Andrew Yee[_1_]
June 9th 08, 06:20 PM
ESA News
http://www.esa.int
5 June 2008
Integral reveals exotic and dusty binary systems
ESA's orbiting gamma-ray observatory, Integral has revealed a new population
of exotic and dusty binary stars which might represent a brief evolutionary
period in a binary star's life. The findings bring to light a gap in our
knowledge of the formation and evolution of such binary star systems.
Since 2002, when Integral was launched, the observatory has been surveying
the galaxy, looking for sources of the most powerful X-rays and gamma rays.
Fifteen of its new discoveries appeared to be so-called supergiant high-mass
X-ray binaries (HMXB). These binary systems consist of a neutron star
orbiting around a supergiant star. Before Integral, only seven supergiant
HMXBs were known.
The supergiant star is at least 20 times larger than the Sun, contains 30
solar masses, with luminosity one million times greater and a temperature of
20 000 K. The neutron star was once a massive star itself, but has reached
the end of its life and collapsed into a tiny stellar remnant just 15 km
across.
Sylvain Chaty, University of Paris Diderot and CEA Saclay France, and
colleagues have used Integral along with X-ray satellites and telescopes of
the European Southern Observatory (ESO) to target the 15 new discoveries and
confirm that most are indeed supergiant HMXBs, some of them enshrouded by a
cocoon of gas and dust.
"They are so deeply embedded that only Integral has the sensitivity to see
them," says Chaty. In each case, the neutron star is orbiting within the
outer atmosphere of its supergiant companion.
This may be a precursor of what astronomers refer to as the common envelope
phase, a short-lived period of a binary star's existence that is thought to
last for just a few thousand years. If so, it gives astronomers an
unprecedented opportunity to study this aspect of stellar evolution. It also
presents a problem.
These celestial pairings must once have been two supergiant stars in orbit
around one another. According to our computer models of how stars form and
evolve, such a supergiant pairing should be more scarce than Integral is
showing it to be.
"There must be many more of them than we thought you could have," says
Chaty, "So we don't quite know what is going on, yet."
High-mass X-ray binary stars offer a snapshot of star formation, but delayed
by about 10 million years. This is because the neutron star forms about 10
million years after the original system is formed, when the more massive of
the two stars has lived its life and collapsed.
Eventually, such a system will evolve further with the death of the
remaining supergiant star. At this point, a neutron star pair, or even a
neutron star-black hole pair, is formed. As these tiny stellar remnants
orbit one another, calculations show that they should lose energy and spiral
together. At the point of collision they may release a giant Gamma Ray
Burst.
A potential future ESA mission, currently undergoing technological
development, hopes to detect nearby neutron star pairs. Laser Interferometer
Space Antenna (LISA) will find them by spotting the gravitational waves they
radiate as they spiral together.
In the meantime, Integral has plenty of work to look for more supergiant
HMXBs and study the known ones further.
Notes for editors:
The following papers have been published today in the online issue of
Astronomy & Astrophyiscs:
'Multi-wavelength observations of Galactic hard X-ray sources discovered by
Integral.'
I. The nature of the companion star by S. Chaty, F. Rahoui, C. Foellmi, J.A.
Tomsick, J. Rodriguez, Walter
II. The environment of the companion star by F. Rahoui, S. Chaty, P.-O.
Lagage, E. Pantin
For more information:
Sylvain Chaty, University of Paris Diderot, France
Email: Chaty @ cea.fr
Christoph Winkler, ESA Integral Project Scientist
Email: Christoph.Winkler @ esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMSWO1YUFF_index_1.html ]
http://www.esa.int
5 June 2008
Integral reveals exotic and dusty binary systems
ESA's orbiting gamma-ray observatory, Integral has revealed a new population
of exotic and dusty binary stars which might represent a brief evolutionary
period in a binary star's life. The findings bring to light a gap in our
knowledge of the formation and evolution of such binary star systems.
Since 2002, when Integral was launched, the observatory has been surveying
the galaxy, looking for sources of the most powerful X-rays and gamma rays.
Fifteen of its new discoveries appeared to be so-called supergiant high-mass
X-ray binaries (HMXB). These binary systems consist of a neutron star
orbiting around a supergiant star. Before Integral, only seven supergiant
HMXBs were known.
The supergiant star is at least 20 times larger than the Sun, contains 30
solar masses, with luminosity one million times greater and a temperature of
20 000 K. The neutron star was once a massive star itself, but has reached
the end of its life and collapsed into a tiny stellar remnant just 15 km
across.
Sylvain Chaty, University of Paris Diderot and CEA Saclay France, and
colleagues have used Integral along with X-ray satellites and telescopes of
the European Southern Observatory (ESO) to target the 15 new discoveries and
confirm that most are indeed supergiant HMXBs, some of them enshrouded by a
cocoon of gas and dust.
"They are so deeply embedded that only Integral has the sensitivity to see
them," says Chaty. In each case, the neutron star is orbiting within the
outer atmosphere of its supergiant companion.
This may be a precursor of what astronomers refer to as the common envelope
phase, a short-lived period of a binary star's existence that is thought to
last for just a few thousand years. If so, it gives astronomers an
unprecedented opportunity to study this aspect of stellar evolution. It also
presents a problem.
These celestial pairings must once have been two supergiant stars in orbit
around one another. According to our computer models of how stars form and
evolve, such a supergiant pairing should be more scarce than Integral is
showing it to be.
"There must be many more of them than we thought you could have," says
Chaty, "So we don't quite know what is going on, yet."
High-mass X-ray binary stars offer a snapshot of star formation, but delayed
by about 10 million years. This is because the neutron star forms about 10
million years after the original system is formed, when the more massive of
the two stars has lived its life and collapsed.
Eventually, such a system will evolve further with the death of the
remaining supergiant star. At this point, a neutron star pair, or even a
neutron star-black hole pair, is formed. As these tiny stellar remnants
orbit one another, calculations show that they should lose energy and spiral
together. At the point of collision they may release a giant Gamma Ray
Burst.
A potential future ESA mission, currently undergoing technological
development, hopes to detect nearby neutron star pairs. Laser Interferometer
Space Antenna (LISA) will find them by spotting the gravitational waves they
radiate as they spiral together.
In the meantime, Integral has plenty of work to look for more supergiant
HMXBs and study the known ones further.
Notes for editors:
The following papers have been published today in the online issue of
Astronomy & Astrophyiscs:
'Multi-wavelength observations of Galactic hard X-ray sources discovered by
Integral.'
I. The nature of the companion star by S. Chaty, F. Rahoui, C. Foellmi, J.A.
Tomsick, J. Rodriguez, Walter
II. The environment of the companion star by F. Rahoui, S. Chaty, P.-O.
Lagage, E. Pantin
For more information:
Sylvain Chaty, University of Paris Diderot, France
Email: Chaty @ cea.fr
Christoph Winkler, ESA Integral Project Scientist
Email: Christoph.Winkler @ esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMSWO1YUFF_index_1.html ]