Gamma Ray Astronomy
PPARC simulation of the Microquasar LS5039 ENLARGE Image
This image was created using software developed by Dr. Rob Hynes of LSU.
Gamma-rays are produced in extreme cosmic particle accelerators such as supernova explosions and provide a unique view of the high energy processes at work in the Milky Way.
VHE (very high energy) gamma-ray astronomy is still a young field and the High Energy Stereoscopic System (H.E.S.S.) is conducting the first sensitive survey at this energy range, finding previously unknown sources.
The object that is producing the high energy radiation is thought to be a 'microquasar'. These objects consist of two stars in orbit around each other. One star is an ordinary star, but the other has used up all its nuclear fuel, leaving behind a compact corpse. Depending on the mass of the star that produced it, this compact object is either a neutron star or a black hole, but either way its strong gravitational pull draws in matter from its companion star. This matter spirals down towards the neutron star or the black hole, in a similar way to water spiraling down a plughole.
However, sometimes the compact object receives more matter than it can cope with. The material is then squirted away from the system in a jet of matter moving at speeds close to that of light, resulting in a microquasar. Only a few such objects are known to exist in our galaxy and one of them, an object called LS5039, has now been detected by the H.E.S.S. team.
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More from PPARC PressRelease:
Mystery compact object producing high energy radiation
Integral Catches a new erupting blackhole
ESA's gamma-ray observatory, Integral, has spotted a rare kind of gamma-ray outburst.
The vast explosion of energy allowed astronomers to pinpoint a possible black hole in our Galaxy.
The outburst was discovered on 17 September 2006 by staff at the Integral Science Data Centre (ISDC), Versoix, Switzerland.
"The galactic centre is one of the most exciting regions for gamma ray astronomy because there are so many potential gamma-ray sources," says Roland Walter, an astronomer at the ISDC, and lead author of these results.
In this case, the outburst continued to rise in brightness for a few days before beginning a gradual decline that lasted for weeks. The way the brightness of an outburst rises and falls is known to astronomers as a light curve. "It was only after a week that we could see the shape of the light curve and realised what a rare event we had observed," says Walter.
Comparing the shape of the light curve to others on file revealed that this was an eruption thought to come from a binary star system in which one component is a star like our Sun whereas the other is a black hole.
In these systems, the gravity of the black hole is ripping the Sun-like star to pieces. As the doomed star orbits the black hole, it lays down its gas in a disc, know as an accretion disc, surrounding the black hole.
Occasionally, this accretion disc becomes unstable and collapses onto the black hole, causing the kind of outburst that Integral witnessed. Astronomers are still not sure why the accretion disc should collapse like this but one thing is certain: when it does collapse, it releases thousands of times the energy than at other times.
Because such active star–black hole binaries are thought to be rare in the Galaxy, astronomers expect Integral to see such an outbursts only once every few years. That makes each and every one a precious resource for astronomers to study.
INTEGRAL catches a new erupting black hole
Additional Material to ESA's Press Release of 27 Nov. 2006