A team of astronomers from the European Southern Observatory (ESO) and other institutes discovered a black hole located only 1,000 light years from Earth. The black hole is closer to our solar system than any other to date.
This newfound dark neighbor is at least 4.2 times more massive than the sun and lives with two ordinary stars whose funny orbits gave the presence of the black hole, astronomers report on May 6 in Astronomy & Astrophysics.
Astronomers discovered this black hole while studying what they thought was just a binary star system, or two stars orbiting a common center of mass. They were using the 2.2-meter MPG / ESO telescope at the La Silla Observatory in Chile to observe the binary, called HR 6819, as part of a larger study on double star systems.
Image credit: ESO/Digitized Sky Survey 2/Davide De Martin
When they analyzed their observations, the researchers were shocked to learn that a third object was hidden in the system: a black hole.
Astronomers expect the Milky Way to host between 100 million and one billion black holes with masses between a few and 100 times that of the sun. But most of these black holes are invisible.
“An invisible object with a mass at least four times that of the Sun can only be a black hole,” said astronomer Thomas Rivinius of the European Southern Observatory. Therefore, “this system contains the nearest black hole to Earth that we know of.”
If it’s lonely out there without a companion, you’ll never find it,” says Thomas Rivinius.
“We would have seen it if it was a normal star,” Rivinius says. “If it’s not a normal star, the only thing it can be otherwise is a black hole.”
The HR 6819 is close enough and its stars are bright enough that, on a dark and clear night in the southern hemisphere, the stars are visible to the naked eye, scientists say.
This artist’s impression shows the orbits of the objects in the HR 6819 triple system. (Image credit: L. Calçada/ESO)
The discovery could shed light on an unusual system in the Gemini constellation called LB-1. It has already been suggested that this system is composed of a star and an extremely massive black hole – a discovery that has drawn the attention of experts.
“We realised that another system, called LB-1, may also be such a triple, though we’d need more observations to say for sure,” said ESO astronomer Marianne Heida.
“LB-1 is a bit further away from Earth but still pretty close in astronomical terms, so that means that probably many more of these systems exist. By finding and studying them we can learn a lot about the formation and evolution of those rare stars that begin their lives with more than about eight times the mass of the Sun and end them in a supernova explosion that leaves behind a black hole.”