A recent study by researchers at the Harvard-Smithsonian Center for Astrophysics and published in the journal Nature advances the discovery of a new type of intermediate-sized black hole.
Black holes are among the most mysterious celestial objects in the Universe. Most fall into two categories: « small » stellar black holes dozens of times heavier than our Sun and so-called « supermassive » black holes that can weigh the equivalent of millions or even billions of times the mass of the Sun. . A research team from the Harvard-Smithsonian Center for Astrophysics announces in the journal Nature that they have discovered a type of intermediate black hole with 2,200 solar masses hidden in the center of the globular cluster 47 of the Toucan, a dense cluster of stars located about 13 000 light years from Earth.
Researchers had already predicted the presence in the Universe of these intermediate black holes weighing between 100 and 10,000 times the mass of the Sun and suspected the presence of a handful of potential candidates. They believe these medium-sized black holes hold valuable clues as to how the supermassive black holes at the center of nearly all galaxies formed to reach such gigantic sizes that cannot be explained by our current understanding of physics. .
» We want to find intermediate-mass black holes because they are the missing link between stellar-mass black holes and supermassive black holes. », explains Bulent Kiziltan, of the Harvard-Smithsonian Center and lead author of this study. » These intermediate black holes could be the primordial seeds of the monsters we see at the center of galaxies..
The 47 Toucan cluster is dense, very dense, and researchers estimate it houses thousands of stars and about two dozen pulsars in a “ball” just 120 light-years in diameter. Researchers have long suspected the presence of a black hole at its center, but the absence of gas at the heart of the cluster has long left astronomers blind. Without material to « swallow », the black hole does not emit X-rays. Another strategy would be to spot the presence of a black hole betrayed by its influence on the surrounding stars – as was done to spot the black hole at the center of our galaxy. However, the Toucan 47 cluster is so full of stars that again the method does not work.
So how? For this study, the team took two different approaches. The first concerns the motions of the stars in the cluster. The cluster environment is so dense that massive stars tend to sink towards the center of the cluster. The intermediate black hole at the center of the cluster acts like a « cosmic spoon » stirring that center. As a result, stars are thrown at great speeds over great distances. Using computer simulations of stellar movements and distances and comparing them with observations in visible light, the researchers then detected the presence of the black hole.
The second approach focuses on pulsars which are the compact remnants of stars whose signals are easy to detect. These objects are also influenced by the gravitation of the intermediate black hole and these pulsars are repelled far from the center of the cluster compared to the predictions, again betraying the presence of a black hole. Using computer models, they were then able to calculate the mass of this black hole: approximately 2,200 solar masses. Taking into account the margin of error, the researchers suggest that the ogre could reach 3,700 solar masses, but does not drop below 1,400 solar masses.
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