Astronomers discover the closest black hole to Earth

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WASHINGTON – Astronomers have spotted the closest black hole to Earth ever discovered and are surprised by its living conditions – living harmoniously with two stars in a remarkable celestial marriage that can end in an unpleasant break.

The black hole, at least 4.2 times the mass of the sun, is linked by gravity to two stars in a so-called triple system about 1,000 light years from Earth, researchers said on Wednesday.

“Just around the corner” in cosmic terms, said Chile-based European Southern Observatory astronomer Thomas Rivinius, lead author of the study published in the journal Astronomy & Astrophysics.

A light year is the distance traveled by light in a year, 5.9 trillion miles (9.5 trillion km).

Black holes are extremely dense objects with gravitational forces so powerful that even light cannot escape. Some are monstrous like the one in the center of our galaxy 26,000 light years from Earth, or four million times the mass of the sun.

So-called stellar mass black holes, like the newly discovered ones, have the mass of a single star. It probably started life as a star up to 20 times the mass of the sun which collapsed in a black hole at the end of its relatively short lifespan.

This triple system, called HR 6819, can be seen from the Earth’s southern hemisphere with the naked eye, in the constellation Telescopium. Until now, the nearest known black hole was perhaps three times further away.

Only a few dozen black holes of stellar mass were known before. But there may be hundreds or billions of them in the Milky Way, said astrophysicist and co-author of the study Petr Hadrava of the Czech Academy of Sciences.

This black hole, detected with the help of an observatory in Chile, is careful with its manners and has not shredded its two partners: stars about five or six times the mass of the sun. At least not yet.

“The formation of a black hole is a violent process, and most models would not have predicted that a triple system could survive this, but rather fly away,” said Rivinius.

The black hole is a pair with one of the two stars, as close to each other as the Earth is in the sun. The other star is much further away, orbiting the pair. This star turns so fast that it is misshapen, bulging at the equator.

The two stars are far enough from the black hole not to shoot them matter. But in a few million years, the nearest star is expected to grow in size as part of its life cycle.

“What happens then is uncertain,” said Rivinius. “The most spectacular result would be that the black hole ends up with this star inside.”

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