For the first time, researchers have found a sleeping black hole outside the Milky Way. Named VFTS 243, it is nine times the mass of our Sun and orbits a star in the Large Magellanic Cloud galaxy. The discovery came after six years of observations with the European Southern Observatory (ESO)’s Very Large Telescope (VLT) in Chile.
“Needle in the haystack”
The black hole is considered “asleep” because it does not emit high levels of X-ray radiation., which is how these structures are normally detected. This type of black hole is predicted in theory, but has never been identified. “We found a needle in a haystack,” said Tomer Shenar, a researcher at the University of Amsterdam who led the study, published in the journal Nature Astronomy.
Stellar-mass black holes are formed when massive stars reach the end of their lives and collapse under their own gravity. In a binary, a system of two stars revolving around each other, this process leaves behind a black hole orbiting a star. “We’ve been looking for these binary black hole systems for more than two years,” said Julia Bodensteiner, co-author of the study and a researcher at ESO.
The discovery gives the team unique insight into the processes that accompany the formation of black holes. Astronomers believe that a stellar-mass black hole forms when the core of a dying massive star collapses, but whether or not this is accompanied by a supernova explosion remains to be seen.
“The star that formed the black hole VFTS 243 appears to have completely collapsed, with no sign of a previous explosion”, explained Shenar. “Evidence for this ‘forward collapse’ scenario has emerged recently, but our study provides one of the most direct indications. This has huge implications for the origin of black hole mergers in the cosmos,” she added.
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