Astronomers find closest black hole to Earth

A team of astronomers from the European Southern Observatory (ESO) have discovered the closest black hole to planet Earth, lying 1,000 light-years away. It is part of a star system that can be seen with the naked eye.

"This system contains the closest known black hole to Earth that we know of," said ESO astronomer Thomas Rivinius, who led the study that was published in the science journal Astronomy & Astrophysics on Wednesday.

The previously closest black hole to planet Earth is thought to be about three times further away, about 3,200 light-years, said Rivinius. One light-year equals around 9.5 trillion kilometers (5.9 trillion miles).

The new black hole, which measures some 40 kilometers (25 miles) in diameter, is located in the constellation of Telescopium, in the Southern Hemisphere.

Astronomers from ESO and other institutes spotted it using a 2.2-meter telescope at ESO's La Silla Observatory in Chile.

Read more: Snapshot of the black hole

Hidden black holes

It is difficult to find black holes because they take in everything in their surroundings, even light. Astronomers usually only discover them when they disrupt their nearby environment, such as gobbling up sections of a partner star.

Astronomers think most black holes, including this newly discovered one, do not have anything close enough to swallow, meaning most of them go undetected.

But scientists found this one while they were observing a system called HR 6819, as part of a study of double-star systems.

The astronomers found that every 40 days, one of the two visible stars orbits an unseen object, while the second star is at a large distance from this inner pair. From this observation, the scientists concluded it there must be a black hole.

Read more: Astronomers detect biggest explosion since Big Bang

Seen with the naked eye

The two stars in HR 6819 can be seen in the Southern Hemisphere without using a telescope.

"We were totally surprised when we realized that this is the first stellar system with a black hole that can be seen with the unaided eye," said Petr Hadrava, emeritus scientist at the Academy of Sciences of the Czech Republic, and co-author of the research.

Astronomers hope that the discovery of this black hole will provides clues about where the many hidden black holes in the Milky Way might be.

"Knowing what to look for should put us in a better position to find them," Rivinius said.

kmm/sms (AP, dpa)

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