Solving the equations of general relativity for colliding black holes is not a simple problem.
Physicists began using supercomputers to work out a solution to this famously difficult problem in the 1960s. In 2000, there was no solution in sight, Kip Thorne, 2018 Nobel Prize winner. and is one of the designers of LIGO, famously betting that there will be an observation of gravitational waves before reaching a digital solution.
He lost that bet, in 2005, Carlos Lousto, then at the University of Texas at Brownsville, and his team created a solution using the Lonestar supercomputer at the Computer Center. Advanced Texas. (At the same time, the teams at NASA and Caltech came up with independent solutions.)
In 2015, when the Laser Interferometer Gravitational Wave Observatory (LIGO) first observed such waves, Lousto was shocked.
“It took us two weeks to realize this actually came from nature, not from importing our simulation like,” said Lousto, now professor of mathematics at the Rochester Institute of Technology (RIT). a test. “The comparison with our simulation is so obvious. You can see with the naked eye that it’s a fusion of two black holes.”
Lousto is back again with a new relativity milestone, this time simulating black hole fusion where the mass ratio of a larger black hole to a smaller one is 128 to 1 – a problem. science is at a very high computational limit. His secret weapon: the Frontera supercomputer at TACC, the eighth most powerful supercomputer in the world and the fastest of any university.
His research with collaborator James Healy, supported by the National Science Foundation (NSF), has been published in Letter of physical assessment [journals.aps.org/prl/abstract/ … ysRevLett.125.191102] this week. It may take decades to confirm the results experimentally, but nonetheless it is still a computational achievement that helped propel the field of astrophysics forward.
“Modeling black hole pairs of very different masses requires a lot of computation because it is necessary to maintain accuracy at a wide range of resolutions,” said Pedro Marronetti, director of the physics of gravity program at NSF. grid prize “. “The RIT team has done the most advanced simulations in the world in the field, and each of them will bring us closer to the observations that gravitational wave detectors will provide in the future.” near the.”
LIGO can only detect gravitational waves caused by intermediate and small mass black holes of approximately equal size. Observatories would need 100 times more sensitivity to detect the type of merger that Lousto and Healy emulated. Their findings not only show what gravitational waves caused by a 128: 1 fusion will look like to an observer on Earth, but also the characteristics of how the last fused black hole will be. its final weight, rotation speed and recoil. This led to some surprises.
“These fused black holes could have a much greater rate than previously known,” Lousto said. “They can travel at speeds of 5,000 kilometers per second. They fly out of a galaxy and roam through space. That’s another interesting prediction.”
The researchers also calculate gravitational waveforms – signals that will be detected near Earth – for such fusions, including their maximum frequency, amplitude, and luminosity. Comparing those values with predictions from existing scientific models, their simulations are within 2% of the expected results.
Previously, the largest mass ratio ever solved with high precision was 16 to 1 – eight times less extreme than Lousto’s simulation. The challenge of simulating larger mass ratios is that it requires solving the dynamics of interactive systems at complementary scales.
Like computer models in many disciplines, Lousto uses a method called adaptive mesh refinement to obtain accurate models of the dynamics of interactive black holes. It involves placing black holes, the space between them and the distant observer (us) on a grid or grid, and refining areas of the mesh with greater detail where needed.
Lousto’s group approached the problem with a method he compared with Zeno’s first paradox. By halving and halving the mass ratio while adding levels of refinement of the internal mesh, they can go from a 32: 1 black hole mass ratio to a 128: 1 undergone binary system. 13 orbits before fusion. On Frontera, it required seven consecutive months of computation.
“Frontera is the perfect tool for the job,” Lousto said. “Our problem requires high performance processor, communication, and memory, and Frontera has all three.”
Simulation is not the end of the road. Black holes can have many different spins and configurations, affecting the amplitude and frequency of the gravitational waves their fusion produces. Lousto wants to solve the equations 11 more times to get the best possible first set of “patterns” to compare with future findings.
The results will help future Earth and space gravitational detector designers plan their devices. These include the advanced, third-generation ground-based gravitational wave detector and the Laser Interferometer Space Antenna (LISA), targeted for launch in the mid-2030s.
Research may also help solve fundamental mysteries about black holes, such as how a number can grow so large – millions of times the mass of the Sun.
“The supercomputer helps us answer these questions,” Lousto said. “And problems inspire new research and pass the torch on to the next generation of students.”
Researchers reveal the origins of black hole fusion
Carlos O. Lousto et al., Exploring small mass fraction binary black hole fusion through Zeno’s binary approach, Letter of physical assessment (Year 2020). DOI: 10.1103 / PhysRevLett.125.191102
Provided by the University of Texas at Austin
Quote: Black hole partners’ final dance unequal (2020, November 6) accessed November 7, 2020 from https://phys.org/news/2020-11-unequal-black- hole-partners.html
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