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Black holes suck stuff in, blow it away
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13:10, November 08, 2007

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Black holes often are thought of as endless pits in space and time that destroy everything they pull toward them, but new research reveals they can also blow things away.

Scientists think supermassive black holes are at the heart of many -- if not all -- large galaxies. These holes suck gas inward, which accumulates into rapidly spinning, glowing disks. Astronomers have long thought that such "accretion disks" give off mighty winds that shape the host galaxies, profoundly influencing how they grow.


The artist's concept chronicles the star being ripped apart and swallowed by the cosmic beast over time. First, the intact sun-like star (left) ventures too close to the black hole, and its own self-gravity is overwhelmed by the black hole's gravity. The star then stretches apart (middle yellow blob) and eventually breaks into stellar crumbs, some of which swirl into the black hole (cloudy ring at right).(Xinhua/Reuters Photo)

"In the early universe, galaxies formed from clumps of gas coagulating from mutual gravitational attraction. If unhindered, they would have formed rather bigger structures than what we see today," said astrophysicist Andrew Robinson at the Rochester Institute of Technology in New York. "But if we take into account these winds blowing away surrounding gas, that could help explain the galaxy sizes we see."

Scientists had only theorized that accretion disks launched these winds. No one had actually seen this happen.

"These accretion disks are comparable in size to our solar system -- big for us, but on the scale of galaxies they're really tiny, and far away to boot, making it virtually impossible to distinguish any details such as winds," Robinson said.

To attempt to observe the winds, Robinson and his colleagues investigated a galaxy roughly 3 billion light years from Earth using the William Herschel Telescope on the Canary Islands off the coast of Africa. At the core of that galaxy lies a quasar, an extremely powerful source of radiation as bright as up to 1 trillion suns that originates from the superheated gas of a black hole's accretion disk.

The researchers discovered that light from the quasar was scattered by electrons in super-fast gas. The specific way in which this light was scattered suggests the gas was rotating at speeds similar to the accretion disk's rate of spin. In other words, they confirmed the accretion disk was launching wind.

The researchers will next try to find out if these disk winds are launched only when the black hole is growing rapidly, or just by quasars, which have the most massive black holes, or by all active galactic nuclei.

Source:Xinhua/Agencies




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