Cosmic vicious cycle: Black holes are crashing into each other due to 'traffic jams' in space

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Supermassive black holes are giant voids in the heart of all large galaxies. They swirl around disks of matter, stars and their systems, and interestingly, other black holes, including the smaller, stellar mass ones.

"Traffic jams" caused by supermassive black holes in space might be causing collisions in other black holes.

According to a new study published in the Monthly Notices of the Royal Astronomical Society, the environment around a supermassive black hole is ideal for facilitating the growth of other black holes. 

Supermassive black holes are giant voids in the heart of all large galaxies. They swirl around disks of matter, stars and their systems, and interestingly, other black holes, including the smaller, stellar mass ones. The swirly behaviour around supermassive black holes can lead to a cosmic "traffic jam," which is integral in slowing down the orbits of stellar-mass black holes. When no longer moving from place to place, these black holes can collide, merging into one enormous black hole. 

Moreover, the process repeats due to the immense gravitational influence of the supermassive black holes, resulting in even more black-hole collisions that create larger and larger stellar-mass black holes over time.

Furthermore, an accretion disk, made of gas and dust, surrounds the supermassive black hole and gradually feeds it. These accretion disks glow brightly, creating an Active Galactic Nucleus (AGN) caused by the powerful tidal force generated by the supermassive black hole. 

Scientists from Monash University conducted the research where they looked at the dynamics found in accretion disks and their embedded black holes. According to the study, when stellar-mass black holes interact with the gas in the accretion disk, they can migrate through the disk, resulting in several such black holes accumulating in regions called "migration traps." Here, the probability of two stellar-mass black holes colliding and merging due to traffic jams is higher than anywhere else in the surrounding galaxy. 

The study's lead author, Evgeni Grishin, said, "We looked at how many and where we'd have these busy intersections. Thermal effects play a crucial role in this process, influencing the location and stability of migration traps. One implication is that we don't see migration traps occurring in active galaxies with large luminosity."

The findings give an understanding of how mergers between stellar-mass black holes proceed. They could also help advance gravitational wave astronomy in the future as these mergers create a burst of tiny ripples in spacetime known as gravitational waves.

"We're thrilled with the results, and we are one step closer to discovering where and how black holes merge in galactic nuclei. The future of gravitational wave astronomy and active galactic nuclei research is exceptionally promising," Grishin stated. "Despite these significant findings, much about the physics of black holes and their surrounding environments remains unknown," he added. 

(With inputs from agencies)

Trisha Pathak

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