Researchers knew they existed, but this is the first time they’ve discovered a “dormant” black hole. And for good reason, they are very difficult to detect.
SPACE – This is the first. A team of international experts has discovered a dormant black hole. They published their research in nature astronomy, last July 18. Named VFTS 243, it took them 6 years of observing with the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile, to find this black hole in the Large Magellanic Cloud, a neighboring galaxy to our own.
Finding an inactive black hole, a real headache
“We identified a needle in a haystack”says Tomer Shenar, lead author of the study. In general, we detect a black hole when a star revolves around it. The material that makes up this star is partially trapped by the black hole and it is by detecting the movements of this material that it emits X-rays that can be detected in space. But here, the black hole emits nothing, and for good reason: “The living star (about 25 times the mass of the Sun) is far enough away not to be eaten,” explains Hugues Sana of the University of Leuven and co-author of the study.
To find VFTS 243, the collaboration searched nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, looking for any that might have black holes as companions. But it is extremely difficult to identify these companions as black holes, since there are so many other possibilities.
“As a researcher who has debunked potential black holes in recent years, I was extremely skeptical about this discovery.”says Tomer Shenar. This skepticism was shared by co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian in the United States, which Tomer Shenar calls the “black hole destroyer”. ” When Tomer asked me to review his results, I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t involve a black hole. », explains Kareem El-Badry.
Different types of black holes
There are mainly two types of black holes. The one discovered is a stellar-mass black hole. This type of black hole has a mass that can be up to 20 times that of the Sun. It forms when the core of a star collapses, often causing an explosion called a supernova. But the phenomenon can vary, the test with VFTS 243 which has another peculiarity: the scientists did not detect any sign of explosion.
Maïca Clavel, an astrophysicist at the CNRS at the Institute of Planetology and Astrophysics in Grenoble, explains that this is a phenomenon that has already been theorized: “There are articles that say that if the star is really very massive, there is no freedom for the material to escape and therefore everything is really falling at once. »
The other type of black hole is said to be supermassive. They are at least a million times the mass of the Sun. If scientists don’t quite know how they formed, the main thing to remember is that they are at the center of galaxies. Ours, for example, the one in the center of the Milky Way is called Sagittarius A*
A supermassive black hole is powerful enough to swallow a star, but rest assured, when it comes to our galaxy and specifically the Sun, there’s not much to worry about, as Maïca Clavel details: “You really have to get very close to the black hole to get sucked in. However, the supermassive black hole at the center of our galaxy is 27,000 light-years from us. So if we went at the speed of light towards Sagittarius A*, it would take us 27,000 years to get there. Furthermore, our Sun orbits the center of our galaxy at about 220 km/s. So it’s not going in the right direction, or at the right speed. Therefore, there is no risk that we will meet the black hole in the center of our galaxy. »
There would be a third type of black hole located between those of stellar mass and supermassive. They are called intermediate black holes and would have a few thousand solar masses. Unfortunately, we have never discovered any.
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