Simulating chaotic interactions of three black holes

Dutch student Arend Moerman (Leiden University, the Netherlands) has defended his thesis research on the simulation of chaotic interactions of three black holes. The simulations, which he carried out together with researchers from Leiden and Oxford, show that lighter black holes tend to slingshot each other out into space, while heavier ones tend to merge. The research will be published in the leading journal Physical Review D.

Leiden master's student in astronomy Arend Moerman spent a year investigating the dynamic interactions and collisions between three imaginary black holes. The interactions between three bodies such as stars or planets or black holes cannot be predicted with an elegant formula. Moerman therefore used a computer that calculates what happens for a short period of time and then uses the result for the next period of time.

Extended with theory of relativity

The computer code is an extended version of the code used by first author Tjarda Boekholt (University of Oxford, United Kingdom) and co-author Simon Portegies Zwart (Leiden Observatory, Leiden University) in 2020 and 2018. The new, extended code takes Einstein's theory of relativity into account. This is important because the theory of relativity plays a major role especially in the case of heavy objects such as black holes.

The researchers varied the masses of the three interacting black holes. They started with one solar mass and went up to a billion times the mass of the sun.

Tipping point

Around ten million solar masses, there appeared to be a tipping point. In the simulations, black holes that are lighter than about ten million solar masses mostly eject each other through a gravitational slingshot. Black holes heavier than about ten million solar masses start to merge. First, two black holes merge. The third black hole will follow later. The black holes merge because they lose kinetic energy and that is because they emit gravitational waves.

"Arend's work", says Simon Portegies Zwart, "has led to a new understanding of how black holes become supermassive. In the simulations, we see that heavy black holes no longer endlessly move around each other, but that, if they are heavy enough, they collide pretty much instantly."

Moerman received the highest possible mark for his master's thesis. Meanwhile, he has started a second graduation research projec about DESHIMA, a Dutch-Japanese spectroscope on chip.

Reference: 

Tjarda C. N. Boekholt et al, Relativistic Pythagorean three-body problem, Physical Review D (2021). DOI: 10.1103/PhysRevD.104.083020