Black hole detected for the first time in a star cluster

Astronomers have detected for the first time a black hole in a very young star cluster outside our galaxy, thanks to a method promising new discoveries of these difficult to pinpoint objects, a study reveals, Thursday, November 11.

“There are so many black holes in the Universe, but we don’t know them because we can’t see them”explained Sara Saracino, an astrophysicist at the Institute for Astrophysics Research at the University of Liverpool, UK. The black color attributed to them only reflects the fact that these stars are, by definition, invisible. Their gravitational force is so powerful that not even light can escape from them.

They can be detected indirectly, by the radiation emitted at their border when they absorb matter, or by gravitational waves caused, for example, by the fusion of two black holes. And if not more directly, when the proximity of the black hole to a nearby star disrupts the orbit of the latter.

“Small” black hole of eleven solar masses

Thanks to this last technique, the team led by Mr.^me Saracino discovered a black hole with a mass of about eleven suns, located in the NGC 1850 star cluster of the Large Magellanic Cloud, a galaxy close to the Milky Way, about 160,000 light years away. This “small” black hole slightly distorts its nearby star, which weighs five solar masses. “This is the first time that one has been detected with this technique in a very young cluster”, outside of our Milky Way, says the scientist, whose study appears in the Monthly Notices of the Royal Astronomical Society.

To find it, the scientists used MUSE, a wide-field spectrograph, installed only a few years ago on the Very Large Telescope of the European Southern Observatory (ESO) in Chile. It allowed“Observe a very populated area”, according to Sebastian Kammann, co-author of the study, quoted in an ESO press release, “With information on thousands of stars at once, ten times more than with any other instrument”.

The very relative youth of the cluster – less than 100 million years old – is an asset, because “We find there a kind of very different black holes, in the sense that they were formed very recently”, explains Sara Saracino. They thus did not have time to be expelled, “As is the case with very old star clusters”, nor especially to interact with each other.

The fact that he’s young and still ” lightweight “ Of particular interest to scientists, who seek to characterize the full range of black holes. From those with “stellar” mass, like the one identified by Sara Saracino’s team, to supermassives reaching several million solar masses, including “intermediaries”, the very existence of which remains disputed.