Have Astrophysicists Finally Solved the ‘Final Parsec Problem’ with Dark Matter?
Their new calculations reveal a previously overlooked behavior of dark matter particles that allows pairs of supermassive black holes to merge into one large black hole. The research is described in the paper “Self-interacting dark matter solves the final parsec problem of supermassive black hole mergers,” published this month in Physical Review Letters. This paper was published in Physical Review Letters. This paper was published in Physical Review Letters.
In 2023, astrophysicists detected a “hum” of gravitational waves traveling through the universe and postulated that this background signal emanated from the coalescence of millions of SMBH pairs. However, theoretical simulations showed that as these massive objects spiraled closer together, their approach stopped at a distance of about one parsec (about three light-years), preventing coalescence. This “last parsec problem” contradicted the theory that merging SMBHs are the source of gravitational wave background radiation and that SMBHs grow by merging low-mass black holes.
Co-author and postdoctoral fellow in the Department of Physics at the University of Toronto and McGill University and the Trottier Institute for Space Studies, “We show that the inclusion of previously overlooked dark matter effects can help supermassive black holes overcome this last parsec and merge.” He stated. Gonzalo Alonso-Alvarez said. Our calculations explain how that could happen, in contrast to what has been previously thought.”
Co-authors of the paper include James Klein, a professor in the theoretical physics department at McGill University and CERN in Switzerland, and Caitlin Dewar, a physics master’s student at McGill University.
SMBHs are thought to be at the center of most galaxies, and when two galaxies collide, their SMBHs fall into orbits around each other. Then, when two galaxies collide, their SMBHs enter orbits around each other, and as they rotate, they are slowed by the gravity of nearby stars, spiraling inward toward merging.
Previous models have shown that as SMBHs approach to within nearly one parsec, they begin to interact with the dark matter cloud or halo that surrounds them. The gravity of the spiraling SMBH throws dark matter particles out of the system, causing the dark matter to become sparse, preventing further energy loss from the pair and stopping the orbit from shrinking.
Although these models have ruled out an effect of dark matter on SMBH orbits, a new model by Professor Alonso Alvarez and his colleagues reveals that dark matter particles interact with each other to prevent dispersion. The density of the dark matter halo is sufficiently high that the interaction between the particles and SMBHs continues to degrade the SMBH orbitals, allowing them to merge.
Says Alonso Alvarez. ‘The possibility of dark matter particles interacting with each other is an extra element that we have assumed and that is not included in all dark matter models.’ Our contention is that only models that include that element can solve the final parsec problem.”
The background noise produced by these massive cosmic collisions consists of gravitational waves with much longer wavelengths than those first detected in 2015 by astrophysicists operating the Laser Interferometer Gravitational-Wave Observatory (LIGO). These gravitational waves were generated by the merger of two black holes, each about 30 times the mass of the Sun.
The Pulsar Timing Array reveals gravitational waves by measuring minute changes in the signal from pulsars, which are fast rotating neutron stars emitting powerful radio pulses.
The prediction we propose is that the spectrum of gravitational waves observed by the Pulsar Timing Array should be softer at lower frequencies,” says Klein. Current data already suggests this behavior, which may be confirmed by new data in the coming years.” ”
In addition to providing insight into the SMBH coalescence and gravitational wave background signal, the new results also provide a window into the nature of dark matter.
Our research is a new way to understand the particle nature of dark matter,” says Alonso Alvarez. We found that the evolution of black hole orbits is very sensitive to the microphysics of dark matter. In other words, we can use observations of the coalescence of supermassive black holes to understand more about these particles.”
The researchers found that the interactions between the dark matter particles they modeled can also explain the shape of the galaxy’s dark matter halo.
Says Alonso Alvarez. We found that the final parsec problem can only be solved if dark matter particles interact at a rate that changes the distribution of dark matter on a galactic scale.” This was unexpected because the physical scales at which this process occurs are more than three orders of magnitude apart. It’s exciting,” he said.
Source: Have Astrophysicists Finally Solved the ‘Final Parsec Problem’ with Dark Matter?
Watch And Listen To Gravitational Waves Arriving From Every Direction Of The Universe
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