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Astronomy

The closest black hole to Earth was found in a star system you can see with the naked eye

This illustration provided by the European Southern Observatory in May 2020 shows the orbits of the objects in the HR 6819 triple system.

European astronomers have found the closest black hole to Earth yet, one of many more undetected black holes that could be found in the future.

A team of astronomers from the European Southern Observatory discovered the black hole just 1,000 light-years from Earth, said Dietrich Baade, co-author of a study published online Wednesday in the peer-reviewed journal Astronomy & Astrophysics. The astronomers found the invisible object while tracking two nearby stars in the constellation Telescopium that can be seen with the naked eye using the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile.

"We were not searching for it," Baade said. "It was a complete surprise."

The new black hole is part of a system called HR6819, which Baade said initially consisted of three stars before the most massive star collapsed in a supernova explosion and became a black hole.

Researchers observed that one of the remaining stars orbits an unseen object every 40 days. They were able to calculate that object's mass by studying the orbit of the inner star and were "stunned" to discover it was a black hole.

"It must be a black hole because only a black hole of that mass is invisible," Baade said.

The previous closest black hole is probably about three times further, about 3,200 light-years, according to ESO scientist Thomas Rivinius, who led the study.

Scientists have spotted only two dozen black holes in our galaxy, Baade said. Because black holes can't be seen directly, astronomers are typically able to detect them only when they are interacting violently with their environment, causing them to expel gas that glows in an X-ray.

"The black hole that we have found is different in that it is starving," he said. "This black hole is truly black."

Astronomers believe most black holes, like this newly discovered one, go undetected because they don’t have anything close enough to swallow. Baade said based on a "very quick, back-of-the-envelope estimate" he believes there may be a few more triple systems like this one nearby.

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"There must be hundreds of millions of black holes out there, but we know about only very few," Rivinius said in a statement. "Knowing what to look for should put us in a better position to find them."

Baade said they already have a lead on where the next black hole might be. Another system, called LB-1, may also be a triple star system, but more observations are needed to confirm whether it contains a black hole or a neutron star.

"We are all very excited," Baade said. "But one would like to have another one."

Contributing: The Associated Press

Follow N'dea Yancey-Bragg on Twitter: @NdeaYanceyBragg

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