Astrophysicists uncover supermassive black hole/dark matter connection in solving the ‘final parsec problem’

Researchers have discovered a connection between some of the largest and smallest objects in the universe: supermassive black holes and dark matter particles.

According to their new calculations, Supermassive black hole (SMBH) has been overlooked until now Dark matter particlesHe proposed a solution to astronomy’s long-standing “last parsec problem.”

The research is described as “Self-interacting dark matter solves the last parsec problem of supermassive black hole mergers.” Published This month’s journal Physics Review Letter.

In 2023, astrophysicists announced they had detected a “hum” of gravitational waves permeating the universe. They hypothesized that this background signal emanated from millions of merging pairs of SMBHs, each with billions of times the mass of the Sun.

But theoretical simulations have shown that if these massive objects were to spiral together, their approach would stop when they were about one parsec apart (around three parsecs). Light years—This means merger.

This “final parsec problem” not only contradicted the theory that merging SMBHs are the source of the gravitational wave background, but also the theory that SMBHs grow by merging with less massive black holes.

“When we take into account the previously overlooked influence of dark matter, we find that supermassive black holes can help survive this final parsec separation and merger,” said study co-author Gonzalo Alonso-Alvarez, a postdoctoral researcher in the Department of Physics at the University of Toronto, the Department of Physics at McGill University and the Trottier Institute for Space Studies. “Our calculations explain how this could happen, in contrast to what was previously thought.”

Co-authors of the paper include James Klein, professor of theoretical physics at McGill University in Switzerland and CERN, and Caitlin Dewar, a Master of Science student in Physics at McGill.

SMBHs are thought to be located at the centers of most galaxies, and when two galaxies collide, the SMBHs orbit each other. As the SMBHs orbit each other, they are pulled by the gravity of nearby stars, slowing them down. As a result, the SMBHs spiral inward toward the merger.

Previous merger models had shown that when SMBHs get closer than about a parsec, they begin to interact with the dark matter cloud, or halo, they are embedded in. The models showed that the gravity of the spiraling SMBHs would expel dark matter particles from the system, resulting in dark matter becoming so sparse that no energy is drawn from the pair and they no longer contract in their mutual orbits.

These models denied any effect of dark matter on the orbits of SMBHs, but the new model by Alonso-Alvarez and his colleagues reveals that the dark matter particles interact in such a way that they don’t disperse: the density of the dark matter haloes remains high enough that interactions between the particles and the SMBHs would continue to degrade the SMBHs’ orbits, paving the way for them to merge.

“The possibility of dark matter particles interacting is an assumption that we make, an additional ingredient that is not included in all dark matter models,” Alonso-Alvarez says, “and our argument is that only models that have that ingredient can solve the final parsec problem.”

The background noise produced by these gigantic cosmic collisions consists of gravitational waves with much longer wavelengths than those first detected by astrophysicists operating the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015. These gravitational waves were produced by the merger of two black holes, both with masses about 30 times that of the Sun.

This background noise has been detected in recent years by scientists operating Pulsar Timing Arrays, which reveal gravitational waves by measuring tiny changes in signals from pulsars, fast-spinning neutron stars that emit powerful pulses of radio waves.

“The prediction of our proposal is Gravitational waves “The oscillations observed by the Pulsar Timing Array should be damped out at low frequencies,” Klein said. “Current data already suggest this phenomenon, and new data may confirm it in the next few years.”

The new results not only provide insight into SBMH mergers and the gravitational wave background signal, but also offer a window into understanding the nature of dark matter.

“Our work is a new way to understand the particle nature of dark matter,” Alonso-Alvarez said. “We found that the orbital evolution of black holes is very sensitive to the microphysics of dark matter, which means that we can use observations of supermassive black hole mergers to better understand these particles.”

For example, the researchers found that the interactions between dark matter particles they modeled could also explain the shape of galaxies’ dark matter halos.

“We now know that the final parsec problem can only be solved if dark matter particles interact with each other at speeds that are able to change the distribution of dark matter on the scale of galaxies,” Alonso-Alvarez says. “This was unexpected, because the physical scales at which the processes occur are more than three orders of magnitude apart. This is very exciting.”