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Cassiopeia A

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Cassiopeia A
A false color image composed of data from three sources: Red is infrared data from the Spitzer Space Telescope, gold is visible data from the Hubble Space Telescope, and blue and green are data from the Chandra X-ray Observatory. The small, bright, baby-blue dot just off-center is the remnant of the star's core.
Event typeSupernova remnant, astronomical radio source Edit this on Wikidata
ConstellationCassiopeia Edit this on Wikidata
Right ascension23h 23m 24s
Declination+58° 48.9
Galactic coordinates111.734745°, −02.129570°
Distance11,000 ly (3.4 kpc)[2]
HostMilky Way
Progenitor typeunknown
Colour (B-V)unknown
Notable featuresStrongest radio source beyond our solar system
Peak apparent magnitude6?
Other designationsSN 1671, SN 1667, SN 1680, SNR G111.7-02.1, 1ES 2321+58.5, 3C 461, 3C 461.0, 4C 58.40, 8C 2321+585, 1RXS J232325.4+584838, 3FHL J2323.4+5848, 2U 2321+58, 3A 2321+585, 3CR 461, 3U 2321+58, 4U 2321+58, AJG 109, CTB 110, INTREF 1108, [DGW65] 148, PBC J2323.3+5849, 2FGL J2323.4+5849, 3FGL J2323.4+5849, 2FHL J2323.4+5848
Preceded bySN 1604
Followed byG1.9+0.3 (unobserved, c. 1868), SN 1885A (next observed)
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Cassiopeia A (Cas A) (listen) is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way;[2][3] given the width of the Orion Arm, it lies in the next-nearest arm outwards, the Perseus Arm, about 30 degrees from the Galactic anticenter. The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. It has been seen in wavelengths of visible light with amateur telescopes down to 234 mm (9.25 in) with filters.[4]

It is estimated that light from the supernova itself first reached Earth near the 1690s, although there are no definitively corresponding records from then. Cas A is circumpolar at and above mid-Northern latitudes which had extensive records and basic telescopes. Its likely omission in records is probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth, although it is possible that it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed. Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and absorbed much of the visible-light emission as the inner star collapsed.

Cas A was among the first discrete astronomical radio sources found. Its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer.[5] The optical component was first identified in 1950.[6]

Possible observations[edit]

Calculations working back from the currently observed expansion point to an explosion that would have become visible on Earth around 1667. Astronomer William Ashworth and others have suggested that the Astronomer Royal John Flamsteed may have inadvertently observed the supernova on 16 August [O.S. 6 August] 1680, when he catalogued a sixth-magnitude star 3 Cassiopeiae, but there is no corresponding star at the recorded position. Possible explanations include an error in the position,[7] or that a transient was recorded. Caroline Herschel noted that a star in the vicinity of τ Cas, HD 220562, fit well with 3 Cas if a common error in sextant readings was made.[8] Alternatively, the star AR Cassiopeiae may have been observed, again with the position recorded incorrectly. The position and timing mean that it may have been an observation of the Cassiopeia A progenitor supernova.[9] Another suggestion from recent cross-disciplinary research is that the supernova was the "noon day star", observed in 1630, that was thought to have heralded the birth of Charles II, the future monarch of Great Britain.[10]

No supernova occurring within the Milky Way has been visible to the naked eye from Earth since.


The expansion shell has a temperature of around 30 million K, and is expanding at 4000−6000 km/s.[2]

Observations of the exploded star through the Hubble Space Telescope have shown that, despite the original belief that the remnants were expanding in a uniform manner, there are high velocity outlying eject knots moving with transverse velocities of 5,500−14,500 km/s with the highest speeds occurring in two nearly opposing jets.[2] When the view of the expanding star uses colors to differentiate materials of different chemical compositions, it shows that similar materials often remain gathered together in the remnants of the explosion.[3]

Radio source[edit]

Cas A had a flux density of 2720 ± 50 Jy at 1 GHz in 1980.[11] Because the supernova remnant is cooling, its flux density is decreasing. At 1 GHz, its flux density is decreasing at a rate of 0.97 ± 0.04 percent per year.[11] This decrease means that, at frequencies below 1 GHz, Cas A is now less intense than Cygnus A. Cas A is still the brightest extrasolar radio source in the sky at frequencies above 1 GHz.

X-ray source[edit]

Although Cas X-1 (or Cas XR-1), the apparent first X-ray source in the constellation Cassiopeia was not detected during the 16 June 1964, Aerobee sounding rocket flight, it was considered as a possible source.[12] Cas A was scanned during another Aerobee rocket flight of 1 October 1964, but no significant X-ray flux above background was associated with the position.[13] Cas XR-1 was discovered by an Aerobee rocket flight on 25 April 1965,[14] at RA 23h 21m Dec +58° 30′.[15] Cas X-1 is Cas A, a Type II SNR at RA 23h 18m Dec +58° 30′.[16] The designations Cassiopeia X-1, Cas XR-1, Cas X-1 are no longer used, but the X-ray source is Cas A (SNR G111.7-02.1) at 2U 2321+58.

In 1999, the Chandra X-Ray Observatory found CXOU J232327.8+584842,[17] a central compact object that is the neutron star remnant left by the explosion.[18]

Supernova reflected echo[edit]

In 2005 an infrared echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope.[19] The infrared echo was also seen by IRAS and studied with the Infrared Spectrograph. Previously it was suspected that a flare in 1950 from a central pulsar could be responsible for the infrared echo. With the new data it was concluded that this is unlikely the case and that the infrared echo was caused by thermal emission by dust, which was heated by the radiative output of the supernova during the shock breakout.[20] The infrared echo is accompanied by a scattered light echo. The recorded spectrum of the optical light echo proved the supernova was of Type IIb, meaning it resulted from the internal collapse and violent explosion of a massive star, most probably a red supergiant with a helium core which had lost almost all of its hydrogen envelope. This was the first observation of the light echo of a supernova whose explosion had not been directly observed which opens up the possibility of studying and reconstructing past astronomical events.[1][6] In 2011 a study used spectra from different positions of the light echo to confirm that the Cassiopeia A supernova was asymmetric.[21]

Phosphorus detection[edit]

In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae through supernova nucleosynthesis. The phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the Milky Way in general.[22]


See also[edit]


  1. ^ a b Krause, Oliver; Birkmann; Usuda; et al. (2008). "The Cassiopeia A supernova was of Type IIb". Science. 320 (5880): 1195–1197. arXiv:0805.4557. Bibcode:2008Sci...320.1195K. doi:10.1126/science.1155788. PMID 18511684. S2CID 40884513.
  2. ^ a b c d Fesen, Robert A.; Hammell, Molly C.; Morse, Jon; Chevalier, Roger A.; Borkowski, Kazimierz J.; Dopita, Michael A.; Gerardy, Christopher L.; Lawrence, Stephen S.; Raymond, John C.; van den Bergh, Sidney (July 2006). "The expansion asymmetry and age of the Cassiopeia A supernova remnant". The Astrophysical Journal. 645 (1): 283–292. arXiv:astro-ph/0603371. Bibcode:2006ApJ...645..283F. doi:10.1086/504254. S2CID 8999768.
  3. ^ a b Stover, Dawn (2006). "Life in a bubble". Popular Science. Vol. 269, no. 6. p. 16.
  4. ^ Banich, Howard (December 2014). "A visual guide to the Cassiopeia A supernova remnant". Sky & Telescope.
  5. ^ Ryle, M.; Smith, F. G. (18 September 1948). "A new intense source of radio-frequency radiation in the constellation of Cassiopeia". Nature. 162 (4116): 462–463. Bibcode:1948Natur.162..462R. doi:10.1038/162462a0. S2CID 4028114.
  6. ^ a b Fabian, Andrew C. (2008). "A blast from the past". Astronomy. Science. 320 (5880): 1167–1168. doi:10.1126/science.1158538. PMID 18511676. S2CID 206513073.
  7. ^ Ashworth, W. B. (1980). "A Probable Flamsteed Observation of the Cassiopeia a Supernova". Journal for the History of Astronomy. 11: 1. Bibcode:1980JHA....11....1A. doi:10.1177/002182868001100102. S2CID 121684168.
  8. ^ Ashworth, William B. (February 1980). "A Probable Flamsteed Observation of the Cassiopeia a Supernova". Journal for the History of Astronomy. 11 (1): 1–9. Bibcode:1980JHA....11....1A. doi:10.1177/002182868001100102. ISSN 0021-8286. S2CID 121684168.
  9. ^ Hughes, D.W. (1980). "Did Flamsteed see the Cassiopeia A supernova?". Nature. 285 (5761): 132–133. Bibcode:1980Natur.285..132H. doi:10.1038/285132a0. S2CID 4257241.
  10. ^ Oullette, Jennifer. "Did supernova herald the birth of a king?". Discovery.com. Archived from the original on 29 September 2012. Retrieved 18 April 2011.
  11. ^ a b Baars, J.W.M.; Genzel, R.; Pauliny-Toth, I.I.K.; Witzel, A. (1977). "The absolute spectrum of Cas A; an accurate flux density scale and a set of secondary calibrators". Astronomy and Astrophysics. 61: 99. Bibcode:1977A&A....61...99B.
  12. ^ Bowyer S, Byram ET, Chubb TA, Friedman H (1965). "Observational results of X-ray astronomy". In Steinberg JL (ed.). Astronomical Observations from Space Vehicles, Proceedings from Symposium No. 23 Held in Liege, Belgium, 17 to 20 August 1964. Astronomical Observations from Space Vehicles. Vol. 23. International Astronomical Union. pp. 227–239. Bibcode:1965IAUS...23..227B.
  13. ^ Fisher PC, Johnson HM, Jordan WC, Meyerott AJ, Acton LW (1966). "Observations of cosmic X-rays". Astrophysical Journal. 143: 203–17. Bibcode:1966ApJ...143..203F. doi:10.1086/148491.
  14. ^ Byram ET, Chubb TA, Friedman H (Apr 1966). "Cosmic X-ray sources, galactic and extragalactic". Science. 152 (3718): 66–71. Bibcode:1966Sci...152...66B. doi:10.1126/science.152.3718.66. PMID 17830233. S2CID 122616358.
  15. ^ Friedman H, Byram ET, Chubb TA (April 1967). "Distribution and variability of cosmic X-ray sources". Science. 156 (3773): 374–8. Bibcode:1967Sci...156..374F. doi:10.1126/science.156.3773.374. PMID 17812381. S2CID 29701462.
  16. ^ Webber, W.R. (December 1968). "X-ray astronomy-1968 vintage". Proceedings of the Astronomical Society of Australia. 1 (4): 160–164. Bibcode:1968PASA....1..160W. doi:10.1017/S1323358000011231. S2CID 119018154.
  17. ^ "CXOU J232327.8+584842". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-03-03.
  18. ^ Elshamouty, K.G.; Heinke, C.O.; Sivakoff, G.R.; Ho, W.C.G.; Shternin, P.S.; Yakovlev, D.G.; Patnaude, D.J.; David, L. (2013). "Measuring the cooling of the neutron star in Cassiopeia A with all Chandra X-Ray Observatory detectors". Astrophysical Journal. 777 (1): 22. arXiv:1306.3387. Bibcode:2013ApJ...777...22E. doi:10.1088/0004-637X/777/1/22. S2CID 17981919.
  19. ^ Krause, Oliver; Rieke, George H.; Birkmann, Stephan M.; Le Floc'h, Emeric; Gordon, Karl D.; Egami, Eiichi; Bieging, John; Hughes, John P.; Young, Erick T.; Hinz, Joannah L.; Quanz, Sascha P. (June 2005). "Infrared Echoes near the Supernova Remnant Cassiopeia A". Science. 308 (5728): 1604–1606. arXiv:astro-ph/0506186. Bibcode:2005Sci...308.1604K. doi:10.1126/science.1112035. ISSN 0036-8075. PMID 15947181. S2CID 21908980.
  20. ^ Dwek, Eli; Arendt, Richard G. (October 2008). "Infrared Echoes Reveal the Shock Breakout of the Cas A Supernova". Astrophysical Journal. 685 (2): 976–987. arXiv:0802.0221. Bibcode:2008ApJ...685..976D. doi:10.1086/589988. ISSN 0004-637X.
  21. ^ Rest, A.; Foley, R. J.; Sinnott, B.; Welch, D. L.; Badenes, C.; Filippenko, A. V.; Bergmann, M.; Bhatti, W. A.; Blondin, S.; Challis, P.; Damke, G. (May 2011). "Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes". Astrophysical Journal. 732 (1): 3. arXiv:1003.5660. Bibcode:2011ApJ...732....3R. doi:10.1088/0004-637X/732/1/3. ISSN 0004-637X. S2CID 119266059.
  22. ^ Koo, B.-C.; Lee, Y.-H.; Moon, D.-S.; Yoon, S.-C.; Raymond, J.C. (2013). "Phosphorus in the young supernova remnant Cassiopeia A". Science. 342 (6164): 1346–1348. arXiv:1312.3807. Bibcode:2013Sci...342.1346K. doi:10.1126/science.1243823. PMID 24337291. S2CID 35593706.

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