Astrophysicists Make Groundbreaking Discovery Linking Supermassive Black Holes and Dark Matter

The intricate relationship between supermassive black holes (SMBHs) and dark matter particles has been unraveled by astrophysicists, shedding light on the long-standing mystery known as the "final parsec problem." This new revelation stems from researchers' computations that uncovered an overlooked behavior of dark matter particles, presenting a potential solution to this astronomical quandary.

The findings, published in a recent article titled "Self-interacting dark matter solves the final parsec problem of supermassive black hole mergers" within Physical Review Letters, show the connection between pairs of supermassive black holes merging into a single, larger black hole. Prior to this discovery, theoretical simulations had demonstrated that when two mammoth celestial bodies came approximately a parsec apart (roughly three light-years), their progression towards merging halted.

The "final parsec problem" not only contradicted the theory that merging SMBHs constituted the primary source of the pervasive gravitational wave background, but it also challenged the notion that SMBHs grew from the merger of less massive black holes. However, the researchers involved in this study suggest that including the influence of dark matter can enable supermassive black holes to overcome this final separation, allowing them to merge successfully.

"Our calculations explain how that can occur, in contrast to what was previously thought," says Gonzalo Alonso-Álvarez, a co-author of the paper and postdoctoral fellow at the University of Toronto and the Trottier Space Institute at McGill University. The team, including co-authors Professor James Cline from McGill University and Caitlyn Dewar, a master's student in physics at McGill, placed significance on the previously overlooked effect of dark matter in revealing this phenomenon.

A prevalent belief posits that SMBHs reside at the cores of most galaxies, and when two galaxies collide, their respective SMBHs find themselves in mutual orbit. Within this dance of immense gravity, the surrounding stars' tug slows down the SMBHs' movements, causing them to spiral inwards until they inevitably merge. Earlier theories stipulated that the SMBHs' interaction with the dark matter cloud or halo in which they are immersed became noticeable when the separation amounted to around a parsec. These theories suggested that the gravity exerted by the spiraling SMBHs expelled dark matter particles from the system, resulting in a scarcity of dark matter and the cessation of orbit reduction.

Contradicting these established models, Alonso-Álvarez and the team proposed a new model in which dark matter particles interact with one another, ensuring their cohesion rather than dispersion. Consequently, the density of the dark matter halo remains high enough for continued interactions with the SMBHs, thereby degrading their orbits and facilitating the merger. "Only models with that ingredient can solve the final parsec problem," notes Alonso-Álvarez.

The ripple effects of these colossal cosmic collisions manifest as gravitational waves, distinct from those initial waves detected by LIGO in 2015 and originating from the merger of two black holes. The gravitational waves composing this background hum observed by the Pulsar Timing Array possess longer wavelengths, requiring minute variations in signals from pulsars to unveil their existence.

Cline emphasizes, "A prediction of our proposal is that the spectrum of gravitational waves observed by pulsar timing arrays should be softened at low frequencies. The current data already hint at this behavior, and new data may be able to confirm it soon."

Aside from elucidating SBMH mergers and grasping the gravitational wave background signal, this breakthrough follows a path that leads to a deeper comprehension of dark matter. Alonso-Álvarez states, "Our work is a new way to help us understand the particle nature of dark matter." The researchers' model offers an explanation for the shapes of galactic dark matter halos, as interactions between the dark matter particles can alter their distribution on such large scales.

The revelation of the connection between supermassive black holes and dark matter particles not only resolves the final parsec problem but also provides valuable insight into the nature of dark matter itself. The cross-disciplinary exploration of these cosmic phenomena allows for a comprehensive understanding of the universe and the intricate web woven within its very fabric.

Earlier, SSP wrote about an ancient black hole dance with colliding galaxies that could be seen with James Webb Space Telescope.