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Stellar Black Hole is Most Massive Known in Milky Way
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
28 November 2001
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black_hole_011128 The largest stellar black hole ever detected in the Milky Way Galaxy has been examined by an international team of researchers using the European Southern Observatory's Paranal telescope in Chile. The astronomers determined that the black hole is 14 times more massive than our Sun. Most known stellar black holes, thought to be created when an aged star collapses, are about half that massive. Black holes are super-dense objects that serve as gravity wells. Once inside a black hole nothing, not even light, can escape. Much larger black holes often reside at the centers of galaxies. These behemoths, known as supermassive black holes, can contain the mass of millions or billions of stars. One is thought to anchor our Milky Way.The most energetic supermassive black holes, which are actively consuming matter and spewing X-rays into the universe, are called quasars. Most quasars are ancient, billions of years old and hence billions of light-years away. The newly identified stellar black hole is one of a special class of objects called microquasars. It behaves just like a miniature version of a quasar, eating voraciously and dishing out X-ray energy from superheated gas that approaches the speed of light just before it is consumed. The microquasar siphons mass from a companion star in a common arrangement known as a binary system. This system, first discovered in 1994, is named GRS 1915+105. It is about 40,000 light-year away and is located near the main plane of the Milky Way Galaxy. Gas and dust in that plane hide the object from our view in visible light. But space-based observations had previously detected energetic bursts of X-rays coming from the system. In the new work, researchers studied the system in infrared light. Though most of this light is also blocked by intervening gas and dust, a bit of it gets through and can be detected with a large telescope. The telescope at Paranal is very large. In fact, its lens is 27 feet in diameter (8.2 meters) and it is called the Very Large Telescope. The infrared observations allowed the astronomers to understand the chemistry of the donor star, which provided clues to its mass and size. They say the star is of relatively low mass, and that it feeds the black hole with a steady flow of gas, most of which spirals inward in what's known as an accretion disk. Analysis of the orbital motion of the star, combined with its estimated mass, made it possible to calculate the mass of the black hole. Because black holes can't actually be seen, the researchers note that it still remained to be proven whether or not the system really contains one.The research was conducted by Jochen Greiner and Mark McCaughrean of the Astrophysical Institute in Potsdam, Germany, and Jean-Gabriel Cuby of the European Southern Observatory. More About Black Holes: Astronomy News by TopicThis Week in Science & Astronomy: News Briefs
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