Tuesday, November 10, 2009

The “Cassiopeia A” Puzzle May Be Solved

Supernova remnant Cassiopeia A is one of the youngest in the Milky Way Galaxy, located about 3.4 kiloparsecs (11,000 light-years) away. The expanding cloud of material is now about 10 light-years across. The cloud is very faint optically, only visible in long-exposure photographs. However, it is a very bright radio source.

The supernova remnant was officially discovered in 1947 by radio astronomers from Cambridge, England. It was first named Cassiopeia A and later cataloged as 3C 461. The radio source was not visually confirmed until 1950.

The age of the supernova is not certain. Based on the cloud’s angular expansion rate, astronomers calculate that the expansion began around AD 1667. Interestingly enough, it is possible that the supernova may have been observed on August 16, 1680, by British astronomer John Flamsteed (1646-1719) when he recorded what he described as a sixth magnitude star “3 Cassiopeiae.” Some suggest this may have been shortly after the supernova event, because the expanding cloud of material would have been very bright immediately following the supernova event.

The fate of the star which became a supernova remnant has long been a puzzle to astronomers. They thought it might have become a black hole or a neutron star, but did not known for certain.

Astronomers could not see the core of the remnant until 1999, when NASA’s Chandra X-Ray Observatory first imaged the collapsed star. But even with this new information, astronomers are still questioning. The amount of energy it radiates was either much too small for a neutron star, and there were no pulses observed in the radiation and it had a low magnetic field (so not a pulsar/neutron star). The astronomers found a carbon atmosphere, which was also puzzling. The recent thought is that the hydrogen and helium from the remnant were falling back onto the star’s very hot surface (with temperatures up to 1 billion Kelvin, or 2 billion degrees Fahrenheit), allowing it to perform fusion on these and change them into carbon.

The latest studies suggest that this is what a neutron star looks like when it is very, very young. As it gets older, it will cool quite a bit, eventually stop burning the hydrogen and helium into carbon, and develop a hydrogen atmosphere. To learn more, check out this link:

NASA’s Chandra X-Ray Observatory
http://www.nasa.gov/mission_pages/chandra/main/index.html

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