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A black hole in Earth’s backyard

Artistic depiction of the black hole Gaia BH1 and its companion star

International Gemini Observatory / NOIRLab / NSF / AURA / J. da Silva / Spaceengine / M. Zamani

Black holes with a relatively modest mass of just a few dozen times greater than the Sun are common. There are an estimated 100 million of them in the Milky Way alone. They are almost always active, swallowing the mass of the star that accompanies them and emitting X-rays in the process. Using a telescope in Hawaii, USA, an international group led by astrophysicist Kareem El-Badry from the Harvard-Smithsonian Center for Astrophysics identified the closest of these black holes to Earth. Dubbed Gaia BH1, its mass is equivalent to 10 Suns and is 1,600 light-years away from Earth, three times closer than the black hole previously considered the closest (Monthly Notices of the Royal Astronomical Society, November 2). It is located in the direction of the constellation Ophiuchus and is actually a dormant black hole. This means it is not consuming the star orbiting around it and thus does not emit X-rays. It was only detected because it has altered the trajectory of its companion.