-
- ATLANTA
(Reuters) - Three
monster black holes have turned up in Earth's cosmic
neighborhood, astronomers
reported on Thursday, prompting questions
about whether black holes are
born before the galaxies that contain
them.
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- The
new trio of so-called supermassive black holes are
in the
constellations Virgo and Aries, between 50 million and 100 million
light years from Earth. Even though a light year -- the distance light
travels in a year -- is about six trillion miles, these distances are just
around the corner by celestial standards.
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- Their proximity is not unusual,
but their mass is: Each
weighs between 50 million and 100 million times
the mass of our sun. That
puts them in a comparatively small club of
giant black holes. Only 20 are
known to exist; most black holes weigh
just a few times the sun's mass.
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- Less than a decade ago, even
the notion of black holes
was a matter for debate. Now most astronomers
accept their existence but
question their role in the universe,
especially when it comes to the formation
of galaxies.
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- The massive black
holes are relics of quasars, Douglas
Richstone of the University of
Michigan said at a briefing at a meeting
of the American Astronomical
Society in Atlanta. Quasars are immensely
powerful bright objects that
shine as bright as a trillion suns within
an area the size of
Mars.
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- Quasars developed long before most stars formed in galaxies,
Richstone said. If these big black holes developed from quasars, as
Richstone
and his colleagues believe, they must have been present at
the height of
the quasar era -- when the universe was about a billion
years old.
-
- DID BLACK HOLES COME
FIRST?
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- This raises the question, Richstone said, of ``Which
comes first, the massive black hole or the galaxy that is its
host?''
-
- These astronomers believe that galaxies form and evolve
in
close relation to the massive black holes at their centers, and the
mass of black holes is related to the mass of the central part of the
galaxy.
-
- ``Radiation and high-energy particles released by the
formation
and growth of black holes are the dominant sources of heat and
kinetic
energy for star-forming'' in embryonic galaxies, Richstone said.
-
- Black holes are
mysterious matter-sucking drains in space,
taking in everything that
comes within their gravitational pull,not letting
even light
escape.
-
- But while black holes themselves cannot be seen, they
can often
be identified by the heat generated by matter as it swirls into
them.
-
- Stars speed up as they come relatively close to black
holes,
and their mass can be estimated by clocking the pattern of the stars'
velocity as they go by.
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- _____
-
- By Deborah
Zabarenko
1-15-00
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- ATLANTA (Reuters) - Some
black holes are naked vagrants drifting alone
through the Milky Way rather
than haloed objects waltzing around
companion stars, astronomers said on
Thursday.
-
- The discovery of two such lone
black holes could give
clues to what ultimately happens to big, normal
stars, the scientists said
in research presented at the annual meeting
of the American Astronomical
Society in Atlanta.
-
- Most black holes -- monstrous
matter-sucking drains in
space from which not even light can escape --
have been found in orbit
around normal stars. While these black holes
themselves are invisible,
astronomers determine their existence by
looking at the surrounding matter
just before it is gobbled up.
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- These two candidate
black holes were harder to spot,
since without a companion star, they
did not have much to ``eat'' and so
there was no sloppy, visible trace
of heated matter around the holes' rim.
-
- ``An isolated black hole is
actually a very dull object,''
Charles Alcock of the Lawrence Livermore
National Laboratory in California
said at a news conference with other
astronomers.
-
- He described a celestial object that simply drifts in
space --
``At some level, we're all drifting,'' Alcock said -- without
doing
much of anything.
-
- Astronomers using the orbiting Hubble Space Telescope
and
ground-based telescopes in Australia and Chile employed a technique
called gravitational microlensing to identify the two naked
candidates.
-
- To do this, they watched what happened to stars as they
passed
behind black holes. The powerful gravity of the black hole bends
the
light coming from the star, making it look like two banana-shaped
crescents
around where the black hole is suspected to be.
-
- The astronomers
studied 300 microlensing events to find
the two naked black hole
candidates.
-
- ``These results suggest that black holes are common and
that
many massive but normal stars may end their lives as black holes,''
David Bennett of the University of Notre Dame in Indiana told
reporters.
-
- This also could mean that black holes might be able to
form in
the collapse of isolated massive stars besides being produced by
interaction in a double-star system, the astronomers said.
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- Most galaxies,
including the Milky Way, which contains
the sun and our solar system,
are thought to harbor black holes at their
hearts. But all previous
black holes with about the same mass as a star
were found in orbit
around normal stars, making their presence known by
their effect on
their companion.
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