Cassiopeia A

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
IIb[1]
Date1947 by Martin Ryle and Francis Graham-Smith)
ConstellationCassiopeia
Right ascension23h 23m 24s
Declination+58° 48.9′
EpochJ2000
Galactic coordinates111.734745°, −02.129570°
Distancec. 11,000 ly[2]
RemnantShell
HostMilky Way
Notable featuresStrongest radio source beyond our solar system
Peak apparent magnitudec. 6
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]

  1. ^ Cite error: The named reference Krause was invoked but never defined (see the help page).
  2. ^ a b 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. ^ 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. ^ Cite error: The named reference Fabian2008 was invoked but never defined (see the help page).