A team led by Rochester Institute of Technology (RIT) has simulated two supermassive black holes in the final stage before they collide. The model predicts the light signals that the gas around them should give off. The work appeared in The Astrophysical Journal Letters, and RIT announced it on February 14, 2018.
Supermassive black holes sit at the centers of galaxies. They are fed by doughnut-shaped disks of gas. When two of them spiral toward each other, their gravity heats the gas and disrupts its flow. As a result, the system should send out periodic signals, from visible light up to X-rays.
This is the first simulation in which a large gas disk around a black hole pair feeds a separate mini-disk around each black hole. To get there, the team combined general relativity with magnetohydrodynamics.
A filling and refilling cycle
The model showed something new. The big outer disk feeds one mini-disk more than the other, so gas keeps filling and draining from each of them. Lead author Dennis Bowen, a postdoctoral researcher at RIT, said this cycle shapes the light signatures. He added that no one has yet observed two supermassive black holes this close together.
Co-author Manuela Campanelli said the simulated evolution runs long enough to show what real observations might look like. She also leads the NSF-funded project behind the study.
The research supports multimessenger astrophysics, which combines light and gravitational waves to study the same event. Pairs of supermassive black holes emit gravitational waves at lower frequencies than smaller black holes do. That is why LIGO, which first detected waves from stellar-mass black hole mergers in 2016, cannot pick them up. Instead, scientists expect the space-based LISA detector to do so in the 2030s.
On the light side, the LSST telescope was being built on Cerro Pachón in Chile. Once it starts work in the 2020s, it should produce the widest and deepest survey of light from the sky.
The simulations ran on computers at RIT’s Black Hole Lab and on the Blue Waters supercomputer at the University of Illinois at Urbana-Champaign. Other authors are Scott Noble of NASA Goddard Space Flight Center, Vassilios Mewes of RIT, Miguel Zilhão of the Universidade de Lisboa and Julian Krolik of Johns Hopkins University. A follow-up paper will look at how gas flowing in and out of the disks lines up with the changing light.
