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Opportunistic Black Holes Are No Suckers
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
05 June 2001
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Despite their common depiction as gravity sinks and suckers of all things, black holes are no more capable of luring distant meals than any other object of equal massDespite their common depiction as gravity sinks and suckers of all things, black holes are no more capable of luring distant meals than any other object of equal mass. They are opportunistic, however, and anything that comes close will be captured in a black hole's eternal clutches. "The total gravity of a celestial object depends only on its total mass, not its density," explained Paul Green of the Harvard-Smithsonian Center for Astrophysics. Black holes have plenty of mass, and they are incomprehensibly dense. Though they might occupy a space no larger than a small city (some theorists say the space is actually infinitely small) a black hole can harbor the same amount of material that exists in a normal star, or even that of thousands or millions of stars. But at long distances, a black hole's gravity is no more powerful or threatening than if an equivalent mass were rolled into a large but normal star. "If at midnight tonight, the Sun were to turn into a black hole, we wouldn't notice the difference," Green said. "The gravitational pull of the Sun would not change because its mass hasn't changed, so the orbit of the Earth would stay the same." However, Green continued, the Sun's total mass would then be packed into such a tiny space that anything passing within about a mile (1.5 kilometers) of it -- even light -- would be pulled in and lost forever. No word on what a day at the beach might be like under these circumstances.
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