Wide-field image of QV Telescope (center) in the constellation Telescopium. Credit: ESO / Digital Sky Survey
Black holes have a reputation for being ravenous monsters that shatter stars and wreak easily recognizable havoc throughout the universe. However, most of them are quite quiet and difficult to detect. As such, astronomers haven’t found many of these objects close to Earth, but a team from the European Southern Observatory (ESO) has found one that is much closer than any previously recorded black hole. It is only 1,000 light years away in the constellation Telescopium. Despite the name, you don’t actually need a telescope to view this solar system.
Detecting black holes is more difficult than you think. A black hole is, by definition, black – they do not release any detectable energy because everything that passes through the event horizon remains inside it. The characteristic X-ray signature of black holes comes from super-hot material spiraling toward the event horizon in the accretion disk. If black holes are not actively ‘fed’, they are effectively invisible. It took months of observations with the MPG / ESO 2.2-meter telescope at the La Silla Observatory in Chile to confirm that there was a black hole lurking in the HR 6819 system (also known as the QV Telescope).
The key to identifying the black hole HR 6819 was the effect it has on the two main sequence stars of the system. We can see how these stars move through space, and gravitational interactions make it clear that it is not a binary system, but a trinary with two “normal” stars and a black hole. Based on the behavior of the two stars as they orbit the invisible mass every 40 days, the ESO team estimated that the third invisible element has about four times the mass of the sun. That can only be a black hole.
Before this discovery, the closest known black hole was about 3,000 light-years away in the constellation Monoceros. Naturally, the black hole HR 6819 cannot be seen even with the most powerful telescopes in the world. However, you can see both stars with the naked eye, as long as you are in the southern hemisphere.
QV Telescope might not enjoy the distinction of being the closest black hole for a long time. ESO believes this discovery lays the groundwork for finding more invisible black holes in nearby solar systems. As long as there is a visible star in the same system with a black hole, it should be possible to use its orbit to identify its invisible companion.