The first gravitational waves, initially predicted by Albert Einstein in 1916, were detected from Earth in 2015.

New research, in the wake of the gravitational wave discoveries, sheds light on the environments that could lead to black hole merger events. The work is being presented this week at the 2023 National Astronomy Meeting by Ph.D. Oxford University student Connar Rowan.

The first gravitational waves, initially predicted by Albert Einstein in 1916, were detected from Earth in 2015. However, determining their origin in the cosmos has been unknown. To be detectable over such vast distances, the gravitational waves we observe can only come from very close pairs of large, highly dense objects, such as black holes or neutron binary stars. There have now been more than 90 such detections, though the primary astrophysical environment that allows these objects to come close enough to emit gravitational waves remains a mystery.

One possible environment in which black holes can undergo frequent mergers is in quasars. A quasar is a powerful active galactic nucleus fueled by a supermassive black hole. A dense disk of gas revolves around a supermassive black hole at close to the speed of light, resulting in extremely bright emissions.

The interactions of stellar-mass black holes with the gas disk of a supermassive black hole are very complex and require sophisticated computer simulations to understand. In the new research, the team of astronomers from the University of Oxford and Columbia University examined the behavior of such stellar-mass black holes embedded in the disk. The work suggests that stellar-mass black holes could be pulled into dense disks of quasar gas and forced into binary systems by gravitational interactions with each other and with the gas in the disks.

The team has performed high-resolution simulations of the gaseous disk of a quasar containing two stellar-mass black holes. The goal of the simulation is to see if black holes are captured in a gravitationally bound binary system and possibly merge at a later time within the gas disk. These simulations use 25 million gas particles to mimic the complex gas flows during the encounter, requiring a computational run time of around three months for each simulation.

Simulations show that gas slows black holes down during the encounter, so black holes that would normally just fly apart remain gravitationally bound, trapped in orbit around each other as they both orbit the supermassive black hole. This occurs through a mix of gravitational tugs on each other and the massive streams of gas in the disk and the individual “mini” disks around the individual black holes.

In addition, direct gas drag, analogous to air resistance, also plays a role when gas “eaten” by black holes along their path forces them to slow down. In response to the absorption of the black hole’s kinetic energy through the gravitational interaction, gas is violently ejected immediately after the encounter. This result occurs in most simulations and confirms previous expectations that the gas greatly facilitates the capture of black holes in bonded pairs.

The direction of the black holes’ orbit was also found to affect how they evolved. In half retrograde binary systems (binary systems where black holes orbit each other in the opposite direction of their orbit around the supermassive black hole), the black holes could get close enough to produce significant gravitational waves and dissipate their energy very quickly. orbital through these waves. emissions, merging very abruptly.

The direction of the black holes’ orbit was also found to affect how they evolved. In half retrograde binary systems (binary systems where black holes orbit each other in the opposite direction of their orbit around the supermassive black hole), the black holes could get close enough to produce significant gravitational waves and dissipate their energy very quickly. Orbital through these waves. emissions, merging very abruptly.

source,:https://nam2023.org/