Just a few years ago they said it couldn't be done, but now astrophysicists have succeeded in simulating the most extreme collision of two black holes yet: one black hole a hundred times more massive than the other. The accomplishment comes after simulations had pushed from one-to-one mass collisions five years ago all the way up to ten to one mass mergers.
"When two black holes collide in realistic astrophysical scenarios, they don't have the same size," said Carlos Lousto of the Rochester Institute of Technology's (RIT) Center for Computational Relativity and Gravitation.
Colliding galaxies would be the sort of scenario in which black holes of very different masses -- everything from two-to-one up to a million-to-one -- would fall into each other as they leak massive amounts of orbital energy by emitting gravitational waves.
Until now simulations had succeeded reproducing black hole collisions up to a 10-to-one mass ratio and reached the limits of those techniques, said Lousto. Going further seemed like something that would take five to 10 years to solve. But that was before researchers met in Canada last summer and came up with some new techniques.
"In a few months we came up with a solution," Lousto told Discovery News. "We think we can go beyond this mass ratio, maybe to a thousand-to-one."
"This is such a complex problem," said Lousto. "It had to be solved by supercomputers. We needed really large resources."
In fact, it took the 70,000-processor supercomputer at the Texas Advanced Computing Center nearly three months to complete the simulation.
The new simulation is especially important because it bridges a gap in two very different research approaches: one that started from similar mass black holes and another approach using what's called perturbation techniques that approximated thousand-to-one collisions, explained Yosef Zlochower, also of RIT. A paper announcing Lousto and Zlochower's findings has been submitted for publication in the journal Physical Review Letters.
The simulation can also help predict the signatures of gravitational waves that come from different mass ratio black hole collisions. That ought to make it easier for other astronomers now looking for gravitational waves to understand what exactly they are detecting.
"In order to detect them you have to understand what you are looking for," said astrophysicist Duncan Brown of Syracuse University's Gravitational Wave Group.
There are currently two large U.S. efforts underway to detect gravitational waves: the Laser Interferometer Gravitational Wave Observatory (LIGO), which is ground-based and the Laser Interferometer Space Antenna (LISA), which is a NASA-backed space borne gravitational wave observatory which is not yet off the ground.
This new simulation will help to develop gravitational wave-form families that gravitational wave astronomers can look for once their observatories succeed in detecting gravity waves, which Brown expects will be within the next five years.
"The goal of LISA is to do high precision tests of General Relativity," said Brown. "This has some major astrophysical implications."