There are stellar black holes that form when a massive star collapses at the end of its life. They are usually as heavy as stars, between three and about a hundred solar masses. There are massive black holes located in the centers of galaxies, weighing a few million or even billions of the mass of the Sun. But could there also be black holes with masses ranging from a few hundred to 100 thousand solar masses, or so-called IMBHs (intermediate-mass black holes)? So far there is no clear evidence of their existence. But the evidence is mounting. An international team led by Manuel Arca-Seda and Albrecht Kamla from the Max Planck Institute for Astronomy is using high-resolution numerical simulations to show that the smaller IMBHs arise naturally from high-energy interactions between stars within star clusters.

“Intermediate-mass black holes are difficult to observe,” explains Manuel Arca Seda, a physicist at the Gran Sasso Institute in L’Aquila, Italy, and lead author of the research article. Which was published in the Monthly Notices of the Royal Astronomical Society., According to a press release. “Current observational methods do not allow us to investigate the population of black holes with masses between 1,000 and 10,000 solar masses,” mainly because they have not yet been detected using telescopes or indirect techniques. There is currently hope that highly sensitive gravitational wave detectors will one day be able to provide evidence of the merger of such objects.

Astronomers have long suspected that medium-sized black holes could be found in dense star clusters. With the help of complex computer simulations, experts have now discovered a possible mechanism for how they form in such massive, young star clusters. And in fact: when single and binary star systems collide, increasingly massive stars are formed, which eventually become black holes. At this point they can absorb more massive stars and black holes, resulting in black holes with a mass of several hundred solar masses.

The most important result of the simulations: only a complex set of different interactions and fusion events leads to the target. However, the probability of reaching masses greater than a few hundred solar masses depends on the density and mass richness of the environment. Very violent exchanges can eject objects from the parent star cluster after only a few hundred million years.

However, an important scientific mystery remains unanswered: whether these intermediate black holes represent the link between stellar and supermassive black holes. However, the study leaves room for some speculation. “We need two components to understand better,” Seda explains. “On the one hand, we need to know one or more of the processes capable of forming IMBHs, and on the other hand, we need an explanation of what sustains the organisms in their environment.” The study provides useful evidence for the first component. The second aspect, on the other hand, imposes high demands on future simulations – more star clusters containing a much larger number of binary stars must be analyzed and processed.