University of Toronto Research: Dark Matter may solve the mystery of supermassive Black Hole mergers

Mysterious Dark Matter Research: A team of astrophysicists, including the University of Toronto postdoctoral fellow Gonzalo Alonso-Álvarez, has potentially solved one of the most perplexing problems in astrophysics: the "final parsec problem." This breakthrough could provide crucial insights into the behavior of supermassive black holes (SMBHs) and the mysterious dark matter surrounding them.

The Final Parsec Problem

The final parsec problem refers to a significant gap in our understanding of how supermassive black holes merge, each billions of times more massive than the Sun. Astrophysicists have long believed that gravitational waves detected across the universe result from millions of merging SMBHs. However, theoretical simulations have shown that their approach stalls when two SMBHs get within about one parsec (roughly three light years) of each other. This discrepancy has puzzled scientists for years, casting doubt on theories about the sources of gravitational waves and the growth of SMBHs through mergers.

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New Research Breakthrough

In a study recently published in Physical Review Letters, Alonso-Álvarez and his colleagues demonstrated that SMBHs can overcome the one-parsec barrier and merge into a single black hole. Their calculations reveal that previously overlooked interactions with particles within the vast cloud of dark matter surrounding these black holes play a critical role.

Dark Matter’s Role

"By including the previously overlooked effect of dark matter, we show that supermassive black holes can overcome this final parsec of separation and coalesce," explains Alonso-Álvarez, who is a postdoctoral fellow at both the University of Toronto’s Department of Physics and the Trottier Space Institute at McGill University. He is also the first author of the paper.

SMBHs are typically found at the centers of most galaxies. When two galaxies collide, their central SMBHs fall into orbit around each other. The gravitational pull from nearby stars slows them down as they revolve, causing them to spiral inward toward a merger. Previous models indicated that when SMBHs approached within roughly one parsec, their gravity would scatter dark matter particles away, halting their inward spiral.

However, Alonso-Álvarez and his co-authors, James Cline from McGill University and CERN, and Caitlyn Dewar, a graduate student at McGill, propose a new model. Their model suggests that dark matter particles interact with each other in a way that prevents them from being dispersed. This keeps the density of the dark matter halo high enough to continue interacting with the SMBHs, facilitating their merger.

The Importance of Dark Matter Interactions

“The possibility that dark matter particles interact with each other is an assumption we made, an extra ingredient that not all dark matter models contain,” says Alonso-Álvarez. “We argue that only models with that ingredient can solve the final parsec problem.”

This discovery has significant implications. The background hum of gravitational waves, detected by the Pulsar Timing Array, has wavelengths much longer than those first detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015. LIGO’s detection involved the merger of two black holes about 30 times the mass of the Sun. In contrast, the Pulsar Timing Array reveals gravitational waves by measuring minute variations in signals from pulsars, rapidly rotating neutron stars that emit intense radio pulses.

Understanding Dark Matter

The new findings also provide a window into the nature of dark matter. “Our work is a new way to help us understand the particle nature of dark matter,” says Alonso-Álvarez. “We found that the evolution of black hole orbits is very sensitive to the microphysics of dark matter, which means we can use observations of supermassive black hole mergers to understand these particles better.”

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The researchers discovered that the interactions between dark matter particles they modeled also explain the shapes of galactic dark matter halos. “The final parsec problem can only be solved if dark matter particles interact at a rate that can alter the distribution of dark matter on galactic scales,” Alonso-Álvarez notes. “This was unexpected since the physical scales at which the processes occur are three or more orders of magnitude apart. That’s exciting.”

This groundbreaking research sheds light on the long-standing final parsec problem and opens new avenues for understanding the enigmatic nature of dark matter. As scientists continue to unravel these cosmic mysteries, our comprehension of the universe and its most potent forces expands. Continue reading at Education Post News for more stories.