galaxy.
The '''Local Group''' is the [[galaxy group]] that includes the [[Milky Way]], where [[Earth]] is located. It consists of two collections of galaxies in a "[[dumbbell]]" shape; the Milky Way and its satellites form one lobe, and the [[Andromeda Galaxy]] and its satellites constitute the other. The two collections are separated by about {{convert|800|kpc|e6ly km|sigfig=1}} and are moving toward one another with a velocity of {{val|123|u=km/s}}.<ref name="Karachentsevetal2006">{{Cite journal |last1=Karachentsev |first1=I. D. |last2=Kashibadze |first2=O. G. |year=2006 |title=Masses of the local group and of the M81 group estimated from distortions in the local velocity field |journal=Astrophysics |volume=49 |issue=1 |pages=3–18 |bibcode=2006Ap.....49....3K |doi=10.1007/s10511-006-0002-6|s2cid=120973010 }}</ref> The [[barycenter|center]] of the group is located at about {{convert|450|kpc|e6ly|abbr=unit|sigfig=2}} away from the Milky Way, placing it slightly closer to the Andromeda Galaxy by roughly {{convert|300|kpc|e6ly|abbr=unit|sigfig=1}}, in which the latter may be more massive than the former in terms of mass.<ref name=makarov/>
 
The Local Group has a total mass of the order of {{convert|2e12|solar mass|kg|lk=in|sigfig=1}},<ref>The mass of the Local Group is essentially accounted for by the mass of the Milky Way and the Andromeda Galaxy.
Estimates for the mass of each galaxy are compatible with {{val|e=12|u={{solar mass}}}},  
Estimates for the mass of each galaxy are compatible with {{val|e=12|u={{solar mass}}}},  
and Peñarrubia et al. (2014) estimate {{val|2.3|0.7|e=12|u={{solar mass}}}} for the Local Group,
and Peñarrubia et al. (2014) estimate {{val|2.3|0.7|e=12|u={{solar mass}}}} for the Local Group,
but Karachentsev and Kashibadze (2006) estimate the somewhat lower value of {{val|1.29|0.14|e=12|u={{solar mass}}}}.</ref>
but Karachentsev and Kashibadze (2006) estimate the somewhat lower value of {{val|1.29|0.14|e=12|u={{solar mass}}}}.</ref> and also a total diameter of {{convert|5.11|Mpc|e6ly km|lk=on|abbr=off|sigfig=2}} based on density matching and the potential surface of its parent structure, [[Local Sheet]].<ref name="marshall2014">{{cite journal |title=A Council of Giants |first=Marshall L. |last=McCall |date=29 April 2013 |publication-date=10 March 2014 |doi=10.1093/mnras/stu199 |journal=Monthly Notices of the Royal Astronomical Society |volume=440 |issue=1 |pages=405–426 |doi-access=free |arxiv=1403.3667 |bibcode=2014MNRAS.440..405M}}</ref> It is itself a part of the [[Local Volume]] and the larger [[Virgo Supercluster]], which is a part of the even greater [[Laniakea Supercluster]] along with the [[Pisces–Cetus Supercluster Complex]]. The exact number of galaxies in the Local Group is unknown, as the Milky Way obscures some; however, a current total of 134 members is known within 1 megaparsec from the center, most of which are [[dwarf galaxies]].<ref name=makarov/> The Local Group was thought to have been more spread in the [[early universe]] with {{convert|7|Mpc|e6ly km|lk=on|abbr=off|sigfig=2}} by 700 million years after the [[Big Bang]].<ref name=boylan>{{cite journal|last1=Boylan-Kolchin |first1=Michael |last2=Weisz |first2=Daniel R. |last3=Bullock |first3=James S. |last4=Cooper |first4=Michael C. |title=The Local Group: The ultimate deep field |journal=Monthly Notices of the Royal Astronomical Society: Letters |date=2016 |volume=462 |pages=L51–L55 |doi=10.1093/mnrasl/slw121 |doi-access=free |arxiv=1603.02679}}</ref>
It consists of two collections of galaxies in a "[[dumbbell]]" shape; the Milky Way and its satellites form one lobe, and the [[Andromeda Galaxy]] and its satellites constitute the other. The two collections are separated by about {{convert|800|kpc|e6ly km|sigfig=1}} and are moving toward one another with a velocity of {{val|123|u=km/s}}.<ref name="Karachentsevetal2006">{{Cite journal |last1=Karachentsev |first1=I. D. |last2=Kashibadze |first2=O. G. |year=2006 |title=Masses of the local group and of the M81 group estimated from distortions in the local velocity field |journal=Astrophysics |volume=49 |issue=1 |pages=3–18 |bibcode=2006Ap.....49....3K |doi=10.1007/s10511-006-0002-6|s2cid=120973010 }}</ref> The group itself is a part of the larger [[Virgo Supercluster]], which may be a part of the [[Laniakea Supercluster]].
The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are [[dwarf galaxies]].


The two largest members, the Andromeda and the Milky Way galaxies, are both [[spiral galaxies]] with masses of about {{val|e=12}} solar masses each. Each has its own system of [[satellite galaxies]]:
The two largest members, the Andromeda and the Milky Way galaxies, are both [[spiral galaxies]] with masses of about {{val|e=12}} solar masses each. Each has its own system of [[satellite galaxies]]:
* The [[List of Andromeda's satellite galaxies|Andromeda Galaxy's satellite system]] consists of [[Messier 32]] (M32), [[Messier 110]] (M110), [[NGC 147]], [[NGC 185]], [[Andromeda I]] (And I), [[And II]], [[And III]], [[And V]], [[And VI]] (also known as the Pegasus Dwarf Spheroidal Galaxy, or Pegasus dSph), [[And VII]] (a.k.a. the Cassiopeia Dwarf Galaxy), [[And VIII]], [[And IX]], [[And X]], [[Andromeda XI|And XI]], [[And XIX]], [[And XXI]] and [[And XXII]], plus several additional [[dwarf galaxy#Ultra-faint dwarf galaxies|ultra-faint]] [[dwarf spheroidal galaxies]].<ref>{{Cite journal |last1=Kalirai |first1=Jason S. |last2=Beaton |first2=Rachael L. |last3=Geha |first3=Marla C.|author3-link= Marla Geha |last4=Gilbert |first4=Karoline M. |last5=Guhathakurta |first5=Puragra |last6=Kirby |first6=Evan N. |last7=Majewski |first7=Steven R. |last8=Ostheimer |first8=James C. |last9=Patterson |first9=Richard J. |date=17 February 2010 |title=The Splash Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, Ii, III, Vii, X, and Xiv Dwarf Spheroidal Galaxies |journal=The Astrophysical Journal  |volume=711 |issue=2 |pages=671–692 |arxiv=0911.1998 |bibcode=2010ApJ...711..671K |doi=10.1088/0004-637X/711/2/671 |s2cid=43188686 |issn=0004-637X}}</ref>
* The [[List of Andromeda's satellite galaxies|Andromeda Galaxy's satellite system]] consists of [[Messier 32]] (M32), [[Messier 110]] (M110), [[NGC 147]], [[NGC 185]], [[Andromeda I]] (And I), [[And II]], [[And III]], [[And V]], [[And VI]] (also known as the Pegasus Dwarf Spheroidal Galaxy, or Pegasus dSph), [[And VII]] (a.k.a. the Cassiopeia Dwarf Galaxy), [[And VIII]], [[And IX]], [[And X]], [[Andromeda XI|And XI]], [[And XIX]], [[And XXI]] and [[And XXII]], plus several additional [[dwarf galaxy#Ultra-faint dwarf galaxies|ultra-faint]] [[dwarf spheroidal galaxies]].<ref>{{Cite journal |last1=Kalirai |first1=Jason S. |last2=Beaton |first2=Rachael L. |last3=Geha |first3=Marla C.|author3-link= Marla Geha |last4=Gilbert |first4=Karoline M. |last5=Guhathakurta |first5=Puragra |last6=Kirby |first6=Evan N. |last7=Majewski |first7=Steven R. |last8=Ostheimer |first8=James C. |last9=Patterson |first9=Richard J. |date=17 February 2010 |title=The Splash Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, Ii, III, Vii, X, and Xiv Dwarf Spheroidal Galaxies |journal=The Astrophysical Journal  |volume=711 |issue=2 |pages=671–692 |arxiv=0911.1998 |bibcode=2010ApJ...711..671K |doi=10.1088/0004-637X/711/2/671 |s2cid=43188686 |issn=0004-637X}}</ref>
* The [[Milky Way's satellite galaxies]] system comprises the [[Sagittarius Dwarf Spheroidal Galaxy|Sagittarius Dwarf Galaxy]], [[Large Magellanic Cloud]], [[Small Magellanic Cloud]], [[Canis Major Dwarf Galaxy]] (disputed, considered by some not a galaxy), [[Ursa Minor Dwarf]] Galaxy, [[Draco Dwarf]] Galaxy, [[Carina Dwarf]] Galaxy, [[Sextans Dwarf Galaxy]], [[Sculptor Dwarf Galaxy]], [[Fornax Dwarf]] Galaxy, [[Leo I (dwarf galaxy)|Leo I]] (a dwarf galaxy), [[Leo II (dwarf galaxy)|Leo II]] (a dwarf galaxy), [[Ursa Major I Dwarf]] Galaxy and [[Ursa Major II Dwarf]] Galaxy, plus several additional ultra-faint dwarf spheroidal galaxies.<ref name="Koposov2015">{{Cite journal |last1=Sergey E. Koposov |last2=Vasily Belokurov |last3=Gabriel Torrealba |last4=N. Wyn Evans |date=10 March 2015 |title=Beasts of the Southern Wild. Discovery of a large number of Ultra Faint satellites in the vicinity of the Magellanic Clouds |journal=The Astrophysical Journal |volume=805 |issue=2 |page=130 |arxiv=1503.02079 |bibcode=2015ApJ...805..130K |doi=10.1088/0004-637X/805/2/130|s2cid=118267222 }}</ref>
* The [[Milky Way's satellite galaxies|Milky Way's satellite system]] comprises the [[Sagittarius Dwarf Spheroidal Galaxy|Sagittarius Dwarf Galaxy]], [[Large Magellanic Cloud]], [[Small Magellanic Cloud]], [[Canis Major Dwarf Galaxy]] (disputed, considered by some not a galaxy), [[Ursa Minor Dwarf]] Galaxy, [[Draco Dwarf]] Galaxy, [[Carina Dwarf]] Galaxy, [[Sextans Dwarf Galaxy]], [[Sculptor Dwarf Galaxy]], [[Fornax Dwarf]] Galaxy, [[Leo I (dwarf galaxy)|Leo I]] (a dwarf galaxy), [[Leo II (dwarf galaxy)|Leo II]] (a dwarf galaxy), [[Ursa Major I Dwarf]] Galaxy and [[Ursa Major II Dwarf]] Galaxy, plus several additional ultra-faint dwarf spheroidal galaxies.<ref name="Koposov2015">{{Cite journal |last1=Sergey E. Koposov |last2=Vasily Belokurov |last3=Gabriel Torrealba |last4=N. Wyn Evans |date=10 March 2015 |title=Beasts of the Southern Wild. Discovery of a large number of Ultra Faint satellites in the vicinity of the Magellanic Clouds |journal=The Astrophysical Journal |volume=805 |issue=2 |page=130 |arxiv=1503.02079 |bibcode=2015ApJ...805..130K |doi=10.1088/0004-637X/805/2/130|s2cid=118267222 }}</ref>


[[File:Local Group Galaxies Comparison.png|thumb|right|350px|Visual size comparison of the six largest Local Group galaxies, with details]]
[[File:Local Group Galaxies Comparison.png|thumb|right|250px|Visual size comparison of the five largest Local Group galaxies along with the possible member [[NGC 3109]], with details]]


The [[Triangulum Galaxy]] (M33) is the third-largest member of the Local Group, with a mass of approximately {{convert|5e10|solar mass|kg|sigfig=1|abbr=on}}, and is the third spiral galaxy.<ref>{{Cite web |url=https://heasarc.gsfc.nasa.gov/docs/cosmic/local_group_info.html |title=The Local Group |website=NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) |publisher=[[NASA]] |access-date=5 May 2015}}</ref> It is unclear whether the Triangulum Galaxy is a companion of the Andromeda Galaxy; the two galaxies are 750,000 light years apart,<ref>{{Cite web|title=Messier Object 33|url=https://www.messier.seds.org/m/m033.html|access-date=2021-05-21|website=www.messier.seds.org}}</ref> and experienced a close passage 2–4&nbsp;billion years ago which triggered star formation across Andromeda's disk. The [[Pisces Dwarf]] Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.<ref name="apj562_2">{{Cite journal |last1=Miller |first1=Bryan W. |last2=Dolphin |first2=Andrew E. |last3=Lee |first3=Myung Gyoon |last4=Kim |first4=Sang Chul |last5=Hodge |first5=Paul |display-authors=1 |date=December 2001 |title=The Star Formation History of LGS 3 |url=http://stacks.iop.org/0004-637X/562/i=2/a=713 |journal=The Astrophysical Journal  |volume=562 |issue=2 |pages=713–726 |arxiv=astro-ph/0108408 |bibcode=2001ApJ...562..713M |doi=10.1086/323853 |s2cid=119089499 |issn=0004-637X}}</ref>
The [[Triangulum Galaxy]] (M33) is the third-largest member of the Local Group, with a mass of approximately {{convert|5e10|solar mass|kg|sigfig=1|abbr=on}}, and is the third spiral galaxy.<ref>{{Cite web |url=https://heasarc.gsfc.nasa.gov/docs/cosmic/local_group_info.html |title=The Local Group |website=NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) |publisher=[[NASA]] |access-date=5 May 2015}}</ref> It is unclear whether the Triangulum Galaxy is a companion of the Andromeda Galaxy; the two galaxies are 750,000 light years apart,<ref>{{Cite web|title=Messier Object 33|url=https://www.messier.seds.org/m/m033.html|access-date=2021-05-21|website=www.messier.seds.org|archive-date=29 June 2023|archive-url=https://web.archive.org/web/20230629151748/http://www.messier.seds.org/m/m033.html|url-status=dead}}</ref> and experienced a close passage 2–4&nbsp;billion years ago which triggered star formation across Andromeda's disk. The [[Pisces Dwarf]] Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.<ref name="apj562_2">{{Cite journal |last1=Miller |first1=Bryan W. |last2=Dolphin |first2=Andrew E. |last3=Lee |first3=Myung Gyoon |last4=Kim |first4=Sang Chul |last5=Hodge |first5=Paul |display-authors=1 |date=December 2001 |title=The Star Formation History of LGS 3 |url=http://stacks.iop.org/0004-637X/562/i=2/a=713 |journal=The Astrophysical Journal  |volume=562 |issue=2 |pages=713–726 |arxiv=astro-ph/0108408 |bibcode=2001ApJ...562..713M |doi=10.1086/323853 |s2cid=119089499 |issn=0004-637X}}</ref>


The other members of the group are likely gravitationally secluded from these large subgroups: [[IC 10]], [[IC 1613]], [[Phoenix Dwarf]] Galaxy, [[Leo A]], [[Tucana Dwarf]] Galaxy, [[Cetus Dwarf]] Galaxy, [[Pegasus Dwarf Irregular Galaxy]], [[Wolf–Lundmark–Melotte]], [[Aquarius Dwarf]] Galaxy, and [[Sagittarius Dwarf Irregular Galaxy]].<ref name=McConnachie>{{Cite journal |last1=McConnachie |first1=Alan W. |year=2012 |title=The observed properties of dwarf galaxies in and around the Local Group |journal=The Astronomical Journal |volume=144 |issue=1 |pages=4 |arxiv=1204.1562 |doi=10.1088/0004-6256/144/1/4|bibcode=2012AJ....144....4M |s2cid=118515618 |url=http://www.astro.uvic.ca/~alan/Nearby_Dwarf_Database.html }}</ref>
The other members of the group are likely gravitationally secluded from these large subgroups: [[IC 10]], [[IC 1613]], [[Phoenix Dwarf]] Galaxy, [[Leo A]], [[Tucana Dwarf]] Galaxy, [[Cetus Dwarf]] Galaxy, [[Pegasus Dwarf Irregular Galaxy]], [[Wolf–Lundmark–Melotte]], [[Aquarius Dwarf]] Galaxy, and [[Sagittarius Dwarf Irregular Galaxy]].<ref name=McConnachie>{{Cite journal |last1=McConnachie |first1=Alan W. |year=2012 |title=The observed properties of dwarf galaxies in and around the Local Group |journal=The Astronomical Journal |volume=144 |issue=1 |pages=4 |arxiv=1204.1562 |doi=10.1088/0004-6256/144/1/4|bibcode=2012AJ....144....4M |s2cid=118515618 |url=http://www.astro.uvic.ca/~alan/Nearby_Dwarf_Database.html }}</ref>


The membership of [[NGC 3109]], with its companions [[Sextans A]] and the [[Antlia Dwarf]] Galaxy as well as [[Sextans B]], [[Leo P]], [[Antlia B]] and possibly [[Leo A]], is uncertain due to extreme distances from the center of the Local Group.<ref name="Karachentsevetal2006" /> The [[Antlia-Sextans Group]] is unlikely to be gravitationally bound to the Local Group due to probably lying outside the Local Group's [[Zero-velocity surface]]—which would make it a true galaxy group of its own rather than a subgroup within the Local Group.<ref>{{cite journal |last1=van den Bergh |first1=Sidney |date=June 1999 |title=The Nearest Group of Galaxies |journal=The Astrophysical Journal |volume=517 |issue=2 |pages=L97–L99 |doi=10.1086/312044 |arxiv=astro-ph/9904425 |bibcode=1999ApJ...517L..97V }}</ref> This possible independence may, however, disappear as the Milky Way continues coalescing with Andromeda due to the increased mass, and density thereof, plausibly widening the radius of the zero-velocity surface of the Local Group.  
The membership of [[NGC 3109]], with its companions [[Sextans A]] and the [[Antlia Dwarf]] Galaxy as well as [[Sextans B]], [[Leo P]], [[Antlia B]] and possibly [[Leo A]], is uncertain due to extreme distances from the center of the Local Group.<ref name="Karachentsevetal2006" /> The [[Antlia-Sextans Group]] is unlikely to be gravitationally bound to the Local Group due to probably lying outside the Local Group's [[zero-velocity surface]]—which would make it a true galaxy group of its own rather than a subgroup within the Local Group.<ref>{{cite journal |last1=van den Bergh |first1=Sidney |date=June 1999 |title=The Nearest Group of Galaxies |journal=The Astrophysical Journal |volume=517 |issue=2 |pages=L97–L99 |doi=10.1086/312044 |arxiv=astro-ph/9904425 |bibcode=1999ApJ...517L..97V }}</ref> This possible independence may, however, disappear as the Milky Way continues coalescing with Andromeda due to the increased mass, and density thereof, plausibly widening the radius of the zero-velocity surface of the Local Group.  


== History ==
== History ==
Line 61: Line 62:


<imagemap>
<imagemap>
Image:Local_Group.svg|frame|center|Local Group (clickable map)
Image:Local_Group.svg|frame|center|Map of the local universe within 5 million light-years from Earth, including the Local Group and other nearby galaxies (clickable map)


rect 392 53 405 72 [[Light-year|ly]]
rect 392 53 405 72 [[Light-year|ly]]
Line 159: Line 160:
| SAcd
| SAcd
| [[Triangulum]]
| [[Triangulum]]
| Third largest, only unbarred spiral galaxy and possible satellite of the Andromeda Galaxy.<br>Diameter (D<sub>25</sub> isophote): 60,000 light-years<br>Mass: {{val|5|e=10|u={{solar mass}} }}<br>Number of stars: {{val|4|e=10}}.
| Third largest, only unbarred spiral galaxy and possible satellite of the Andromeda Galaxy.<br>Diameter (D<sub>25</sub> isophote): 61,100 light-years<br>Mass: {{val|5|e=10|u={{solar mass}} }}<br>Number of stars: {{val|4|e=10}}.
|-
|-
! colspan="4" | [[Magellanic spiral galaxies]]
! colspan="4" | [[Magellanic spiral galaxies]]
Line 166: Line 167:
| Irr/SB(s)m
| Irr/SB(s)m
| [[Dorado]]
| [[Dorado]]
| Fourth largest member of the group, satellite of Milky Way and only Magellanic Spiral Galaxy in the local group<br>Mass: {{val|1|e=10|u={{solar mass}}}}<br>Diameter (D<sub>25</sub> isophote): 32,200 light-years
| Fourth largest known member of the group, satellite of Milky Way and only confirmed Magellanic Spiral Galaxy in the local group<br>Mass: {{val|1|e=10|u={{solar mass}}}}<br>Diameter (D<sub>25</sub> isophote): 32,200 light-years
|-
| [[NGC 3109]] (Antlia Sextans galaxy l)
| SB(s)m
| [[Hydra (constellation)|Hydra]]
| Member of [[Antlia-Sextans Group]]
|-
|-
! colspan="4" | [[Elliptical galaxies]]
! colspan="4" | [[Elliptical galaxies]]
Line 184: Line 180:
| [[Wolf–Lundmark–Melotte]] (WLM, DDO 221)
| [[Wolf–Lundmark–Melotte]] (WLM, DDO 221)
| Ir+
| Ir+
| [[Cetus]]
| [[Cetus (constellation)|Cetus]]
| Possible size between [[Small Magellanic Cloud]] and [[Large Magellanic Cloud]]
| Possible size between [[Small Magellanic Cloud]] and [[Large Magellanic Cloud]]
|-
|-
Line 195: Line 191:
| SB(s)m pec
| SB(s)m pec
| [[Tucana]]
| [[Tucana]]
| Satellite of Milky Way, 6th largest galaxy in the local group
| Satellite of Milky Way, 5th largest known galaxy in the local group<br>Mass: {{val|7|e=9|u={{solar mass}}}}<br>Diameter (D<sub>25</sub> isophote): 18,900 light-years
mass: 7 billion {{solar mass}}
|-
|-
| [[Pisces Dwarf]] (LGS3,Pisces I dwarf irregular)
| [[Pisces Dwarf]] (LGS3,Pisces I dwarf irregular)
Line 205: Line 200:
| [[IC 1613]] (UGC 668, UGCA 47954)
| [[IC 1613]] (UGC 668, UGCA 47954)
| IAB(s)m V
| IAB(s)m V
| [[Cetus]]
| [[Cetus (constellation)|Cetus]]
|
|
|-
|-
Line 288: Line 283:
| dE6p
| dE6p
| Andromeda
| Andromeda
| Satellite of the Andromeda Galaxy and 5th largest galaxy with the mass of 9.3&nbsp;billion solar masses.
| Satellite of the Andromeda Galaxy and the 6th largest galaxy with the mass of 9.3&nbsp;billion solar masses.
|-
|-
| [[NGC 147]] (DDO 3)
| [[NGC 147]] (DDO 3)
Line 358: Line 353:
| Satellite of Milky Way
| Satellite of Milky Way
|-
|-
| [[Sextans Dwarf]](Sextans 1)
| [[Sextans Dwarf]] (Sextans 1)
| dE3
| dE3
| Sextans
| Sextans
Line 873: Line 868:
|-
|-
! colspan=4 | Probable non-members
! colspan=4 | Probable non-members
|-
| [[NGC 3109]] (Antlia Sextans galaxy l)
| SB(s)m
| [[Hydra (constellation)|Hydra]]
| Member of [[Antlia-Sextans Group]], it would be the 4th largest member if part of the Local Group<br>Mass: {{val|2.3|e=9|u={{solar mass}}}}<br>Diameter (D<sub>25.5</sub> isophote): 41,700 light-years
|-
|-
| [[Andromeda IV]]
| [[Andromeda IV]]
Line 994: Line 994:


==Structure==
==Structure==
[[File:Thelocalgroup.jpg|thumb|upright=3|Overview of the structure and trajectory of the Local Group]]
[[File:Thelocalgroup.jpg|thumb|upright=1.7|Overview of the structure and trajectory of the Local Group]]
 
===Streams===
===Streams===
* [[Magellanic Stream]], a stream of gas being stripped off the Magellanic Clouds due to their interaction with the Milky Way
* [[Magellanic Stream]], a stream of gas being stripped off the Magellanic Clouds due to their interaction with the Milky Way
* [[Monoceros Ring]], a ring of stars around the Milky Way that is proposed to consist of a [[stellar stream]] torn from the Canis Major Dwarf Galaxy
* [[Monoceros Ring]], a ring of stars around the Milky Way that is proposed to consist of a [[stellar stream]] torn from the Canis Major Dwarf Galaxy
* Virgo Strem, a steam formed from a dwarf galaxy.
* Virgo Stream, a stream formed from a dwarf galaxy.
* Helni Stream
* Helmi Stream
 
{{clear}}


== Future ==
== Future ==
The galaxies of the Local Group are likely to merge together under their own mutual gravitational attractions over a timescale of [[Timeline of the far future|tens of billions of years]] into a single elliptical galaxy, with the [[Andromeda–Milky Way collision|coalescence of Andromeda and the Milky Way]] being the predominant event in this process.<ref>{{cite journal
{{One source|section|date=November 2025}}
[[File:Andromeda and Milky Way collision.ogv|thumb|upright=1.5|A [[NASA]] conception of the collision using [[computer-generated imagery]]]]
The galaxies of the Local Group are likely to merge together under their own mutual gravitational attractions over a timescale of [[Timeline of the far future|tens of billions of years]] into a single [[elliptical galaxy]], with the [[Andromeda–Milky Way collision|coalescence of Andromeda and the Milky Way]] being the predominant event in this process.<ref>{{cite journal
  | author= Fred C. Adams
  | author= Fred C. Adams
  | author2= Gregory Laughlin
  | author2= Gregory Laughlin
Line 1,016: Line 1,019:
  | arxiv=astro-ph/9701131 | s2cid= 12173790
  | arxiv=astro-ph/9701131 | s2cid= 12173790
  }}</ref>
  }}</ref>
 
There is debate over whether ellipticity might be the immediate structure of the combined galaxy right after the collision or whether ellipticity might only emerge after a theoretical intermediate period of retaining a spiraling structure directly following the collision. Some even theorize a permanent superspiral or a transition toward a more [[lenticular galaxy]], rather than a more elliptical or spiraled distribution, as the future of the Local Group's galactic merger.
[[File:Andromeda and Milky Way collision.ogv|thumb|upright=1.5|A [[NASA]] conception of the collision using [[computer-generated imagery]]]]


== Location ==
== Location ==
{{Main|Laniakea Supercluster}}
{{Main|Laniakea Supercluster}}
{{Excerpt|Laniakea Supercluster|only=paragraph}}
{{Excerpt|Laniakea Supercluster|only=paragraph}}
{{clear}}
{{wide image|Location of Earth (9x1-English Annot-small).png|2000px|A diagram of our location in the [[observable universe]]. (''[[:File:Location of Earth (3x3-English Annot-small).png|Alternative image]].'')}}
{{wide image|Location of Earth (9x1-English Annot-small).png|2000px|A diagram of our location in the [[observable universe]]. (''[[:File:Location of Earth (3x3-English Annot-small).png|Alternative image]].'')}}


Line 1,027: Line 1,030:
* [[Galaxy cluster]]
* [[Galaxy cluster]]
* [[IC 342/Maffei Group]], possibly the group of galaxies nearest to the Local Group
* [[IC 342/Maffei Group]], possibly the group of galaxies nearest to the Local Group
* [[Antlia-Sextans Group]], another candidate for the group of galaxies nearest to the Local Group
* [[List of galaxy groups and clusters]]
* [[List of galaxy groups and clusters]]
* [[List of nearest galaxies]]
* [[Virgocentric flow]]
* [[Virgocentric flow]]


== References ==
== References ==
{{Reflist|2}}
{{Reflist|2}}
== Further reading ==
* {{cite journal | last = Redd | first = Nola Taylor | title = Astronomers track dwarf galaxies to better understand the Milky Way's make-up and evolution | journal = Proceedings of the National Academy of Sciences | date = 18 December 2017 | volume = 115 | issue = 51 | pages = 12836–12838 | doi = 10.1073/pnas.1817136115 | pmid = 30568025 | pmc = 6304947 | s2cid = 58645004 | doi-access = free}}


== External links ==
== External links ==
Line 1,041: Line 1,045:
* {{Cite web |url=http://www2.lowell.edu/users/massey/lgsurvey/ |title=Local Group Galaxies Survey |website=www2.lowell.edu |access-date=12 March 2020}}
* {{Cite web |url=http://www2.lowell.edu/users/massey/lgsurvey/ |title=Local Group Galaxies Survey |website=www2.lowell.edu |access-date=12 March 2020}}
* {{Cite journal |last=van den Bergh |first=Sidney |year=2000 |title=Updated Information on the Local Group |journal=The Publications of the Astronomical Society of the Pacific |volume=112 |issue=770 |pages=529–536 |arxiv=astro-ph/0001040 |bibcode=2000PASP..112..529V |doi=10.1086/316548|s2cid=1805423 }}
* {{Cite journal |last=van den Bergh |first=Sidney |year=2000 |title=Updated Information on the Local Group |journal=The Publications of the Astronomical Society of the Pacific |volume=112 |issue=770 |pages=529–536 |arxiv=astro-ph/0001040 |bibcode=2000PASP..112..529V |doi=10.1086/316548|s2cid=1805423 }}
* {{Cite journal |last1=Pritchet |first1=Christopher J. |last2=Van Den Bergh |first2=Sidney |title=The Luminosity Distribution of Local Group Galaxies |journal=The Astronomical Journal |date=1999 |volume=118 |issue=2 |pages=883–888 |doi=10.1086/300977 |arxiv=astro-ph/9904250 |bibcode=1999AJ....118..883P }}
* {{Cite journal |last1=Teerikorpi |first1=P. |last2=Chernin |first2=A. D. |title=The Hubble diagram for a system within dark energy: The location of the zero-gravity radius and the global Hubble rate |journal=Astronomy and Astrophysics |date=2010 |volume=516 |pages=A93 |doi=10.1051/0004-6361/201014346 |arxiv=1006.0066 |bibcode=2010A&A...516A..93T }}


{{Local Group}}
{{Local Group}}

Latest revision as of 17:07, 15 November 2025

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File:06-Local Group (LofE06240).png
A map of the Local Group with two subgroups of both Milky Way and Andromeda galaxies around its center
File:VLT Shows Milky Way's Neighbouring Galaxies Have Different History.jpg
Distribution of the iron content (in logarithmic scale) in four neighbouring dwarf galaxies of the Milky Way

The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about Template:Convert and are moving toward one another with a velocity of Template:Val.[1] The center of the group is located at about Template:Convert away from the Milky Way, placing it slightly closer to the Andromeda Galaxy by roughly Template:Convert, in which the latter may be more massive than the former in terms of mass.[2]

The Local Group has a total mass of the order of Template:Convert,[3] and also a total diameter of Template:Convert based on density matching and the potential surface of its parent structure, Local Sheet.[4] It is itself a part of the Local Volume and the larger Virgo Supercluster, which is a part of the even greater Laniakea Supercluster along with the Pisces–Cetus Supercluster Complex. The exact number of galaxies in the Local Group is unknown, as the Milky Way obscures some; however, a current total of 134 members is known within 1 megaparsec from the center, most of which are dwarf galaxies.[2] The Local Group was thought to have been more spread in the early universe with Template:Convert by 700 million years after the Big Bang.[5]

The two largest members, the Andromeda and the Milky Way galaxies, are both spiral galaxies with masses of about Template:Val solar masses each. Each has its own system of satellite galaxies:

File:Local Group Galaxies Comparison.png
Visual size comparison of the five largest Local Group galaxies along with the possible member NGC 3109, with details

The Triangulum Galaxy (M33) is the third-largest member of the Local Group, with a mass of approximately Template:Convert, and is the third spiral galaxy.[8] It is unclear whether the Triangulum Galaxy is a companion of the Andromeda Galaxy; the two galaxies are 750,000 light years apart,[9] and experienced a close passage 2–4 billion years ago which triggered star formation across Andromeda's disk. The Pisces Dwarf Galaxy is equidistant from the Andromeda Galaxy and the Triangulum Galaxy, so it may be a satellite of either.[10]

The other members of the group are likely gravitationally secluded from these large subgroups: IC 10, IC 1613, Phoenix Dwarf Galaxy, Leo A, Tucana Dwarf Galaxy, Cetus Dwarf Galaxy, Pegasus Dwarf Irregular Galaxy, Wolf–Lundmark–Melotte, Aquarius Dwarf Galaxy, and Sagittarius Dwarf Irregular Galaxy.[11]

The membership of NGC 3109, with its companions Sextans A and the Antlia Dwarf Galaxy as well as Sextans B, Leo P, Antlia B and possibly Leo A, is uncertain due to extreme distances from the center of the Local Group.[1] The Antlia-Sextans Group is unlikely to be gravitationally bound to the Local Group due to probably lying outside the Local Group's zero-velocity surface—which would make it a true galaxy group of its own rather than a subgroup within the Local Group.[12] This possible independence may, however, disappear as the Milky Way continues coalescing with Andromeda due to the increased mass, and density thereof, plausibly widening the radius of the zero-velocity surface of the Local Group.

History

The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his 1936 book The Realm of the Nebulae.[13] There, he described it as "a typical small group of nebulae which is isolated in the general field" and delineated, by decreasing luminosity, its members to be M31, Milky Way, M33, Large Magellanic Cloud, Small Magellanic Cloud, M32, NGC 205, NGC 6822, NGC 185, IC 1613 and NGC 147. He also identified IC 10 as a possible part of the Local Group.

Component galaxies

Clickable map

Error: Image is invalid or non-existent.

List

Properties of galactic bodies in and around the Local Group[11]
Name Type Constellation Notes
Spiral galaxies
Andromeda Galaxy (M31, NGC 224) SAb Andromeda Largest galaxy in the group[14]
Diameter (D25 isophote): 152,000 light-years
Mass: Template:Val
Number of stars: ca. Template:Val.
Milky Way Galaxy SBbc Sagittarius (centre) Second largest galaxy in the group, which may or may not be the most massive galaxy of the group.[15]
Diameter (D25 isophote): 87,400 light-years
Mass: Template:Val
Number of stars: Template:Val.
Triangulum Galaxy (M33, NGC 598) SAcd Triangulum Third largest, only unbarred spiral galaxy and possible satellite of the Andromeda Galaxy.
Diameter (D25 isophote): 61,100 light-years
Mass: Template:Val
Number of stars: Template:Val.
Magellanic spiral galaxies
Large Magellanic Cloud (LMC, Dorado Dwarf) Irr/SB(s)m Dorado Fourth largest known member of the group, satellite of Milky Way and only confirmed Magellanic Spiral Galaxy in the local group
Mass: Template:Val
Diameter (D25 isophote): 32,200 light-years
Elliptical galaxies
M32 (NGC 221, Andromeda Dwarf) cE2 Andromeda Satellite of the Andromeda Galaxy, shows signs of a supermassive black hole
Irregular galaxies
Wolf–Lundmark–Melotte (WLM, DDO 221) Ir+ Cetus Possible size between Small Magellanic Cloud and Large Magellanic Cloud
IC 10 (Cascopea IV, PGC 4774942-40+4) KBm or Ir+ Cassiopeia Only known starbust galaxy in the Local Group
Small Magellanic Cloud (SMC, NGC 292, Tucana galaxy) SB(s)m pec Tucana Satellite of Milky Way, 5th largest known galaxy in the local group
Mass: Template:Val
Diameter (D25 isophote): 18,900 light-years
Pisces Dwarf (LGS3,Pisces I dwarf irregular) Irr Pisces Possible satellite of the Triangulum Galaxy
IC 1613 (UGC 668, UGCA 47954) IAB(s)m V Cetus
Phoenix Dwarf (Phoenix I dwarf) Irr Phoenix
Leo A (Leo III, PCA QA JO74974) IBm V Leo
Aquarius Dwarf (DDO 210, Aquarius I, ESO 497-4054.4591 G) IB(s)m Aquarius Distance 3.2 million light years. Quite isolated in space, membership to Local Group established in 1999.[16]
SagDIG (Sagittarius Dwarf Irregular Galaxy, Sagittarius II) IB(s)m V Sagittarius Most remote from barycenter member thought to be in the Local Group.[16]
NGC 6822 (Barnard's Galaxy, AO 4797) IB(s)m IV-V Sagittarius
Pegasus Dwarf (Pegasus Dwarf Irregular, DDO 216) Irr Pegasus
UGC 4879 (VV124) IAm Ursa Major One of the most isolated galaxies in Local Group. Situated at the edge of the Local Group.
Sextans A (UGCA 205, AO 4977) Ir+V Sextans Member of Antlia-Sextans Group
Sextans B (UGC 5373, QRT 947748) Ir+IV-V Sextans Member of Antlia-Sextans Group
Leo P (AGC 19470059) Irr Leo Member of Antlia-Sextans Group, extraordinarily low metallicity (Z = 0.03ZMW)
AGC 198606 (Leo VI) Irr? Leo Gas-rich ultra-faint dwarf galaxy
AGC 215417(Leo VII) Irr? Leo Gas-rich ultra-faint dwarf galaxy
AGC 219656 Irr? Leo Gas-rich ultra-faint dwarf galaxy
AGC 249525 Irr? Boötes Gas-rich ultra-faint dwarf galaxy, Situated at the edge of the Local Group
AGC 268069 Irr? Serpens Gas-rich ultra-faint dwarf galaxy
Dwarf elliptical galaxies
M110 (NGC 205) dE6p Andromeda Satellite of the Andromeda Galaxy and the 6th largest galaxy with the mass of 9.3 billion solar masses.
NGC 147 (DDO 3) dE5 pec Cassiopeia Satellite of the Andromeda Galaxy
Dwarf spheroidal galaxies
Boötes I (DDO 9774998.074÷×47) dSph Boötes satellite of the Milky Way
Cetus Dwarf dSph/E4 Cetus 3.4 million light-years away

size:999 light-years

Canes Venatici I Dwarf and Canes Venatici II Dwarf dSph Canes Venatici Satellites of the Milky Way[17][18]
Andromeda III dE2 Andromeda Satellite of the Andromeda Galaxy
NGC 185 dE3 pec Cassiopeia Satellite of the Andromeda Galaxy
Andromeda I dE3 pec Andromeda Satellite of the Andromeda Galaxy
Sculptor Dwarf (E351-G30) dE3 Sculptor Satellite of Milky Way
Andromeda V (UKS 4977-94) dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda II (NCA 14) dE0 Andromeda Satellite of the Andromeda Galaxy
Fornax Dwarf (E356-G04) dSph/E2 Fornax Satellite of Milky Way
Carina Dwarf (E206-G220) dE3 Carina Satellite of Milky Way
Leo I (DDO 74) dE3 Leo Satellite of Milky Way
Sextans Dwarf (Sextans 1) dE3 Sextans Satellite of Milky Way
Leo II (Leo B) dE0 pec Leo Satellite of Milky Way
Ursa Minor Dwarf (NCA 47-49) dE4 Ursa Minor Satellite of Milky Way
Draco Dwarf (DDO 208) dE0 pec Draco Satellite of Milky Way
SagDSG (Sagittarius Dwarf Spheroidal Galaxy) dSph/E7 Sagittarius Satellite of Milky Way
Tucana Dwarf dE5 Tucana 3.2 million ly away
Cassiopeia Dwarf (Andromeda VII, NCA 4) dSph Cassiopeia Satellite of the Andromeda Galaxy
Pegasus Dwarf Spheroidal Galaxy (Andromeda VI) dSph Pegasus Satellite of the Andromeda Galaxy
Ursa Major I Dwarf dSph Ursa Major Satellite of the Milky Way
Ursa Major II Dwarf dSph Ursa Major Satellite of the Milky Way
Ursa Major III dSph Ursa Major Satellite of the Milky Way
Leo IV dSph Leo Satellite of the Milky Way
Leo V dSph Leo Satellite of the Milky Way
Leo T dSph/Irr Leo Satellite of the Milky Way
Boötes II dSph Boötes Satellite of the Milky Way
Boötes III (NCA 4.9) dSph Boötes Satellite of the Milky Way, Bootes lll likely formed both the Bootes Ill Stream & the Monosoros Stellar stream
Boötes IV dSph Boötes Satellite of the Milky Way
Coma Berenices dSph Coma Berenices Satellite of the Milky Way
Segue 2 (Aries Dwarf, NCA 429) dSph Aries Satellite of the Milky Way

size:220 light-years number of stars:≈1000

Hercules (NCA 4977429) dSph Hercules Satellite of the Milky Way
Pisces II dSph Pisces Satellite of the Milky Way
Reticulum II dSph Reticulum Satellite of the Milky Way
Reticulum III dSph Reticulum Satellite of the Milky Way
Eridanus II dSph Eridanus Probable satellite of the Milky Way
Grus I dSph Grus Satellite of the Milky Way
Grus II dSph Grus Satellite of the Milky Way
Tucana II dSph Tucana Satellite of the Milky Way
Hydrus I (Hydrus Dwarf spheroidal galaxy) dSph Hydrus Satellite of the Milky Way
Draco II dSph Draco Satellite of the Milky Way
Carina III dSph Carina Satellite of the Milky Way
Triangulum II (Laevens 2) dSph Triangulum Satellite of the Milky Way
Carina II dSph Carina Satellite of the Milky Way
Pictor II dSph Pictor Satellite of the Milky Way
Horologium II dSph Horologium Satellite of the Milky Way
Virgo I dSph Virgo Satellite of the Milky Way
Virgo III dSph? Virgo Satellite of the Milky Way[19]
Sextans II dSph? Sextans Satellite of the Milky Way[19]
Aquarius II dSph Aquarius Satellite of the Milky Way
Aquarius III dSph? Aquarius Satellite of the Milky Way[20]
Crater II dSph Crater Satellite of the Milky Way
Hydra II dSph Hydra Satellite of the Milky Way
Antlia II dSph Antlia Satellite of the Milky Way
Pegasus III dSph Pegasus Satellite of the Milky Way
Pegasus IV dSph Pegasus Satellite of the Milky Way[21]
Pegasus W dSph Pegasus Recent star formation, could still be starforming
Cetus III dSph Cetus Satellite of the Milky Way
Leo K dSph? Leo Satellite of the Milky Way[22]
Leo M dSph? Leo Satellite of the Milky Way[22]
Leo VI dSph Leo Satellite of the Milky Way[23]
Leo Minor I dSph? Leo Minor Satellite of the Milky Way[24]
Boötes V dSph? Boötes Satellite of the Milky Way[24]
Virgo II dSph? Virgo Satellite of the Milky Way[24]
Tucana B dSph Tucana [25]
DES 1 dE Perseus Satellite of Milky Way
Antlia Dwarf dE3/dSph/Irr? Antlia Member of Antlia-Sextans Group
Andromeda IX dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda X dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XI dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XII dSph Andromeda Possible satellite of the Andromeda Galaxy
Andromeda XIII (Pisces III) dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XIV (Pisces IV) dSph Pisces Possible satellite of the Andromeda Galaxy
Andromeda XV dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XVII dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XIX dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XX dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXI dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXII dSph Pisces Possible satellite of the Triangulum Galaxy
Andromeda XXIII dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXIV dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXV dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXVI dSph Andromeda Satellite of the Andromeda Galaxy
Andromeda XXVII dSph Andromeda Satellite of the Andromeda Galaxy, tidally disrupted[26]
Andromeda XXIX dSph Pegasus Satellite of the Andromeda Galaxy
Andromeda XXX (Cassiopeia II) dSph? Cassiopeia Satellite of the Andromeda Galaxy
Andromeda XXXI (Lacerta I) dSph? Lacerta Satellite of the Andromeda Galaxy
Andromeda XXXII (Cassiopeia III) dSph? Cassiopeia Satellite of the Andromeda Galaxy
Andromeda XXXIV (Pegasus V) dSph Pegasus Satellite of the Andromeda Galaxy[27]
Andromeda XXXV dSph Andromeda Satellite of the Andromeda Galaxy[28]
Andromeda XVI (Pisces V) dSph Pisces Possible satellite of the Andromeda Galaxy
Andromeda XXVIII dSph? Pegasus Possible satellite of the Andromeda Galaxy
Andromeda XXXIII (Perseus I) dSph? Perseus Possible satellite of the Andromeda Galaxy
Andromeda XVIII dSph Andromeda
Centaurus I dSph Centaurus Satellite of the Milky Way[29]
Pisces VII (Triangulum III) dSph? Pisces Candidate, possible satellite of the Triangulum Galaxy[30]
Identification unclear
Virgo Stellar Stream dSph (remnant)? Virgo In the process of merging with the Milky Way
Canis Major Dwarf Irr? Canis Major Possibly a dwarf galaxy in the process of merging with the Milky Way
Hydra 1 Hydra Possibly a dwarf galaxy in the process of merging with the Milky Way
Tucana III dSph or cluster? Tucana Satellite of the Milky Way, tidally disrupting
Tucana IV dSph or cluster? Tucana Satellite of the Milky Way
Tucana V dSph or cluster? Tucana Possibly non-existent
Columba I dSph or cluster? Columba Satellite of the Milky Way
Segue 1 dSph or Globular Cluster Leo Satellite of the Milky Way
Cetus II Cetus Likely part of Sagittarius tidal stream
Willman 1 dSph or Globular Cluster Ursa Major 147,000 light-years away
Horologium I dSph or Globular Cluster Horologium Satellite of the Milky Way. Not to be confused with the Horologium Supercluster.
Pictoris dSph or Globular Cluster Pictor Satellite of the Milky Way
Phoenix II dSph or Globular Cluster Phoenix Satellite of the Milky Way
Indus I (Kim 2, Indus Dwarf) dSph or Globular Cluster Indus Satellite of the Milky Way
Eridanus III dSph or Globular Cluster Eridanus Satellite of the Milky Way or SMC[31]
Sagittarius II dSph or Globular Cluster Sagittarius Satellite of the Milky Way
Andromeda VIII (Adsant-40-7 quote serp galaxy) dSph? Andromeda Satellite of the Andromeda Galaxy, tidally disrupting
Antlia B Antlia Member of Antlia-Sextans Group
Probable non-members
NGC 3109 (Antlia Sextans galaxy l) SB(s)m Hydra Member of Antlia-Sextans Group, it would be the 4th largest member if part of the Local Group
Mass: Template:Val
Diameter (D25.5 isophote): 41,700 light-years
Andromeda IV Irr Andromeda Once considered to be associated with M31. Its distance is now known to be 22 to 24 million light years (not close to the Andromeda Galaxy at all).[32]
GR 8 (DDO 155) Im V Virgo Distance 7.9 million light years[33]
IC 5152 (Indus III) IAB(s)m IV Indus Distance 5.8 million light years, possibly an outlying member of the Local Group[34]
KK 153 Ursa Major Distance 6.5 million light years, possibly an outlying member of the Local Group[35]
NGC 300 SA(s)d Sculptor Distance 6.07 million light years
NGC 55 SB(s)m Sculptor Distance 6.5 million light years[36]
NGC 404 E0 or SA(s)0− Andromeda Distance 10 million light years[37]
NGC 1569 (IC 49447) Irp+ III-IV Camelopardalis In IC 342 group of galaxies. Distance 11 million light years[38]
NGC 1560 (IC 2062) Sd Camelopardalis Distance 8-12 million light years
Camelopardalis A Irr Camelopardalis Distance 12 million light years[36]
Argo Dwarf Irr Carina 7.1 million light-years away
ESO 347-8 (2318–42, PGC 475744) Irr Grus 9 million light-years away fairly isolated until million light years. away from the galaxy
UKS 2323-326 (ESO 407-18) Irr Sculptor Distance 7.2 million light-years[36]
UGC 9128 (DDO 187) Irp+ Boötes 7 million light-years away
KKs 3 (Hydrus II) dSph Hydrus Distance 5.2 million light-years
Objects in the Local Group no longer recognised as galaxies
Palomar 12 (Capricornus Dwarf) dSphr Capricornus Globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 4 (Ursa Major Dwarf) d Sphr Ursa Major Globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 5 (Serpens Dwarf) Serpens Globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 3 (Sextans C) Sculptor Globular cluster formerly classified as a dwarf spheroidal galaxy[39]
Segue 3 Pegasus Globular cluster formerly classified as a dwarf spheroidal galaxy[40]
Laevens 1 (Crater Dwarf) Crater Globular cluster formerly classified as a dwarf spheroidal galaxy[41]
DES J2038-4609 (Indus II) Indus Likely a chance alignment of stars[42]
Name Type Constellation Notes

Structure

File:Thelocalgroup.jpg
Overview of the structure and trajectory of the Local Group

Streams

  • Magellanic Stream, a stream of gas being stripped off the Magellanic Clouds due to their interaction with the Milky Way
  • Monoceros Ring, a ring of stars around the Milky Way that is proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy
  • Virgo Stream, a stream formed from a dwarf galaxy.
  • Helmi Stream

Future

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File:Andromeda and Milky Way collision.ogv
A NASA conception of the collision using computer-generated imagery

The galaxies of the Local Group are likely to merge together under their own mutual gravitational attractions over a timescale of tens of billions of years into a single elliptical galaxy, with the coalescence of Andromeda and the Milky Way being the predominant event in this process.[43] There is debate over whether ellipticity might be the immediate structure of the combined galaxy right after the collision or whether ellipticity might only emerge after a theoretical intermediate period of retaining a spiraling structure directly following the collision. Some even theorize a permanent superspiral or a transition toward a more lenticular galaxy, rather than a more elliptical or spiraled distribution, as the future of the Local Group's galactic merger.

Location

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See also

References

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Further reading

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External links

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  3. ↑ The mass of the Local Group is essentially accounted for by the mass of the Milky Way and the Andromeda Galaxy. Estimates for the mass of each galaxy are compatible with Template:Val, and Peñarrubia et al. (2014) estimate Template:Val for the Local Group, but Karachentsev and Kashibadze (2006) estimate the somewhat lower value of Template:Val.
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