(sda) This is what the discoverers around Thomas Rivinius from the European Southern Observatory ESO report in the journal “Astronomy & Astrophysics”.
The two companion stars can already be seen with the naked eye – but only from the southern hemisphere. For comparison: the earth’s home galaxy, the Milky Way, has a diameter of approximately 120,000 light years. A light year is the distance that light travels in one year.
The team had originally examined double stars. The analysis of the system with the catalog number HR 6819 in the southern constellation Telescopium surprisingly showed that there must be a third celestial body: One of the two visible stars orbits an invisible object with at least four times the mass of our sun every 40 days.
“An invisible object with a mass that is at least four times the size of the sun can only be a black hole,” Rivinius emphasized in an ESO announcement. “This system contains the black hole closest to Earth that we know of.”
Thanks to the comparatively short distance of the system, the two companion stars can be seen on dark, clear nights from the southern hemisphere without any aids, explained the ESO. “We were completely surprised to find that this is the first black hole star system to be seen with the naked eye,” said co-author Petr Hadrava, emeritus scientist at the Czech Academy of Sciences.
Unlike most other known specimens of this size, the black hole in the triple system is actually black and invisible. This is due to the fact that no matter is currently being absorbed from the environment.
Most of these so-called stellar, star-sized black holes have drawn attention to themselves through the bright X-rays that emanate from matter before it disappears into them again. Inactive, silent black holes, on the other hand, only reveal themselves through the effect of gravity, for example by a visible star orbiting them as in this case.
According to ESO, only a few dozen black holes have been discovered in the Milky Way. Astronomers hope that the current discovery will help track down further silent black holes in our home galaxy. “There must be hundreds of millions of black holes, but we know of very few,” said Rivinius. “If we know what to look for, we should be better able to find it.”
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