SIGHTINGS



Three Monster Black
Holes Found
Near Earth
By Deborah Zabarenko
Link
1-15-00
 
 
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.
 
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.
 
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.
 
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.
 
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.
 
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?
 
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
 
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.
 
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.
 
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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