Cygnus A

Cygnus A (3C 405) is a radio galaxy, and one of the strongest radio sources in the sky. It was discovered by Grote Reber in 1939. In 1951, Cygnus A, along with Cassiopeia A, and Puppis A were the first "radio stars" identified with an optical source. Of these, Cygnus A became the first radio galaxy; the other two being nebulae inside the Milky Way.[4] In 1953 Roger Jennison and M K Das Gupta showed it to be a double source.[5] Like all radio galaxies, it contains an active galactic nucleus. The super massive black hole at the core has a mass of (2.5±0.7)×109 M.[3]

Images of the galaxy in the 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 wavelengths.[6] 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 intergalactic medium.[7]

In 2016, a radio 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 second supermassive black hole orbiting the primary object, with the secondary having undergone a rapid 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.[8]

Cygnus A
3c405
Observation data (J2000 epoch)
ConstellationCygnus
Right ascension 19h 59m 28.3566s[1]
Declination+40° 44′ 02.096″[1][2]
Redshift0.056075 ± 0.000067[1][2]
Distance232[3] Mpc
Apparent magnitude (V)16.22[1][2]
Characteristics
TypeE[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.

References

  1. ^ a b c d e f g "Results for Cygnus A". NASA/IPAC Extragalactic Database. Retrieved 2008-10-01.
  2. ^ a b c d e "NAME Cygnus A". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-02-29.
  3. ^ a b Graham, Alister W. (November 2008), "Populating the Galaxy Velocity Dispersion - Supermassive Black Hole Mass Diagram: A Catalogue of (Mbh, σ) Values", Publications of the Astronomical Society of Australia, 25 (4): 167–175, arXiv:0807.2549, Bibcode:2008PASA...25..167G, doi:10.1071/AS08013.
  4. ^ Astrophysical Journal, "Identification of the Radio Sources in Cassiopeia (A), Cygnus A, and Puppis A", Baade, W.; Minkowski, R., vol. 119, p.206, January 1954, doi:10.1086/145812 , Bibcode1954ApJ...119..206B
  5. ^ Jennison, R.C.; Das Gupta, M.K. (1953). "Fine Structure of the extra-terrestrial radio source Cygnus 1". Nature, Vol. 172. p. 996.
  6. ^ Strange, D. "The Radio Galaxy Cygnus "A"". Archived from the original on July 25, 2008. Retrieved 2008-09-22.
  7. ^ Nemiroff, Robert; Bonnell, Jerry (2002-10-05). "X-Ray Cygnus A". Astronomy Picture of the Day. Retrieved 2008-09-22.
  8. ^ Perley, D. A.; Perley, R. A.; Dhawan, V.; Carilli, C. L. (2017). "Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A". The Astrophysical Journal. 841 (2): 117. arXiv:1705.07901. Bibcode:2017ApJ...841..117P. doi:10.3847/1538-4357/aa725b. ISSN 1538-4357.

A second massive black hole has been discovered in galaxy Cygnus A (Astronomy magazine, September 2017).

External links

52 Cygni

52 Cygni is a giant star in the northern constellation of Cygnus with an apparent magnitude of 4.22. Based on its Hipparcos parallax, it is about 291 light-years (89 pc) away.

52 Cygni is a probable horizontal branch (red clump) star, fusing helium in its core, although there is a 25% chance that it is still on the red giant branch (RGB) and fusing hydrogen in a shell around an insert core. As a clump giant it would be 2.27 gyr old, but only 910 myr if it is an RGB star. It shines with a bolometric luminosity of about 90 L☉ at an effective temperature of 4,677 K. It has a radius of about 14 R☉.At an angular separation of 6.0″ from 52 Cygni is a faint magnitude 9.5 companion.

Gliese 806

Gliese 806 is a red dwarf star in the constellation of Cygnus, located roughly 41 light years from the Sun. The star is suspected to host a substellar companion yet unconfirmed.

Gordon J. Stanley

Gordon J. Stanley (1921–2001) was a New Zealand-born radio astronomer who with John G. Bolton in 1947 discovered the first radio star.

Stanley was born in Cambridge, New Zealand. By the 1940s he was working in radio astronomy with Bolton, where they discovered Cygnus A, the first radio star.

In 1955 Stanley went to the California Institute of Technology (Caltech) where he became the director of the Owen Valley Radio Observatory.

HD 185435

HD 185435 is a star in the constellation Cygnus. Its apparent magnitude is 6.42.

HD 189276

HD 189276 is a star in the constellation Cygnus. Its apparent magnitude is 4.96.

HD 197036

HD 197036 is a 7th magnitude star in the constellation Cygnus, approximately 2000 light years away from Earth. It is a bluish white subgiant star of the spectral type B5IV, meaning it possesses a surface temperature of 11,000 to 25,000 kelvins. It is therefore hotter, larger, and brighter than our Sun. It can be found within one degree of the star Deneb.

Kepler-17

Kepler-17 is a star around which the planet Kepler-17b orbits.

Kepler-28

Kepler-28 is a star in the northern constellation of Cygnus., It is orbited by two exoplanets. It is located at the celestial coordinates: Right Ascension 19h 28m 32.887s, Declination +42° 25′ 45.91″. With an apparent visual magnitude of 15.036, this star is too faint to be seen with the naked eye.

Kepler-42c

Kepler-42 c, previously KOI-961.02 then KOI-961 c, is an exoplanet orbiting Kepler-42, a star located about 131 light-years (40 pc) from the Solar System, in the constellation of Cygnus. A planetary system of at least three exoplanets with sizes between Mars and Venus has been detected around this red dwarf on January 11, 2012 by the method of transits with the help of the space telescope Kepler.

Kepler-42 c is a planet with a radius 0.73 times that of Earth. It orbits its star in a little less than 11 hours at about 0.006 AU of its host star and has an average equilibrium temperature of about 445°C (833°F). Due to the temperature, it is not suitable for life.

It is tidally locked in a synchronous rotation. Thus, it makes one complete rotation each time it completes an orbit. As a result, there is an eternal day side and a permanent night side.

Kepler-66

Kepler-66 is a star with slightly more mass than the Sun in the NGC 6811 open cluster in the Cygnus constellation. It has one confirmed planet, slightly smaller than Neptune, announced in 2013.

Kepler-67

Kepler-67 is a star with slightly less mass than the Sun in the NGC 6811 open cluster in the Cygnus constellation and has one confirmed planet, slightly smaller than Neptune, announced in 2013.

Mrinal Kumar Das Gupta

Mrinal Kumar Das Gupta (1 September 1923 – 28 November 2005, Kolkata) was an Indian astronomer. He was born in erstwhile Barishal district in present-day Bangladesh. He received his B.Sc and M.Sc degrees in Physics from Dhaka University in 1944 and 1945 respectively. Later he joined the department of Radio Physics and Electronics of the University of Calcutta as a researcher. In 1954, he obtained his Ph.D. from the University of Manchester. Later he became the head of the department of the Institute of Radio Physics and Electronics at Calcutta University. Das Gupta worked with Robert Hanbury Brown and Roger Jennison, in building the first intensity interferometers at radio wavelength in the early 1950s and measured the apparent angular structures of two radio sources, Cygnus A and Cassiopeia A. Das Gupta was elected as a Fellow of the National Academy of Science in 1974 by the Indian National Science Academy, New Delhi and as a Fellow of the Academy of Science by the Indian Academy of Sciences, Bangalore. He died on 28 November 2005 in Kolkata.

Polar-ring galaxy

A polar-ring galaxy is a type of galaxy in which an outer ring of gas and stars rotates over the poles of the galaxy. These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy. The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar-ring structure.The best-known polar-ring galaxies are S0s (lenticular galaxies), but from the physical point of view they are part of a wider category of galaxies, including several ellipticals.

The first four S0 galaxies that were identified as polar-ring galaxies were NGC 2685, NGC 4650A, A 0136 -0801, and ESO 415 -G26. While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified. Polar-ring S0 galaxies may be found around 0.5% of all nearby lenticular galaxies, and it is possible that 5% of lenticular galaxies may have had polar rings at some point during their lifetimes.The first polar-ring elliptical galaxies were identified in 1978. They were NGC 5128, NGC 5363, NGC 1947 and Cygnus A, while the polar-ring S0 galaxies NGC 2685 and NGC 4650A were at that time indicated as resulting from similar formation processes. Only some years later, when the first observations of the stellar and gas motion of polar-ring elliptical and S0 galaxies were possible with a better spectroscopic technology, the external origin of the gaseous rings was clarified. In addition to the best-known example, NGC 5128 (Cen A), a very regular polar ring elliptical, is NGC 5266

Roger Clifton Jennison

Roger Clifton Jennison (18 December 1922 – 29 December 2006) worked as a radio astronomer at Jodrell Bank under the guidance of Robert Hanbury Brown. Jennison made a number of discoveries in the field of radio astronomy, including the discovery of the double nature of radio source Cygnus A (3C 405.0) with M K Das Gupta and the mapping of Cassiopeia A with V Latham.

Sea interferometry

Sea interferometry, also known as Sea-cliff interferometry, is a form of radio astronomy that uses radio waves reflected off the sea to produce an interference pattern. It is the radio wave analogue to Lloyd's mirror. The technique was invented and exploited in Australia between 1945 and 1948.A radio detecting aerial is placed on top of a cliff, which detects electromagnetic waves coming directly from the source and waves reflected off the water surface. The two sets of waves are then combined to form an interference pattern such as that produced by two separate aerials. The reflected wavefront travels an additional distance 2h sin(i) before reaching the detector where h and i are the height of the cliff and the inclination of the incoming wavefront respectively. It acts as a second aerial twice the height of the cliff below the first.Sea interferometers are drift instruments, that is, they are fixed and their pointing direction changes with the rotation of the Earth.

The interference patterns for a sea interferometer commence sharply as soon as the source rises above the horizon, instead of fading in gradually as for a normal interferometer. Since it consists of just one detector, there is no need for connecting cables or for preamplifiers. A sea interferometer also has double the sensitivity of a pair of detectors set up to the same separation. Sea interferometry greatly increases the resolving power of the instrument.The quality of data obtained by a sea interferometer is affected by a number of factors. Waves on the water surface and variable refraction adversely affect the signal, and the curvature of the Earth's surface must be taken into account. These difficulties can be overcome by observing for extended periods, and calibrating the instrument on sources of known position.Among the discoveries made using sea interferometry are that sunspots emit strong radio waves

and that the source of radio wave emission from Cygnus A is small (less than 8 arcminutes in diameter). The technique also discovered six new sources including Centaurus A.

V1057 Cygni

V1057 Cygni (V1057 Cyg) is a FU Orionis-type variable star in the constellation of Cygnus. It has a spectral type of F and an apparent visual magnitude of approximately 11.660. It was the second FU Orionis-type variable discovered.

V1668 Cygni

V1668 Cygni was a nova that appeared in the constellation Cygnus in 1978 with a maximum brightness of 6th apparent magnitude.

V476 Cygni

V476 Cygni or Nova Cygni 1920 was a nova which occurred in the constellation Cygnus in 1920. It reached a brightness of 2.0 mag. Nowadays its brightness is 17.09 mag.

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