Simulations reveal secrets about the origin of intermediate-mass black holes in star clusters

Using computer models, scientists can simulate the formation of intermediate-mass black holes in star clusters. This opens up new ways to study mysterious objects. The universe is literally filled with black holes, from stellar masses to supermassive monsters. But one type remains elusive: the “average” black hole. They are called intermediate mass black holes. How common are they, how do they form, and where are they found? To answer these questions, astronomers have modeled possible formation scenarios.

Intermediate mass black holes lie within the mass gap between stellar masses and supermassive black holes. They have masses ranging from 100 to 100,000 solar masses. If they exist, do they indicate a hierarchical model of black hole formation, and do small black holes form from the collapse of supermassive stars? If so, then intermediate-mass black holes would form a kind of “transitional link” between stellar-mass black holes and supermassive black holes. If this idea is correct, could intermediate-mass black holes collide with each other and form the seeds of supermassive black holes?

At the same time, astronomers have enough data on stellar-mass black holes. They form when supermassive stars collapse. Supermassive black holes at the centers of galaxies most likely form through the accretion of matter, as well as mergers with other black holes. There is no doubt about the existence of intermediate-mass black holes, but observing them presents certain difficulties. That doesn’t mean they don’t exist. Observers have found candidates for intermediate-mass black holes in the Milky Way. They also appear to be present in active galactic nuclei, where accretion effects are observed.

Additionally, some ultra-luminous X-ray sources may also have these “intermediate” black holes. The Sloan Digital Sky Survey also found several potential candidates for strong emission in the X-ray range. X-ray emission is one of the features of activity around black holes. One of the most interesting observations involves gravitational waves emitted during the merger of two massive black holes. As a result, a black hole with a mass of about 150 times the mass of the Sun was formed – exactly the type of mass that can be classified as intermediate.

“Current observational limits do not allow us to say anything definitive about the number of intermediate-mass black holes between 1,000 and 10,000 solar masses,” Sedda explains. Science has a headache about their formation mechanism. Sedda and his team looked at star clusters that could be the birthplace of intermediate-mass black holes and created computer models that could simulate the formation of these mysterious objects using data from DRAGON-II. It is a collection of 19 computer models representing dense clusters of up to a million stars each.

The team also hypothesized what would happen after intermediate-mass black holes were born. They appear to be pushed out of their clusters by complex gravitational interactions or undergo “relativistic recoil” as they form. This prevents them from gaining weight. “Our model shows that even if seeds form naturally from interactions within star clusters, they are unlikely to become more massive than a few hundred solar masses, unless the parent cluster is extremely dense or giant.”