Changes

{{Night Sky

{{Night Sky

| image          =

| image          =Cassiopeia A Spitzer Crop.jpg

| designation    =Cas A

| designation    =Cas A

| rightascension  =23^h 23^m 26^s<ref name=constellation-guide>[http://www.constellation-guide.com/cassiopeia-a/ Cassiopeia A] from constellation-guide.com</ref>

| rightascension  =23^h 23^m 26^s<ref name=constellation-guide>[http://www.constellation-guide.com/cassiopeia-a/ Cassiopeia A] from constellation-guide.com</ref>

At around 11,000 [[light year]]s away, the nebula's apparent size of 5 arcminutes corresponds to a physical diameter of around 10 light years.<ref name=constellation-guide/> 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.<ref name=constellation-guide/> 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 around 11,000 [[light year]]s away, the nebula's apparent size of 5 arcminutes corresponds to a physical diameter of around 10 light years.<ref name=constellation-guide/> 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.<ref name=constellation-guide/> 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]].<ref name=britannica>[https://www.britannica.com/place/Cassiopeia-A Cassiopeia A] from britannica.com</ref> The star is also cooling very quickly, decreasing by 4% over the ten years it has been observed by the [[Chandra Space Telescope]].<ref>[http://chandra.harvard.edu/photo/2011/casa/ Cassiopeia A: NASA'S Chandra Finds Superfluid in Neutron Star's Core] from chandra.harvard.edu</ref> 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]].<ref name=constellation-guide/>

At the centre of the nebula is a [[neutron star]]. It was the first neutron star to observed to possess an atmosphere containing [[carbon]].<ref name=britannica>[https://www.britannica.com/place/Cassiopeia-A Cassiopeia A] from britannica.com</ref> The star is also cooling very quickly, decreasing by 4% over the ten years it has been observed by the [[Chandra|Chandra Space Telescope]].<ref>[http://chandra.harvard.edu/photo/2011/casa/ Cassiopeia A: NASA'S Chandra Finds Superfluid in Neutron Star's Core] from chandra.harvard.edu</ref> 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]].<ref name=constellation-guide/>

The nebula is a very bright [[radio waves|radio]] source, the most luminous visible from [[Earth]] for [[frequency|frequencies]] above 1 GHz. Below this , the radio source [[Cygnus A]] is brighter.

The nebula is a very bright [[radio waves|radio]] source, the most luminous visible from [[Earth]] for [[frequency|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.<ref name=constellation-guide/><ref>[https://www.nasa.gov/mission_pages/chandra/multimedia/exploring-cassiopeiaA.html Exploring the Third Dimension of Cassiopeia A] from nasa.gov</ref> This model was generated using data from [[NASA]]'s Chandra Space Telescope and its [[Spitzer Space Telescope]]. 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.<ref name=constellation-guide/>

The nebula has been modelled in 3D and is the only supernova remnant for which this has been done.<ref name=constellation-guide/><ref>[https://www.nasa.gov/mission_pages/chandra/multimedia/exploring-cassiopeiaA.html Exploring the Third Dimension of Cassiopeia A] from nasa.gov</ref> 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 Space Telescope|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.<ref name=constellation-guide/>

==References==

==References==