The closest black hole yet discovered is 1,560 light-years from Earth, a new study reports. The black hole, called Gaia BH1, is about 10 times the mass of the Sun and orbits the Sun’s star.
The most famous black holes steal and eat gas from the mass of stars. That gas forms a sphere around the black hole and shines brightly in X-rays. But hungry black holes are not the most common in our galaxy. There are many more quiet black holes that aren’t medium-sized, which astronomers have dreamed of finding for decades. Previous requests to find such black holes have only been unsupported (SN: 5/6/20; SN: 3/11/22).
So astrophysicist Kareem El-Badry and colleagues turned to data recently released from the Gaia spacecraft, which provide precise maps of the positions of billions of stars (SN: 6/13/22). A star orbiting a black hole in safe space will not be eaten, but will be pulled back and forth by the black hole’s gravity. Astronomers can detect the motion of the star and deduce the presence of a black hole.
Out of the hundreds of thousands of stars that seemed to have been pulled back by an invisible object, it seemed like one good candidate for a black hole. Follow-up observations with other telescopes support the idea of a black hole, the team reports on November 2 Monthly Notices of the Royal Astronomical Society.
Gaia BH1 is the closest black hole to Earth ever found – the closest is about 3,200 light-years away. But it’s probably not the closest we’ll ever find, or even the closest. Astronomers think there are about 100 million black holes in the Milky Way, but almost all of them are invisible. “They’re just separated, so we can’t see them,” says El-Badry, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Gaia’s next data release is from 2025, and El-Badry expects it to yield a larger black hole. Many things, he says, we think are nearer. “Like finding one…suggests there’s a bunch more to be found.”
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