Scientists have identified a new link between dark matter particles and supermassive black holes (SMBHs) that could solve the longstanding “final parsec problem” in astronomy.
The study, published in Physical Review Letters, reveals that dark matter particles play a crucial role in facilitating the merger of SMBH pairs. Previously, dark matter’s influence on these cosmic giants had been underestimated.
In 2023, astrophysicists detected a persistent “hum” of gravitational waves across the universe, believed to originate from numerous merging SMBH pairs, each billions of times more massive than the Sun. Theoretical simulations had shown that SMBH pairs tend to stall when they are about a parsec (three light years) apart, preventing further merger.
Gonzalo Alonso-Álvarez, a postdoctoral fellow at the University of Toronto and a co-author of the study, explained, “We show that incorporating the previously overlooked effects of dark matter can enable supermassive black holes to overcome this final parsec of separation and merge.”
The research team, led by Professor James Cline from McGill University, developed a new model demonstrating that interactions between dark matter particles do not cause dispersion. Instead, the density of dark matter in its halo allows SMBHs to spiral inward and merge.
According to the study, SMBHs are typically located at the centers of galaxies. When galaxies collide, their SMBHs enter close orbit. The gravitational influence of nearby stars initially slows their inward spiral, but the interaction with dark matter helps them eventually coalesce.
Alonso-Álvarez added, “The assumption that dark matter particles interact with each other is a key component that not all dark matter models include. We argue that only models with this feature can address the final parsec problem effectively.”
