FEATURE
Finding the Holy Grail
Goddard Scientists Discover What Happens When Black Holes Merge
A team of Goddard scientists has found the “holy grail” of numerical relativity by simulating what would happen if two massive black holes merged in a cataclysmic collision, which scientists describe as second only to the Big Bang as one of nature’s most powerful and energetic events.
Using sophisticated numerical codes, the team has calculated the shape of the resulting gravitational waves that would radiate in all directions, much like the ripples that happen when a stone is thrown into a pond. Although Einstein predicted the existence of gravitational waves in his Theory of General Relativity, no one has directly detected them yet. And until now, no one has calculated what these waves might look like in a science called numerical relativity, said Joan Centrella, Chief of the Gravitational Astrophysics Laboratory and principal investigator on the study.
Now that Centrella and her team have demonstrated the waveforms, scientists have the means to test Einstein’s theories under extreme gravitational fields. This will especially benefit NASA’s proposed Laser Interferometer Space Antenna (LISA), a gravitational wave detector that the Agency hopes to fly the next decade (see related story). Rather than simply inferring the existence of gravitational waves due to the motion of celestial bodies, LISA will use advanced laser interferometry to directly detect and measure them.
Fundamentally New Knowledge
“Our results will allow LISA to carry out tests of Einstein’s general relativity in a regime that’s never been accessible before,” Centrella said. “The waveforms we have produced give us the first look at what happens when black holes merge. This will give us fundamentally new knowledge about one of the most amazing theories ever conceived by the human mind.”
Although Einstein proposed his theories 90 years ago, no one has ever solved the underlying equations with paper and pen due to their great complexity. “The only way to solve these equations is on a computer using the methods of numerical relativity, but this has proven difficult. In fact, a few years ago, some even said that numerical relativity was impossible because the computer codes were unstable. They crashed well before the black holes completed even a fraction of an orbit,” said Centrella, who used Internal Research and Development funding to begin the work at Goddard. |
This image shows the two massive black holes just before they merge. It was based on calculations performed by Goddard numerical relativist Joan Centrella and her team. Photo Credit: Chris Henze, Ames Research Center
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More Work Remains
“Although her team’s work represents a major breakthrough, she concedes that more work still needs to be done. Relying now on Goddard’s Core Capabilities funding, a Beyond Einstein Foundation Science grant from NASA Headquarters, and the LISA project, she and her team are focusing on even more complex calculations related to black-hole mergers. Originally, her calculations focused on black holes with equal masses and no spin. However, in nature black holes do spin, and binary black holes are likely to have non-equal masses. “So, there is some real work yet to do. But our recent work opens the way for this to happen.”
Revealing Mass and Motion
Much can be learned from gravitational waves, which occur when massive celestial objects move and disrupt the fabric of space-time that surround them, Centrella said.
Similar to visible light in that they both travel in waves, spreading outward from their sources, gravitational waves carry information directly about the mass and motion of the objects that created them. “In particular, the gravitational waveform provides a map of what the black holes are doing when they move through spacetime,” she added. “Even though we can’t see the black holes, which are deep inside the centers of galaxies, we can map their motions by observing their gravitational waveforms.” |
Using sophisticated computer codes, Goddard’s numerical relativists calculated the gravitational waves that would radiate out in all directions when two massive black holes merged. Photo Credit: Chris Henze, Ames Research Center
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Much of what scientists know about gravity comes from experiments within the solar system, where the gravitational fields are relatively weak. These experiments confirm Einstein’s basic premise that gravity is a universal force connecting all forms of mass and energy. This means that gravity should act the same throughout the universe; however, important questions remain unanswered — particularly in the area of how gravity behaves under extreme conditions, such as when black holes merge.
Centrella and her team recently submitted their findings for publication in The Physical Review, a scientific journal.
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