ESAs Newton X-ray reveals new class of stellar explosions

The European Space Agencys (ESAs) XMM-Newton X-ray has identified a new class of stellar explosions - where the X-ray emissions live fast and die young.

Paris, May 10 : The European Space Agency's (ESA's) XMM-Newton X-ray has identified a new class of stellar explosions - where the X-ray emissions 'live fast and die young'.

Exploding stars called novae have remained an enigma for astronomers. As such, the identification of this particular class of explosions would give astronomers a valuable new constraint to help them model and understand stellar explosions.

"Modelling these outbursts is very difficult. Now, ESA's XMM-Newton and NASA's Chandra space-borne X-ray observatories have provided valuable information about when individual novae emit X-rays," said Wolfgang Pietsch of the Max Planck Institut f�r Extraterrestrische Physik.

Between July 2004 and February 2005, the X-ray observatories watched the heart of the nearby galaxy, Andromeda, also known as M31.

During that time, Pietsch and his colleagues monitored novae, looking for the X-rays.

The team detected that 11 of the 34 novae that had exploded in the galaxy during the previous year were shining X-rays into space.

"X-rays are an important window onto novae. They show the atmosphere of the white dwarf," said Pietsch.

He said, as the duration of the X-ray emission traced the amount of material left on the white dwarf after the nova had ended, a well-determined start time of the optical nova outburst and the X-ray turn-on and turn-off times were important benchmarks for replication in computer models of novae.

Whilst monitoring the M31 novae frequently over several months for the appearance and subsequent disappearance of the X-rays, Pietsch made an important discovery; some novae started to emit X-rays and then turned them off again within just a few months.

"These novae are a new class. They would have been overlooked before. That's because previous surveys looked only every six months or so. Within that time, the fast X-ray novae could have blinked both on and off," said Pietsch.

In addition to discovering the short-lived ones, the researchers also confirmed that other novae generated X-rays over a much longer time. XMM-Newton detected seven novae that were still shining X-rays into space, up to a decade after the original eruption. esearchers believe the differing lengths of times reflect the masses of the white dwarfs at the heart of the nova explosion.

According to them, the fastest evolving novae are thought to be those coming from the most massive white dwarfs.

The findings appear in the paper "X-ray monitoring of optical novae in M31 from July 2004 to February 2005", published in the April 2007 issue of the journal Astronomy and Astrophysics.

ANI