The final dance of unequal black hole partners

Solving common relativity equations is not an easy task to collide with black holes.

Physicists began using supercomputers back in the 1960s to solve such a difficult problem. In 2000, with no solutions in sight, Kip Thorne, one of the 2018 Nobel laureates and one of LIGO’s designers, famously believed that there would be an observation of gravitational waves before a statistical compromise could be reached.

In 2005, Carlos Lusto, then at the University of Texas at Brownsville, and his team at the Texas Advanced Computing Center created a solution using the Lonestar supercomputer, but lost that bet. (Together, the NASA and Celtic groups receive independent solutions.)

In 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) first observed such waves, Lusto was shocked.

“We realized two weeks ago that this was really out of nature and not from inputting our simulation as a test,” said Lou Lou Stowe, a professor of mathematics at the Rochester Institute of Technology (RIT). “The comparison with our simulations was so obvious. You can see with your own eyes that it was a merger of two black holes.”

Lusto is back with a new statistical relativity milestone, this time mimicking a black hole merging where the mass of a large black hole is 128 to 1 in the smallest – which is a scientific problem at the very limit of what is possible to calculate. Its secret weapon: the Frontera supercomputer at TACC, the eighth most powerful supercomputer in the world and the fastest at any university.

His research was published with collaborator James Haley, supported by the National Science Foundation (NSF) Physical Review Letters [journals.aps.org/prl/abstract/ … ysRevLett.125.191102] This week. It may take many decades for the results to be confirmed experimentally, but it nevertheless serves as a computational achievement that will help advance the field of astrophysics.

“Modeling a pair of black holes is a very computational demand because of the need to maintain accuracy over a wide range of grid resolutions,” said Pedro Maronetti, NSF’s program director of gravitational physics. “The RIT Group has emulated the world’s most advanced simulations in this area, and each of them takes us closer to understanding the observations that gravity-wave detectors will provide in the near future.”

Ligo is only capable of detecting gravitational waves caused by small and intermediate mass black holes of approximately the same size. It would take observatories 100 times more sensitive to find the type of merger modeled by Lusto and Haley. Their findings show that the gravitational waves caused by the 128: 1 merger will look like any observer on Earth, but also show the characteristics of the final merged black hole, including its final mass, spin and recoil velocity. This caused some surprises.

“The speed of these merged black holes could be much higher than previously known,” Lusto said. “They can travel at 2,000 kilometers per second. They come out of the galaxy and wander around the universe. This is another interesting prediction.”

The researchers calculated gravitational wavelengths – a signal that would be considered close to Earth – including their frequency, amplitude and luminosity. Comparing those values ​​with the predictions of existing scientific models Delo, their simulations were within 2 percent of the expected results.

Previously, the largest mass ratio ever solved with high-precision was eight times less extreme than Lusto’s simulation. The challenge of simulating a large mass ratio is that it needs to solve the dynamics of systems that interact on additional scales.

Like many field computer models, Lusto uses a method called adaptive mesh refinement to obtain specific models of interactive black hole dynamics. This includes placing black holes, the space between them and the remote observer (us) on the grid or mesh and fixing mesh areas with more details where necessary.

Lusto’s team approached the problem about a method he compared to Xeno’s first paradox. By halving and halving the mass ratio when adding internal grid refinement layers, they were able to move from a 32: 1 black hole mass ratio to a 128: 1 binary system that goes through 13 orbits before the merger. On the frontera, it requires a continuous count of seven months.

“Frontera was a perfect tool for the job,” Lusto said. “Our problem requires high-performance processors, communications, and memory, and Frontera has all three.”

Simulation is not the end of the road. Black holes can have different spins and alignments, which affect the amplitude and frequency of the gravitational waves generated by their merger. Lusto will want to solve the equations 11 more times to get a good first series of possible “templates” to compare with future investigations.

The results will help designers of future earth- and space-based gravity wave detectors plan their devices. These include the state-of-the-art, third-generation ground-based gravitational wave detector and laser interferometer space antenna (LISA), which is slated to launch in the mid-2030s.

Research can also help to answer the basic secrets about black holes, such as how some people can grow millions of times out of the sun’s mass.

“Supercomputers help us to answer these questions,” Lusto said. “And the problems inspire new research and torch students’ future careers.”