It's a small revolution in the world of astronomy.
Astronomers have directly detected a black hole in a very young star cluster outside our galaxy for the first time, with a method promising new discoveries of these hard to pinpoint objects, according to a study Thursday.
“There are so many black holes in the Universe, but we don't know them because we can't see them,” says Sara Saracino, an astrophysicist at the University of Liverpool's Astrophysical Research Institute in Great Britain. -Brittany.
Their black color simply reflects the fact that these stars are, by definition, invisible.
Their gravitational force, the force that nails men to the surface of the Earth, is so powerful that not even light can escape.
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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 directly, when the proximity of the black hole with a nearby star disrupts the orbit of the latter.
The young and light black hole, a rare bird
Thanks to this technique, the team led by Sara Saracino discovered a black hole with a mass of about eleven suns, located in the star cluster NGC 1850 of the Large Magellanic Cloud, a galaxy "close" to the Milky Way, some 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 we have detected one with this technique in a very young cluster," outside our Milky Way, says the scientist, whose study appears in the Monthly Notices of the Royal Astronomical Society.
The very relative youth of the cluster - less than 100 million years old - is an asset, because "there is a very different kind of black hole, in the sense that they were formed very recently", explains Sara Saracino.
They 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 they are young and still “light-weight” is of even more interest to scientists, who seek to characterize the full range of black holes.
From “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.
To find the rare bird, 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 made it possible to "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 ”.