European astronomers have found a black hole about 1,000 light years away from Earth – closer than any other discovered to date.
Whilst 9.5 thousand, million, million kilometres might not sound very close, the next closest black hole discovered is about three times as far away as this one. The black hole at the centre of our galaxy is more than twenty five times as distant, and the furthest black hole ever detected is over 13 million times further away.
This newly-discovered black hole is part of a triple system called HR 6819, which until now was thought to be a double system consisting of only two stars. It is located in the constellation Telescopium.
Petr Hadrava, a scientist from the Academy of Sciences of the Czech Republic in Prague and a co-author of this new research, said that the team were “totally surprised” when they discovered that this was the first stellar system with a black hole that could be seen with the naked eye.
Nothing, not even light, can escape from inside a black hole. Despite the fact that they can’t be directly seen, they are usually quite easy to find. Only a couple of dozen black holes have been located in our galaxy, and most of these have been discovered by observing their surroundings. Many black holes interact with their environment in such a violent way that they can be detected by powerful X-ray emissions, which come as a result of matter being heated up as it is dragged towards the event horizon – quite literally ‘the point of no return’.
However the elusive black hole discovered in HR 6819 has proved to be unusual, as it is one of the first stellar-mass black holes to appear ‘truly black’.
Observations from the MPG/ESO 2.2-metre telescope at the European Southern Observatory’s La Silla observatory in Chile showed that the innermost star in HR 6819 orbits an invisible object every 40 days, whilst the outer star is seen to be far away from this inner pair. The team calculated the mass of this mystery object by studying the orbit of the star. ESO scientist Thomas Rivinius, who led the study published in Astronomy & Astrophysics, concluded that “an invisible object with a mass at least 4 times that of our Sun can only be a black hole”.
There are likely to be hundreds of millions of black holes in our Milky Way galaxy, but we know about very few of these. The discovery of this new hidden black hole will provide astronomers with useful clues about where there might be more of them. ESO astronomer and co-author of this study Dietrich Baarde said that finding this black hole, especially considering its proximity, shows that astronomers are seeing just “the tip of an exciting iceberg”.
There is already another more distant system of interest, LB-1, that astronomers think might contain a similar black hole.
The discovery of systems like these, which are made up of an inner pair and a distant star, could also tell us more about the violent cosmic mergers that produce ripples in space-time, known as gravitational waves, powerful enough to be detected on Earth.
Written by Anna Purdue and edited by Ailie McWhinnie.