WASHINGTON (Reuters) – Astronomers have discovered the closest black hole to Earth yet discovered and are surprised by the way they live – residing harmoniously with two stars in a remarkable celestial marriage that could end in an unpleasant rupture.
An artist's impression shows the orbits of the two stars and the black hole in the HR 6819 triple system, composed of an internal binary with a star (blue orbit) and a newly discovered black hole (red orbit), plus a third star in a wider orbit (also in blue), in this image released on May 6, 2020. ESO / L. Calcada / Disclosure via REUTERS
The black hole, at least 4.2 times the mass of the Sun, is gravitationally linked to two stars in a triple system about 1,000 light years from Earth, researchers said on Wednesday.
"Around the corner" in cosmic terms, said the European Observatory for Southern Europe astronomer Thomas Rivinius, lead author of the study published in the journal Astronomy & Astrophysics.
A light year is the distance that light travels in a year, 9.5 trillion kilometers.
Black holes are extraordinarily dense objects and have 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, which is four million times the mass of the sun.
The variety of gardens, the so-called black holes of stellar mass, like the newly discovered, has the mass of a single star. It probably started its life as a star with up to 20 times the mass of the sun that collapsed into a black hole at the end of its relatively short life.
This triple system, called HR 6819, can be seen with the naked eye in the southern hemisphere of the Earth, in the constellation Telescopium. Until now, the nearest black hole was perhaps three times as distant.
Only a few dozen star-shaped black holes were previously known. But there may be hundreds of millions or even a billion of them in the Milky Way, said the astrophysicist and study co-author Petr Hadrava of the Czech Republic Academy of Sciences.
This black hole, detected in an observatory in Chile, has good manners and does not destroy 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 it would disintegrate," said Rivinius.
The black hole forms a pair with one of the two stars, as close to each other as the Earth is from the sun. The other star is much further away, orbiting the pair. This star spins so quickly that it is misshapen, bulging at the equator.
The two stars are far enough away from the black hole that they are not removing material from them. 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 if the black hole ended with that star inside it."
Reporting by Will Dunham; Editing by Sandra Maler
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