An international team of astronomers has discovered, using the FEROS Optical Spectrograph of the MPG / ESO 2.2 m telescope at ESO’s La Silla Observatory, the closest black hole to our solar system. It is “only” 1,000 light years from Earth in the constellation Telescopium. It has a mass at least four times that of the Sun and about 25 to 30 kilometers in diameter. The region is part of a triple star system observable with the naked eye.
Astronomers expect the Milky Way to host between 100 million and 1 billion black holes with masses a few to 100 times that of the sun. But most of those black holes are invisible. “If you are alone without a partner, you will never find him, ” says astrophysicist Thomas Rivinius, of the European Southern Observatory in Santiago, Chile.
The few dozen small black holes seen so far interact violently with their surroundings, engulfing gas from a companion star and heating the gas until it emits X-rays. The closest known previous black hole is V616 Mon and it emits X-rays from about 3,200 light years away.
“There must be hundreds of millions of black holes out there, but we know very little about them . Knowing what to look for should put us in a better position to find them, ”continues Rivinius.
Now, the new black hole closest to us has been dubbed HR 6819 and, although it is invisible, it appears to have two companions : a star that the black hole orbits every 40 days and hotter than the sun and a massive star. and distant that spins so fast it’s almost breaking. Its discovery has been fortuitous. Tracking down what was previously believed to be a binary system, HR 6819, they discovered that the two main sequence stars appeared to be skewed. The analysis of the orbits showed that there were not two, but three objects that danced in orbit. Since the third object was invisible, it could only be a black hole, since no other object would create a system without emitting light. It is very small and silent and the first black hole we can find with two stellar companions visible to the naked eye.
It’s not the first time that by looking for strange-acting stars we’ve ended up finding black holes, but each of those systems we detect gives us more clues that can help us solve even bigger mysteries about the universe. For example, looking at how three bodies interact in a system containing a black hole could be important in understanding how multi-body systems cause collisions of black holes or neutron stars that generate gravitational waves.
This system also has the potential to explain other triple systems that we know of, including LB-1, located 2,300 light-years away from Earth. LB-1 appears to have a small star orbiting a very large black hole. But the black hole is too big to have formed from a supernova. Thanks to this discovery and what is to come, we could identify its origin.
“We realized that another system, called LB-1 , can also be triple, although we would need more observations to be sure,” said Marianne Heida, postdoctoral fellow at ESO and co-author of the article in the journal Astronomy & Astrophysics. “LB-1 is a bit further from Earth, but it is still quite close in astronomical terms, which means that there are probably many more of these systems. By finding and studying them we can learn a lot about the formation and evolution of these stars. rare that begin their lives with more than about eight times the mass of the Sun and end in a supernova explosion that leaves a black hole. “
Both HR 6819 and LB-1 may be more common than they appear.
If you want to observe the stars of this triple system, they are in the southern hemisphere, in the constellation of Telescopium and are visible with the naked eye in areas of low light pollution.
Referencia: “A naked-eye triple system with a nonaccreting black hole in the inner binary”, Astronomy & Astrophysics (2020). DOI: 10.1051/0004-6361/202038020
