| Cygnus A | |
|---|---|
 False-color radio image at 5 GHz (VLA data) | |
| Observation data (J2000epoch) | |
| Constellation | Cygnus |
| Right ascension | 19h 59m 28.3566s[1] |
| Declination | +40° 44′ 02.096″[1][2] |
| Redshift | 0.056075 ± 0.000067[1][2] |
| Distance | 232 Mpc (760 million ly)[3] |
| Group orcluster | Cygnus-A-Cluster |
| Apparent magnitude (V) | 16.22[1][2] |
| Characteristics | |
| Type | E[1][2] |
| Apparent size (V) | 0.549' × 0.457'[1][2] |
| Other designations | |
| 4C 40.40,2E 4309, CYG A, W 57, BWE 1957+4035,NRAO 620,1C 19.01,QSO B1957+405,3C 405,1RXS J195928.7+404405,3C 405.0,2U 1957+40,3CR 405,LEDA 63932,4U 1957+40,VV2000c J195928.3+404402,DA 500,MCG+07-41-003,DB 117,Mills 19+4,VV 72,[1] PGC 63932. | |
Cygnus A (3C 405) is aradio galaxy, one of the strongestradio sources in the sky.
A concentrated radio source in Cygnus was discovered byGrote Reber in 1939. In 1946Stanley Hey and his colleague James Phillips identified that the sourcescintillated rapidly, and must therefore be a compact object.[4] In 1951, Cygnus A, along withCassiopeia A, andPuppis A were the first "radio sources" identified with an optical instrument. Of these, Cygnus A became the first radio galaxy, the other two beingnebulae inside theMilky Way.[5] In 1953Roger Jennison andM K Das Gupta showed it to be a double source.[6] Like all radio galaxies, it contains anactive galactic nucleus (AGN). Thesupermassive black hole at the core has a mass of(2.5±0.7)×109 M☉.[3]Jets from the AGN have also been observed to induce hotspots in theradio lobes and subsequently holes in the surroundIntergalactic medium (IGM).[7]
Cygnus A is thecD galaxy in a richgalaxy cluster of the same name, and has been found to have quite a number of around 200 neighboring galaxies.[8] It is also worth to note that the larger Cygnus galaxy cluster is undergoing a clustermerger, of which it is one of the first cluster mergers whoseradial velocity (Doppler Shift) has been measured throughX-ray spectroscopy.[9]
Images of the galaxy in theradio portion of theelectromagnetic 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 atvisible wavelengths.[10] 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 surroundingintergalactic medium.[11]
These hotspots interacting with theintergalactic medium, orintracluster medium (ICM), primarily observed in the radio spectrum can also be observed in the X-Ray range.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.[7]X-Ray jets thermally heat these hotspots, energizing them and pushing surrounding plasma out of the way carving a hole through the ICM.[12] The most prominent cavity is seen in the eastern lobe (on the left) where the diameter of the hole is around 3900parsecs, or around 11,700 lightyears wide, and the depth is 13.3 kiloparsecs, or 44,000lightyears deep.[7]
Although it has not been directly observed, Cygnus A's spectra suggest there is a dustytorus 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.[13]
In 2016, a radiotransient 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 radioflux density, with comparable luminosity to the brightest knownsupernova. 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 asecond supermassive black hole orbiting the primary object, with the secondary having undergone a rapidaccretion 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.[14]
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