Stellar-mass black holes form when massive stars reach the end of their lives and collapse under their own gravity. In a binary system (a system of two stars rotating around each other), this process leaves a black hole orbiting with a bright companion star.
Sometimes this type of black hole becomes “dormant”, not emitting the usual high levels of X-ray radiation, which is how they are normally detected. Now one has been found outside the Milky Way.
An international team of astronomers known as the “black hole police”, which has refuted several discoveries of this type of object, has detected an inactive stellar-mass black hole in the Large Magellanic Cloud, a galaxy near 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, our team has come together to publicize the discovery of a black hole rather than refute it; we have identified a needle in a haystack,” said lead author Tomer Shenar, who began the study at the KU Leuven center (Belgium). and now has a Marie-Curie Fellowship 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 system, consisting 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 bigger than The hole.
“It’s amazing that we hardly know about the existence of these dormant black holes, given how common the astronomical community assumes they are,” says co-author Pablo Marchant of 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 these kinds of binary black hole systems,” adds co-author Julia Bodensteiner, a researcher at the European Southern Observatory (ESO) in Germany, who was thrilled when she learned of the data. on VFTS 243, “which I believe is the most compelling candidate reported to date.”
In the Tarantula Nebula
To find this binary system, the collaboration searched nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, focusing on those that may have black hole 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 disproven possible black holes for the past few years, I was extremely skeptical of this discovery,” insists Shenar. The skepticism was shared by co-author Kareem El-Badry of the Harvard & Smithsonian Center for Astrophysics, who Shenar calls the “black hole destroyer.” find a plausible explanation for the data that did not involve a black hole,” says El-Badry.
The discovery also gives the team 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,” says Shenar, who recalls that the evidence for “this ‘direct collapse’ scenario is not emerged only recently, but arguably our study provides one of the clearest indications, and it 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 FLAMES (Fiber Large Array Multi Element Spectrograph) instrument on ESO’s Very Large Telescope (VLT) 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 in the Large Magellanic Cloud”. “Astronomy of nature”, 2022.