Canadian physicist IDs young neutron star

A physicist from the University of Alberta is part of a team that has identified an unusual neutron star left over from a supernova first seen 330 years ago.

Craig Heinke and his colleague Wynn Ho at the University of Southampton, U.K., say that the remnant of the supernova Cassiopeia A is a very young neutron star, 20 times heavier than the sun, but only 20 kilometres wide.

The star, about 11,000 light-years away, is unusual because it has a thin atmosphere of carbon, about 10 centimetres thick.

While the supernova that created Cassiopeia A is thought to have been seen in 1680 by Britain's first Astronomer Royal, John Flamsteed, the compact X-ray source at the centre of the remnant wasn't discovered until 1999.

Astronomers examining the X-ray radiation from the supernova remnant were puzzled by its spectrum. According to their models of how stars evolve, the X-ray spectrum suggested the remnant was either very small, possibly a black hole, or was a neutron star with hot polar caps, which was difficult to explain.

Ho and Heinke, in this week's issue of the journal Nature, show that the spectrum recorded by the Chandra X-ray Observatory satellite could be explained by a normal-sized neutron star with a carbon atmosphere and a low magnetic field.

"This neutron star was born so hot that nuclear fusion happened on its surface, producing a carbon atmosphere just 10 centimetres thick," said Heinke in a statement.

Heinke describes Cassiopeia A as a neutron star in its infancy, which hasn't yet cooled enough to accumulate an atmosphere of hydrogen and helium, as seen in older neutron stars.

"This discovery helps us understand how neutron stars are born in violent supernova explosions," said Heinke.

The identification of the remnant as a young neutron star also gives scientists a more complete picture of the life cycle of a supernova.