Astronomers know a star must be close to a black hole because the star ends up moving really slow

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The Milky Way Galaxy is thought to contain hundreds of millions of black holes. But only a few dozen have revealed themselves—through the x-ray glow of hot gases that surround them. Now, astronomers have found a “dark” black hole only 1000 light-years away from Earth—just down the road in galactic terms. It is the closest black hole to our planet ever found, in a star system that is visible to the naked eye. “They have good evidence,” says Todd Thompson, an astronomer at Ohio State University, Columbus. “I believe them.” The invisible nature of most black holes frustrates astronomers, who can learn about this final stage of stellar evolution only from the few dozen that have been found heating up an “accretion disk”—swirling gas they gobble up. Recently, however, astronomers have found several naked, nonaccreting candidates, using a technique borrowed from exoplanet searches. Exoplanet hunters look for periodic shifts in the frequency of the light from stars as it moves toward and away from Earth.

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