A dormant black hole discovered outside our galaxy

The bone stellar mass black holes they form when massive stars reach the end of their life and collapse under their own gravity. In one binary system (a system of two stars revolving around each other), this process leaves a black hole orbiting with a bright companion star.

Sometimes this type of black hole remains ‘idle’, it does not emit the usual high levels of X-rays, which is how they are normally detected. Now one has been found outside the Milky Way.

An international team of astronomers known as the ‘the black hole font‘, which refuted several discoveries of this type of object, detected an inactive stellar-mass black hole in the Large Magellanic Cloud, a neighboring galaxy to ours. Moreover, the star that gave birth to this hole disappeared without any sign of a powerful explosion, as published by the magazine natural astronomy.

For the first time, an inactive stellar-mass black hole, which does not emit the usual high levels of X-rays, has been discovered outside the Milky Way, in the nearby Large Magellanic Cloud; and as a companion has a blue star

“For the first time, our team has come together to publicize the discovery of a black hole rather than refute it; we identified a needle in a haystack”, emphasizes the main author, Tomer Shenarwho began his studies at the KU Leuven center (Belgium) and now benefits from a Marie-Curie scholarship at the University of Amsterdam (Netherlands).

Although other similar candidate black holes have been proposed, the team says this is the first inactive stellar-mass black hole to be unambiguously detected outside our galaxy. It is part of the VFTS 243 binary systemcomposed of a hot blue star with 25 times the mass of the Sun and a black hole, which is at least nine times the mass of the Sun. The star is about 200,000 times larger than the hole.

“It’s amazing that we barely know about the existence of these dormant black holes, given how common the astronomical community assumes they are,” says the co-author, Paul Marchant, from the KU Leuven. Dormant black holes are particularly difficult to detect because they interact little with their environment.

“For more than two years, we have been looking for this type of binary black hole systems,” adds the co-author, Julia Bodensteinerresearcher at the European Southern Observatory (ESO) in Germany, who was thrilled when she learned of the data on VFTS 243, “which in my opinion is the most compelling candidate reported to date”.

In the Tarantula Nebula

To find this binary system, the collaboration searched nearly 1000 stars massive in the Tarantula Nebula region of the Large Magellanic Cloud, focusing on those that may have black holes as companions. It is extremely difficult to identify them as black holes, since there are many alternative possibilities.

The study focused on the Tarantula Nebula, the most prominent object in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. / HIS

“As a researcher who has disproved possible black holes for the past few years, I was extremely skeptical of this discovery,” insists Shenar. The skepticism was shared by the co-author Kareem El Badry, from the Harvard & Smithsonian Center for Astrophysics (USA), which Shenar calls the “black hole destroyer”. “When Tomer asked me to review his findings, I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t implicate a black hole,” says El-Badry.

The star that gave birth to this black hole disappeared without any sign of a powerful explosion, a recently proposed example of a “direct collapse” with implications for how these objects form.

The discovery also provides the team with unique insight into the processes that accompany the formation of black holes. The astronomical community believes that a stellar-mass black hole forms when the core of a dying massive star collapses, but whether or not this process is accompanied by a powerful supernova explosion is unknown.

“The star that formed the black hole in VFTS 243 appears to have completely collapsed, with no signs of a previous explosion,” Shenar says, recalling that evidence for “this “direct collapse” scenario emerged recently, but our study provides perhaps one of the clearest indications; And that has huge implications for the origin of black hole mergers in the cosmos.

Six years of observations with the VLT

The black hole in VFTS 243 was found using six years of observations of the Tarantula Nebula by the instrument. FLAMES (Fiber Large Array Multi Element Spectrograph, fiber large array multielement spectrograph), installed in the Very Large Telescope (VLT) of ESO in Chile.

Despite the nickname “black hole police,” the team actively encourages scrutiny, debate with alternative models, and hopes their work will lead to the discovery of other stellar-mass holes orbiting massive stars. , thousands of which are predicted to exist in the Milky Way and the Magellanic Clouds.


Tomer Shenar et al. “A Silent X-Ray Black Hole born with a negligible kick in a massive binary within the Large Magellanic Cloud”. natural astronomy2022.

Rights: Creative Commons.

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