|
X-rays provide a new way to investigate exploding stars
May 10, 2007ESA's X-ray observatory XMM-Newton has revealed a new class of exploding stars - where the X-ray emission 'lives fast and dies young'.
The identification of this particular class of explosions gives astronomers a valuable new constraint to help them model and understand stellar explosions.
Exploding stars called novae remain a puzzle to astronomers. "Modelling these outbursts is very difficult," says Wolfgang Pietsch of the Max Planck Institut für Extraterrestrische Physik. 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.
Between July 2004 and February 2005, the X-ray observatories watched the heart of the nearby galaxy, Andromeda, also known to astronomers as M31. During that time, Pietsch and his colleagues monitored novae, looking for the X-rays.
They detected that eleven out 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," says Pietsch.
White dwarfs are hot stellar corpses left behind after the rest of the star has been ejected into space. A typical white dwarf contains about the mass of the Sun, in a spherical volume little bigger than the Earth. Given its density, it has a strong pull of gravity. If in orbit around a normal star, it may rip gas from the star.
This material builds up on the surface of the white dwarf until it reaches sufficient density for a nuclear detonation. The resultant explosion creates a nova visible in the optical region for a few to a hundred days. However, these particular events are not strong enough to destroy the underlying white dwarf.
The X-ray emission becomes visible some time after the detonation, when the matter ejected by the nova thins out. This allows astronomers to peer down to the atmosphere of the white dwarf, which is burning by nuclear fusion.
At the end of the process, the X-ray emission stops when the fuel is exhausted. The duration of this X-ray emission traces the amount of material left on the white dwarf after the nova has ended.
A well determined start time of the optical nova outburst and the X-ray turn-on and turn-off times are therefore important benchmarks, or constraints, 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," says Pietsch. 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.
In addition to discovering the short-lived ones, the new survey also confirms that other novae generate 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.
The differing lengths of times are thought to reflect the masses of the white dwarfs at the heart of the nova explosion. The fastest evolving novae are thought to be those coming from the most massive white dwarfs.
To investigate further, the team, lead by Dr. Pietsch, have been awarded more XMM-Newton and Chandra observing time. They now plan to monitor M31's novae every ten days for several months, starting in November 2007, to glean more information about these puzzling stellar explosions.
European Space Agency
They detected that eleven out 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," says Pietsch.
White dwarfs are hot stellar corpses left behind after the rest of the star has been ejected into space. A typical white dwarf contains about the mass of the Sun, in a spherical volume little bigger than the Earth. Given its density, it has a strong pull of gravity. If in orbit around a normal star, it may rip gas from the star.
This material builds up on the surface of the white dwarf until it reaches sufficient density for a nuclear detonation. The resultant explosion creates a nova visible in the optical region for a few to a hundred days. However, these particular events are not strong enough to destroy the underlying white dwarf.
The X-ray emission becomes visible some time after the detonation, when the matter ejected by the nova thins out. This allows astronomers to peer down to the atmosphere of the white dwarf, which is burning by nuclear fusion.
At the end of the process, the X-ray emission stops when the fuel is exhausted. The duration of this X-ray emission traces the amount of material left on the white dwarf after the nova has ended.
A well determined start time of the optical nova outburst and the X-ray turn-on and turn-off times are therefore important benchmarks, or constraints, 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," says Pietsch. 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.
In addition to discovering the short-lived ones, the new survey also confirms that other novae generate 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.
The differing lengths of times are thought to reflect the masses of the white dwarfs at the heart of the nova explosion. The fastest evolving novae are thought to be those coming from the most massive white dwarfs.
To investigate further, the team, lead by Dr. Pietsch, have been awarded more XMM-Newton and Chandra observing time. They now plan to monitor M31's novae every ten days for several months, starting in November 2007, to glean more information about these puzzling stellar explosions.
European Space Agency
Xmm-newton News and Current Xmm-newton Events RSSCommon star draws swift attention with unprecedented flare
On April 25, one of our nearest stellar neighbors, a small, faint red dwarf known as EV Lacertae, unleashed the brightest flare ever detected from a normal star outside our solar system.
Milky Way's Giant Black Hole Awoke from Slumber 300 Years Ago
Using NASA, Japanese, and European X-ray satellites, a team of Japanese astronomers has discovered that our galaxy's central black hole let loose a powerful flare three centuries ago.
Cosmic engines surprise XMM-Newton
XMM-Newton has been surprised by a rare type of galaxy, from which it has detected a higher number of X-rays than thought possible. The observation gives new insight into the powerful processes shaping galaxies during their formation and evolution.
Action Replay of Powerful Stellar Explosion
Astronomers have made the best ever determination of the power of a supernova explosion that was visible from Earth long ago. By observing the remnant of a supernova and a light echo from the initial outburst, they have established the validity of a powerful new method for studying supernovas.
Supernova remnants dance in the LMC
The Gemini South Multi-Object Spectograph (GMOS) recently captured a dramatic image of a vast cloud complex named DEM L316 located in the Large Magellanic Cloud.
Neutron stars warp space-time, U-M astronomers observe
Einstein's predicted distortion of space-time occurs around neutron stars, University of Michigan astronomers and others have observed.
Astronomers Pioneer New Method For Probing Exotic Matter
Using European and Japanese/NASA X-ray satellites, astronomers have seen Einstein's predicted distortion of space-time around three neutron stars, and in doing so they have pioneered a groundbreaking technique for determining the properties of these ultradense objects.
XMM-Newton and Suzaku help pioneer method for probing exotic matter
Astronomers using XMM-Newton and Suzaku have seen Einstein's predicted distortion of space-time and pioneered a ground-breaking technique for determining the properties of neutron stars.
X-ray satellites discover the biggest collisions in the Universe
The orbiting X-ray telescopes XXM-Newton and Chandra have caught a pair of galaxy clusters merging into a giant cluster. The discovery adds to existing evidence that galaxy clusters can collide faster than previously thought.
XMM-Newton reveals X-rays from gas streams around young stars
XMM-Newton has surveyed nearly two hundred stars under formation to reveal, contrary to expectations, how streams of matter fall onto the young stars' magnetic atmospheres and radiate X-rays.
More Xmm-newton News Articles
| Iron Features in the XMM-Newton Sprectrum of NGC 4151 by N. J.; Warwick, R. S.; Griffiths, R. E. Ptak, A. F. Schurch |
| © 2008 BrightSurf.com |