Cassiopeia A
| Cassiopeia A | |
|---|---|
| |
| Observational Data | |
| Designation | Cas A |
| Right ascension | 23h 23m 26s[1] |
| Declination | +58° 48′[1] |
| Constellation | Cassiopeia |
| Type of object | Supernova remnant |
| Dimensions | 3 arcminutes[1] |
| Astrometry | |
| Distance from Earth | 11,000 ly[1] |
Cassiopeia A (Cas A) is a supernova remnant in the constellation of Cassiopeia.[1] The supernova that caused it is thought to have occurred around 300 years ago, though no definite recording of a supernova was made at that time. One possibility of it may have been made by John Flamsteed on August 16, 1680. Flamsteed observed a star with an apparent magnitude of +6 near the nebula but Flamsteed's position for the star does not correspond to any known star today.[1] The nebula also houses a radio source, designated Cas A and first observed in 1947.[1] For frequencies above 1 GHz, Cassiopeia A is the brightest radio source in the night sky.
Properties and Structure
At around 11,000 light years away, the nebula's apparent size of 5 arcminutes corresponds to a physical diameter of around 10 light years.[1] The nebula's outer shell is expanding at roughly 4,000-6,000 km/s and is believed to have a temperature of 27.7 million Kelvin.[1] The expansion rate suggests it cannot be more than a couple of hundred years old, though no record of a supernova exists at that time. This may be because the star ejected most of its outer layers or perhaps it was hidden behind a cloud of interstellar gas and dust.
At the centre of the nebula is a neutron star. It was the first neutron star to observed to possess an atmosphere containing carbon.[2] The star is also cooling very quickly, decreasing by 4% over the ten years it has been observed by the Chandra Space Telescope.[3] It is believed this indicates the core of the star is a superfluid. In 2013 the element phosphorus was also detected in the nebula as a whole in concentrations more than 100 times greater than the average for the Milky Way.[1]
The nebula is a very bright radio source, the most luminous visible from Earth for frequencies above 1 GHz. Below this, the radio source Cygnus A is brighter.
The nebula has been modelled in 3D and is the only supernova remnant for which this has been done.[1][4] This model was generated using data from NASA's Chandra Space Telescope and its Spitzer Space Telescope. The image on the right is a false colour image generated from the observations of Spitzer (in infrared light) and Hubble (in visible light). From this it was discovered that there are perhaps 6 or so empty chambers within the nebula. These are large, two of them being 3 and 6 light years across.[1]
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Cassiopeia A from constellation-guide.com
- ↑ Cassiopeia A from britannica.com
- ↑ Cassiopeia A: NASA'S Chandra Finds Superfluid in Neutron Star's Core from chandra.harvard.edu
- ↑ Exploring the Third Dimension of Cassiopeia A from nasa.gov
