Astronomers have discovered the closest black hole to our solar system — it's just 1,000 light-years away.
Scientists from the European Southern Observatory (ESO) detailed the findings in a study published Wednesday in the journal Astronomy & Astrophysics.
Since black holes exert a force of gravity so strong that not even light can escape, you can't see them directly — but you can see some of the stuff that orbits them.
This wide-field view shows the region of the sky, in the constellation of Telescopium, where HR 6819 can be found. The triple system consists of two stars and the closest black hole to Earth ever found. ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
That's how the researchers stumbled upon this black hole. They were studying double-star systems and noticed that one of the stars they were watching was orbiting an invisible object every 40 days.
"An invisible object with a mass at least 4 times that of the sun can only be a black hole," Thomas Rivinius, an ESO scientist who led the study, said in a press release. He added, "this system contains the nearest black hole to Earth that we know of."
The below video shows what the astronomers saw: a star (blue) orbiting an invisible black hole (red), with another star (also blue) orbiting the inner pair. That makes this star system, called HR 6819, a triple system.
"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 at the Academy of Sciences of the Czech Republic in Prague and co-author of the research, said in the release.
The star system is close enough that people in Earth's southern hemisphere can spot the stars on a clear night.
"There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them," Rivinius said.
Dietrich Baade, an ESO astronomer on the research team, called the discovery "the tip of an exciting iceberg."
In fact, the researchers already have their eye on another two-star system, called LB-1, that could be hiding its own black hole.