And the best part is, you can see it. A newly discovered black hole may be Earth’s closest black hole, and even without a telescope, you can see its celestial home in the night sky.
The black hole in the southern constellation of Telescopium, which lurks 1,000 light-years from Earth, belongs to a system of two companion stars that are bright enough to be observed with the naked eye.
Astronomers found this black hole when they observed what they believed was just a binary star system, or two stars sharing a common mass center. Researchers were using the 2.2-meter MPG / ESO telescope at Chile’s La Silla Observatory to observe the pair, known as HR 6819, as part of a larger review of double-star systems. As their findings were analyzed, the researchers were surprised to discover that the device hid a third object: a black hole.
While the astronomers were unable to directly observe the black hole, based on their gravitational interactions with the other two bodies in the system they were able to infer its presence. They were able to chart the orbits of the stars by studying the system for several months and found out that another huge, unknown object functioning in the system.
The observations also revealed that one of the two stars orbits the invisible object every 40 days, while the other star hangs itself from the black hole at a much greater distance. He determined that the object is a stellar-mass black hole— a black hole arising from a dying star’s collapse — that is about four times the size of the sun.
“An invisible object with a mass at least four times that of the sun can only be a black hole,” Thomas Rivinius, a scientist with the European Southern Observatory who led the new study, said in a statement. “This system contains the nearest black hole to Earth that we know of,” he added.
Following the black hole of HR 6819 the closest known black hole in the constellation Monoceros is around 3,000 light-years away from Earth. But there may also be others lurking much closer that have yet to be discovered; astronomers believe that our galaxy alone contains millions of black holes.
The black hole in HR 6819 is one of the first stellar-mass black holes discovered in our galaxy that doesn’t emit bright X-rays when interacting violently with its companion stars, and the finding may help researchers locate other similarly “quiet” black holes in the Milky Way, the statement says.
“There must be hundreds of millions of black holes out there, but we know about only very few,” Rivinius said. “Knowing what to look for should put us in a better position to find them.”
How to see HR 6819
While you might not be able to see the black hole from your home while stargazing, skywatchers in the Southern Hemisphere can see the stars in the night sky in the HR 6819 system without the help of binoculars or 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,” Petr Hadrava, a scientist emeritus at the Academy of Sciences of the Czech Republic in Prague and co-author of the study, said in the statement.
The duo appears in the modern constellation of Telescopium as a single, fifth-magnitude star, close to the border with Pavo’s constellation, the peacock. The faintest objects visible to the human eye are at magnitude 6.5 on the magnitude scale, in which smaller numbers signify brighter objects. Actually shining at magnitude 5.4—the dimmest visible planet, just slightly brighter than Uranus— HR 6819 is just barely bright enough for our eyeballs.