Кассиопея А: Галактикалық супернова қалдығы

Supernova remnant in the constellation Cassiopeia

Cassiopeia A (Cas A) 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 away within the Milky Way; 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 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. 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. The optical component was first identified in 1950. 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. 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. 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. 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. 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. 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. Cas XR 1 was discovered by an Aerobee rocket flight on 25 April 1965, at RA Dec Cas X 1 is Cas A, a Type II SNR at RA Dec 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, a central compact object that is the neutron star remnant left by the explosion.

In 2005 an infrared echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope. 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. 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. In 2011 a study used spectra from different positions of the light echo to confirm that the Cassiopeia A supernova was asymmetric.

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.