Astronomers have discovered a black hole hiding closer to Earth than any found before it. Located about 1,000 light-years away in the constellation Telescopium, the black hole weighs in at some four times the mass of our sun, which means it’s only about 7.5 miles wide.
A team of researchers identified the black hole while tracking binary stars using a telescope at La Silla Observatory in Chile. When they looked at a double star system called HR 6819, they noticed that the inner star orbits quickly, while the outer star slowly chugs along.
This meant the stars are not just circling each other. Some unseen third object has to be located near the center of the system. The hidden object and the inner star dance around each other every 40 days. Meanwhile, the outer star slowly circles the pair much farther out. And because the invisible object is at least four times the mass of the sun, it can only be a black hole, the astronomers say.
Because black holes try not to betray themselves, finding a quiet one that is not actively devouring a neighbor is difficult. But even without emitting light themselves, the gravitational effects black holes have on other visible objects can be very revealing. For instance, on a dark, clear night in the Southern Hemisphere, you can actually see the two stars that orbit the black hole in HR 6819 with your naked eye.
“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,” study co-author Petr Hadrava said in a media statement.
