- CHICAGO (AFP) -- Hundreds
of rogue black holes may be roaming around the Milky Way waiting to engulf
stars and planets that cross their path, US astronomers said Wednesday.
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- The astronomers believe these "intermediate mass"
black holes are invisible except in rare circumstances and have been spawned
by mergers of black holes within globular clusters -- swarms of stars held
together by their mutual gravity.
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- These black holes are unlikely to pose a threat to Earth,
but may engulf nebulae, stars and planets that stray into their paths,
the researchers said.
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- "These rogue black holes are extremely unlikely
to do any damage to us in the lifetime of the universe," said Kelly
Holley-Bockelmann, an assistant professor of physics and astronomy at Vanderbilt
University in Nashville, Tennessee.
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- "Their danger zone, the Schwarzschild radius, (or
gravitational radius) is really tiny, only a few hundred kilometers. There
are far more dangerous things in our neighbourhood."
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- The evidence for "intermediate mass" black
holes, as opposed to supermassive or stellar-mass black holes, is still
largely theoretical and therefore controversial. Only two tentative observations
of objects of this sort have been made to date.
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- But the theoretical case for them is strong, and X-ray
observations in recent years suggestive of their existence encouraged Holley-Bockelmann
and colleagues at the University of Michigan and Penn State University
to simulate what would happen if intermediate mass black holes combined
with stellar-sized black holes, which are plentiful in globular clusters.
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- Using sophisticated computer modeling, they calculated
that these mergers would generate hundreds of mid-size black holes, and
that the force of their combinations would catapult them out of the globular
cluster at speeds of up to 4,000 kilometers per second.
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- That would leave these black holes, each weighing several
times the mass of the sun, to careen around interstellar space, unattached
to any stellar system, at high speeds. Hence the term rogue.
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- Bockelmann presented her findings Wednesday at the 211th
American Astronomical Society meeting in Austin, Texas.
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- Separately, researchers reported that they have discovered
a new X-ray source in the galaxy of Centarus A.
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- The X-ray appeared in new observations of the galaxy
taken in 2007, but was not visible in a survey taken in 2003. The new ray
is much smaller than the X-ray jets that have long been a feature of the
galaxy, but it still glows brightly.
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- The new object is most likely a binary star system, the
researchers from Ohio State University said. The two stars probably formed
at the same time, with one much more massive than the other.
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- The more massive star evolved more quickly, and collapsed
to form a black hole. It is now slowly devouring its companion. Such binary
systems are thought to be rare.
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