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All Was Quiet in the Galactic Centre.
For a brief time in April 2006, the active region surrounding the supermassive black hole at the heart of the Milky Way settled down. Ten different sources of high energy rays all faded away temporarily, and ESA's Integral probe was able to capture images of less bright regions, which weren't completely obscured by the bright objects in their vicinity.
Integral normally keeps track of about 80 bright X-ray objects near the galactic core. These are mostly X-ray binaries, where a regular star is locked in orbit with a collapsed star, like a white dwarf, Neutron star, or even black hole. If the two objects are close enough, gas is pulled off the star, and spirals onto the collapsed partner. This material heats up to over a million degrees, and causes it to emit high energy X-rays.
It was a completely random event that these normally bright objects dimmed down briefly, but Astronomers jumped at the opportunity to look for fainter objects which are normally obscured. They're hoping to turn up additional X-ray binaries, or high-energy radiation from giant molecular clouds. They might even be able to detect high-energy radiation around the Milky Way's supermassive black hole.
Integral sees the Galactic centre playing hide and seek.
ESA's gamma ray observatory Integral has caught the centre of our Galaxy in a moment of rare quiet. A handful of the most energetic high-energy sources surrounding the black hole at the centre of the Galaxy had all faded into a temporary silence when Integral looked. This unusual event is allowing Astronomers to probe for even fainter objects and may give them a glimpse of matter disappearing into the massive black hole at the centre of our galaxy.
The Galactic centre is one of the most dynamic places in our Galaxy. It is thought to be home to a gigantic black hole, called Sagittarius A* (pronounced 'A star'). Since the beginning of the Integral mission, ESA's gamma ray observatory has allowed Astronomers to keep watch on this ever-changing environment.
Integral has discovered many new sources of high-energy radiation near the galactic centre. From February 2005, Integral began to regularly monitor the centre of the Galaxy, and its immediate environment, known as the Galactic bulge.
Erik Kuulkers of ESA's Integral Science Operations Centre, ESAC, Spain, leads the Galactic bulge monitoring programme. Integral now keeps its high-tech eyes on about 80 high-energy sources in the galactic bulge. "Most of these are X-ray binaries," says Kuulkers.
X-ray binaries are made up of two stars in orbit around one another. One star is a relatively normal star; the other is a collapsed star, such as a white dwarf, neutron star or even a black hole. If the stars are close enough together, the strong gravity of the collapsed star can pull off gaseous material from the normal star. As this gas spirals down around the collapsed star, it is heated to over a million degrees centigrade and this causes it to emit high energy X-rays and gamma rays. The amount of gas falling from one star to the other determines the brightness of the X-ray and gamma-ray emission.
The fortuitous dimming allows Astronomers to set new limits on how faint these X-ray binaries can become. It also allows a number of new investigations to be undertaken with the data.
Integral's Galactic bulge monitoring programme will continue throughout this year. The data is made available, within a day or two of being collected, to the scientific community via the Internet from a dedicated webpage at the Integral Science Data Centre (IDSC), Geneva, Switzerland. This way, anyone interested in specific sources can watch for interesting changes and trigger follow up observations with other Telescopes in good time.
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Original Source: ESA News Release
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