View source for Cygnus A

{{short description|Radio galaxy}}
{{Infobox Galaxy
| name = Cygnus A
| image = 3c405.jpg
| image_scale = 1.2
| caption = [[False-color]] radio image at 5 GHz ([[Very Large Array|VLA]] data)
| epoch = [[J2000]]
| ra = {{RA|19|59|28.3566}}<ref name="ned">{{cite web
  | work=NASA/IPAC Extragalactic Database
  | title=Results for Cygnus A
  | url=http://nedwww.ipac.caltech.edu/cgi-bin/objsearch?objname=Cygnus+A&extend=no
  | access-date=2008-10-01}}</ref>
| dec = {{DEC|+40|44|02.096}}<ref name="ned" /><ref name="simbad">{{cite simbad
  | title =NAME Cygnus A
  | access-date =2016-02-29}}</ref>   
| constellation name = [[Cygnus (constellation)|Cygnus]]
| z = 0.056075 ± 0.000067<ref name="ned" /><ref name="simbad" />
| dist_ly = {{Convert|232|Mpc|e6ly|abbr=unit}}<ref name=Graham2008/>
| group_cluster = Cygnus-A-Cluster
| type = E<ref name="ned" /><ref name="simbad" />
| appmag_v = 16.22<ref name="ned" /><ref name="simbad" />
| size_v = 0.549' × 0.457'<ref name="ned" /><ref name="simbad" />
| notes =
| names = [[Fourth Cambridge Survey|4C]] 40.40, [[Einstein Observatory|2E]] 4309, CYG A, W 57, BWE 1957+4035, [[NRAO]] 620, [[First Cambridge Catalogue of Radio Sources|1C]] 19.01, [[Quasar|QSO]] B1957+405, [[Third Cambridge Catalogue of Radio Sources|3C]] 405, [[1RXS]] J195928.7+404405, [[Third Cambridge Catalogue of Radio Sources|3C]] 405.0, [[2U (astronomical catalog)|2U]] 1957+40, [[Third Cambridge Catalogue of Radio Sources|3CR]] 405, [[Lyon-Meudon Extragalactic Database|LEDA]] 63932, [[4U (astronomical catalogue)|4U]] 1957+40, [[VV2000c]] J195928.3+404402, [[List of astronomical catalogues#D|DA]] 500, [[Morphological Catalogue of Galaxies|MCG]]+07-41-003, [[DB (astronomical catalog)|DB]] 117, [[Mills (astronomical catalog)|Mills]] 19+4, [[Atlas of Interacting Galaxies|VV]] 72,<ref name="ned" /> PGC 63932.
}}
'''Cygnus A''' ([[Third Cambridge Catalogue of Radio Sources|3C]] 405) is a [[radio galaxy]], one of the strongest [[astronomical radio source|radio sources]] in the sky.

== Discovery and Identification ==
A concentrated radio source in Cygnus was discovered by [[Grote Reber]] in 1939. In 1946 [[James Stanley Hey|Stanley Hey]] and his colleague James Phillips identified that the source [[twinkling|scintillated]] rapidly, and must therefore be a compact object.<ref>{{cite journal | doi=10.1098/rspa.1948.0017 | title=An investigation of galactic radiation in the radio spectrum | journal=Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences | year=1948 | volume=192 | issue=1030 | pages=425–445 | bibcode=1948RSPSA.192..425H | last1=Hey | first1=J. S. | last2=Parsons | first2=S. J. | last3=Phillips | first3=J. W. | s2cid=121054928 }}</ref> In 1951, Cygnus A, along with [[Cassiopeia A]], and [[Puppis A]] were the first "radio sources" identified with an optical instrument. Of these, Cygnus A became the first radio galaxy, the other two being [[nebula]]e inside the [[Milky Way]].<ref name=ApJ-1954-01>{{cite journal | doi=10.1086/145812 | title=Identification of the Radio Sources in Cassiopeia, Cygnus a, and Puppis A | year=1954 | last1=Baade | first1=W. | last2=Minkowski | first2=R. | journal=The Astrophysical Journal | volume=119 | page=206 | bibcode=1954ApJ...119..206B }}</ref> In 1953 [[Roger Clifton Jennison|Roger Jennison]] and [[Mrinal Kumar Das Gupta|M K Das Gupta]] showed it to be a double source.<ref>{{cite journal
  | author1=Jennison, R.C.
  | author2=Das Gupta, M.K.
  | title=Fine Structure of the extra-terrestrial radio source Cygnus 1
  | journal=Nature
  | page=996
  | year=1953
  | volume=172
 | issue=4387
 | doi=10.1038/172996a0
 | bibcode=1953Natur.172..996J
 | s2cid=4251058
 | url=http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1953Natur.172..996J&amp;db_key=AST
  | archive-url=https://web.archive.org/web/20190827000433/http://ukads.nottingham.ac.uk/cgi-bin/nph-bib_query?bibcode=1953Natur.172..996J&amp;db_key=AST
  | url-status=dead
  | archive-date=August 27, 2019
  | url-access=subscription
  }}</ref> Like all radio galaxies, it contains an [[active galactic nucleus]] (AGN). The [[supermassive black hole]] at the core has a mass of {{Val|2.5e9|.7|ul=solar mass}}.<ref name=Graham2008>{{cite journal
 | title=Populating the Galaxy Velocity Dispersion - Supermassive Black Hole Mass Diagram: A Catalogue of (Mbh, σ) Values
 | last1=Graham | first1=Alister W.
 | journal=Publications of the Astronomical Society of Australia
 | volume=25 | issue=4 | pages=167–175 | date=November 2008
 | doi=10.1071/AS08013 | bibcode=2008PASA...25..167G |arxiv = 0807.2549 | s2cid=89905 }}</ref> [[Astrophysical jet|Jets]] from the AGN have also been observed to induce hotspots in the [[Main lobe|radio lobes]] and subsequently holes in the surround [[Outer space#Intergalactic space|Intergalactic medium]] (IGM).<ref name=":0" />

Cygnus A is the [[cD galaxy]] in a rich [[galaxy cluster]] of the same name, and has been found to have quite a number of around 200 neighboring galaxies.<ref name=":02">{{Cite journal |last=Ledlow, Owen, and Miller |date=July 2005 |title=The Cluster of Galaxies Surrounding Cygnus A. II. New Velocities and a Dynamic Model |url=https://iopscience.iop.org/article/10.1086/430628/pdf |journal=The Astrophysical Journal |volume=130 |issue=1 |pages=47–54 |arxiv=astro-ph/0503581 |bibcode=2005AJ....130...47L |doi=10.1086/430628}}</ref> It is also worth to note that the larger Cygnus galaxy cluster is undergoing a cluster [[Galaxy merger|merger]], of which it is one of the first cluster mergers whose [[radial velocity]] ([[Doppler spectroscopy|Doppler Shift]]) has been measured through [[X-ray spectroscopy]].<ref name=":1">{{Citation |last1=Sarazin |first1=Craig L. |title=Merger shocks in Abell 3667 and the Cygnus a cluster |date=2012-11-20 |journal=Astronomische Nachrichten |volume=334 |issue=4–5 |pages=346–349 |arxiv=1211.4823 |doi=10.1002/asna.201211854 |last2=Finoguenov |first2=Alexis |last3=Wik |first3=Daniel R.}}</ref>

== Jets and Hotspots ==
Images of the galaxy in the [[Radio wave|radio]] portion of the [[electromagnetic spectrum]] show two jets protruding in opposite directions from the galaxy's center. These jets extend many times the width of the portion of the host galaxy which emits radiation at [[Visible spectrum|visible wavelengths]].<ref>{{cite web
  | author=Strange, D
  | title=The Radio Galaxy Cygnus "A"
  | url=http://ourworld.compuserve.com/homepages/dstrange/cygnusa.htm
  | access-date=2008-09-22
  | url-status=dead
  | archive-url=https://web.archive.org/web/20080725125333/http://ourworld.compuserve.com/homepages/dstrange/cygnusa.htm
  | archive-date=July 25, 2008
  }}</ref> At the ends of the jets are two lobes with "hot spots" of more intense radiation at their edges. These hot spots are formed when material from the jets collides with the surrounding [[Outer space|intergalactic medium]].<ref>{{cite web
  |author1=Nemiroff, Robert |author-link1 = Robert J. Nemiroff |author2=Bonnell, Jerry | title= X-Ray Cygnus A
  | work=Astronomy Picture of the Day
  | date=2002-10-05
  | url=http://www.sai.msu.su/apod/ap021005.html
  | access-date=2008-09-22}}</ref>  

These hotspots interacting with the [[intergalactic medium]], or [[intracluster medium]] (ICM), primarily observed in the radio spectrum can also be observed in the X-Ray range. [[Chandra X-ray Observatory|Chandra's]] resolution in the X-Ray range gave the resolution and wavelength necessary to observe the hotspots in better detail, and they turned out to be cavity or hole like structures in both lobes. The cavities seen carved out at the hotspots of lobes are caused by the interaction between the jets, powered by the AGN of Cygnus A, and the intra-cluster-medium surrounding the galaxy.<ref name=":0">{{Citation |last1=Snios |first1=Bradford |title=The X-Ray Cavity Around Hotspot e in Cygnus A: Tunneled by a Deflected Jet |date=2020-03-03 |url=https://arxiv.org/abs/2002.02978 |access-date=2025-02-18 |arxiv=2002.02978 |last2=Johnson |first2=Amalya C. |last3=Nulsen |first3=Paul E. J. |last4=Kraft |first4=Ralph P. |last5=Vries |first5=Martijn de |last6=Perley |first6=Richard A. |last7=Sebokolodi |first7=Lerato |last8=Wise |first8=Michael W.|journal=The Astrophysical Journal |volume=891 |issue=2 |page=173 |doi=10.3847/1538-4357/ab737d |doi-access=free |bibcode=2020ApJ...891..173S }}</ref> [[Astrophysical X-ray source|X-Ray jets]] thermally heat these hotspots, energizing them and pushing surrounding plasma out of the way carving a hole through the ICM.<ref>{{Citation |last1=Marcowith |first1=A. |title=The microphysics of collisionless shock waves |date=2016-04-01 |url=https://arxiv.org/abs/1604.00318 |access-date=2025-02-18 |arxiv=1604.00318 |last2=Bret |first2=A. |last3=Bykov |first3=A. |last4=Dieckman |first4=M. E. |last5=Drury |first5=L. O. C. |last6=Lembege |first6=B. |last7=Lemoine |first7=M. |last8=Morlino |first8=G. |last9=Murphy |first9=G.|journal=Reports on Progress in Physics |volume=79 |issue=4 |page=046901 |doi=10.1088/0034-4885/79/4/046901 |pmid=27007555 |bibcode=2016RPPh...79d6901M }}</ref> The most prominent cavity is seen in the eastern lobe (on the left) where the diameter of the hole is around 3900 [[Parsec|parsecs]], or around 11,700 lightyears wide, and the depth is 13.3 kiloparsecs, or 44,000 [[Light-year|lightyears]] deep.<ref name=":0" />

Although it has not been directly observed, Cygnus A's spectra suggest there is a dusty [[torus]] obscuring the AGN centered on the jet's axis. The torus has been observed to extend around 200 pc radially outwards from the center with an estimated height of 143 pc.<ref>{{Cite journal |last1=Carilli |first1=C. L. |last2=Perley |first2=R. A. |last3=Dhawan |first3=V. |last4=Perley |first4=D. A. |date=2019-04-05 |title=Imaging the Active Galactic Nucleus Torus in Cygnus A |journal=The Astrophysical Journal |volume=874 |issue=2 |pages=L32 |doi=10.3847/2041-8213/ab1019 |doi-access=free |arxiv=1904.01365 |bibcode=2019ApJ...874L..32C |issn=2041-8213}}</ref>[[File:Cygnus A composite.jpg|thumb|300x300px|Cygnus A composite image of X-Ray light from Chandra Space Telescope (blue) and radio from NSF's Very Large Array (red). Notice the bright hotspots in the eastern and western lobes lit up in both red and blue.]]

== Second Black hole ==
In 2016, a radio [[transient astronomical event|transient]] was discovered 460 parsecs away from the center of Cygnus A. Between 1989 and 2016, the object, cospatial with a previously-known infrared source, exhibited at least an eightfold increase in radio [[flux density]], with comparable luminosity to the brightest known [[supernova]]. Due to the lack of measurements in the intervening years, the rate of brightening is unknown, but the object has remained at a relatively constant flux density since its discovery. The data are consistent with a [[binary black hole|second supermassive black hole]] orbiting the primary object, with the secondary having undergone a rapid [[Accretion (astrophysics)|accretion]] rate increase. The inferred orbital timescale is of the same order as the activity of the primary source, suggesting the secondary may be perturbing the primary and causing the outflows.<ref name="PerleyPerley2017">{{cite journal|last1=Perley|first1=D. A.|last2=Perley|first2=R. A.|last3=Dhawan|first3=V.|last4=Carilli|first4=C. L.|title=Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A|journal=The Astrophysical Journal|volume=841|issue=2|year=2017|pages=117|issn=1538-4357|doi=10.3847/1538-4357/aa725b|arxiv = 1705.07901 |bibcode = 2017ApJ...841..117P |s2cid=54536121 |doi-access=free }}</ref>

== See also ==
* [[List of galaxies]]
* [[List of nearest galaxies]]

== References ==

<references/>

==Further reading==
* {{cite journal |bibcode=1994Natur.367..713H|title=X-ray emission from the radio hotspots of Cygnus A |last1=Harris |first1=D. E. |last2=Carilli |first2=C. L. |last3=Perley |first3=R. A. |journal=Nature |year=1994 |volume=367 |issue=6465 |page=713 |doi=10.1038/367713a0 |s2cid=4352349 }}
*{{cite web
  | title=Cygnus A
  | work=SIMBAD Astronomical Database
  | url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=Cygnus+A&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id}} 
*{{cite web
  | author=Blanco, Philip
  | title=The powerful radio galaxy Cygnus A
  | date=1997-02-07
  | url=http://mamacass.ucsd.edu/people/pblanco/cyga.html
  | url-status=dead
  | archive-url=https://archive.today/20120210140951/http://mamacass.ucsd.edu/people/pblanco/cyga.html
  | archive-date=2012-02-10
  }}
*{{cite web |last1=Tuesday |first1=Alison Klesman |date=May 2017 |title=A familiar galaxy with a new surprise: Two supermassive black holes |url=https://astronomy.com/news/2017/05/galaxy-with-two-supermassive-black-holes |website=Astronomy.com |language=en}}

== External links ==
{{commonscat}}
*[http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=cygnus+a&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2005&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0 Information about Cygnus A] from SIMBAD.
*[http://hubblesite.org/newscenter/archive/releases/1994/1994/42/text/ Hubble Uncovers a Hidden Quasar in a Nearby Galaxy (Cygnus A)]
*[https://www.g4fas.net/1998-07-07-Cygnus-A-night-of-nights.html A primitive transit recording (7 July 1998) of Cygnus A by English radio amateur Geoff Royle G4FAS]

{{Stars of Cygnus}}
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[[Category:3C objects|405.0]]
[[Category:Cygnus (constellation)]]
[[Category:Radio galaxies]]
[[Category:Quasars]]
[[Category:Astronomical objects discovered in 1939]]