Researchers have found that elusive intermediate-mass black holes can form in dense star clusters containing anywhere from tens of thousands to millions of tightly packed stars called “globular clusters.”
An intermediate-mass black hole has a mass between 100 and 10,000 suns. They are heavier than solar-mass black holes, which have a mass range between 10 and 100 solar masses, but lighter than supermassive black holes, which have masses equivalent to millions or even billions of suns.
These cosmic mediators have proved elusive to astronomers, with the first example being found in 2012. Named GCIRS 13E, it has a mass 1,300 times that of the Sun and lies 26,000 light-years away, toward the galactic center. of Milk. Ways.
One of the mysteries surrounding intermediate-mass black holes concerns their formation. Stellar-mass black holes are born when massive stars collapse, and supermassive black holes grow from subsequent mergers of increasingly massive black holes. However, a star massive enough to die and create a black hole with thousands of solar masses must be extremely rare and must struggle to maintain that mass when it “dies”.
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To investigate the mystery of how these intermediate-mass black holes are created, a team of researchers performed the first star-by-star simulation of massive clusters. This showed that a dense enough molecular “birth nest” cloud of globular clusters could give rise to stars massive enough to collapse and create an intermediate-mass black hole.
“Previous observations have suggested that some massive star clusters, globular clusters, host an intermediate-mass black hole,” team leader and the University of Tokyo. scientist Michiko Fujii said in a statement. “Until now, there has been no strong theoretical evidence to show the existence of intermediate-mass black holes with 1000 to 10,000 solar masses compared to less massive (stellar masses) and more massive (supermassive) ones.
A chaotic birthplace for black holes
The term “birth nest” may conjure up images and feelings of warmth, comfort, and tranquility, but it could not be less appropriate for star formation in globular clusters.
These densely packed star conglomerates live in chaos and turmoil, with changes in density causing stars to collide and merge. This process results in stars clumping together in mass, thus increasing their gravitational influences, drawing more stars into their vicinity and thus prompting more and more mergers.
The distant collision and merger process that occurs in the hearts of globular clusters can lead to the creation of stars with masses equivalent to about 1000 suns. This mass is enough to create an intermediate-mass black hole, but there is a catch.
Astrophysicists know that when stars collapse to create black holes, much of their mass is blown away in supernova explosions or stellar winds. Previous simulations of the creation of intermediate-mass black holes have confirmed this, further suggesting that even stars as massive as 1000 solar masses would end up too small to create an intermediate-mass black hole.
To find out if a massive star could “survive” with enough mass to give birth to an intermediate-mass black hole, Fujii and his team simulated a globular cluster as it formed.
“We have, for the first time, successfully performed numerical simulations of the formation of globular clusters, modeling individual stars,” said Fujii. “By resolving individual stars with a realistic mass for each, we can reconstruct stellar collisions in a tightly packed environment. For these simulations, we have developed a new simulation code in which we can integrate millions of stars with high precision .”
In the simulated globular cluster, collisions and runaway mergers led to the formation of extremely massive stars that could carry enough mass to collapse and give birth to an intermediate-mass black hole.
The team also found that the simulation predicted a mass ratio between the intermediate-mass black hole and the globular cluster within which it formed. This report, as it turned out, agrees with actual astronomical observations.
“Our ultimate goal is to simulate entire galaxies by resolving individual stars,” Fujii explained. “It is still difficult to simulate galaxies the size of the Milky Way by resolving individual stars using currently available supercomputers. However, it would be possible to simulate smaller galaxies such as dwarf galaxies.”
Fujii and her team also intend to target clusters of stars that formed in the early universe. “Primary clumps are also places where intermediate-mass black holes can be born,” she said.
The team’s research was published Thursday (May 30) in the journal Science.
