Physicists at NASA Goddard Space Flight Center successfully simulated the merger of two massive, orbiting black holes – an achievement that has eluded physicists for decades.

Relying on Columbia, NASA’s record-setting supercomputer built from 20 SGI Altix systems, the Goddard team was able to simulate how colliding black holes will throw off gravitational waves that ripple throughout the fabric of the universe.

Variations on 24 equations based on Einstein’s relativity theory helped create the simulation of colliding black holes with equal mass – an event whose effects can continue for years. The black hole calculation stands out as the largest astrophysical “single run” ever performed on a NASA computer – the equivalent of 18 years of CPU time devoted to a single problem.

“These mergers are by far the most powerful events occurring in the universe, with each one generating more energy than all of the stars in the universe combined,” said Joan Centrella, head of the Gravitational Astrophysics Laboratory at Goddard. “By combining our latest codes with the tremendous computing power of Columbia, we now have realistic simulations that will help guide gravitational wave detectors coming online.”

To run the simulations on Columbia, Goddard physicists developed sophisticated software called Hahndol. The team scaled its code across up to 2,032 processors on Columbia – one-fifth of the massive system’s total processor count. By linking four, 512-processor Altix systems via the high-speed SGI NUMAlink interconnect, NASA enabled the scientists to access all of the processors’ memory at once. The project, begun some 18 months ago, has required millions of CPU hours. Individual calculations involved hundreds of Gigabytes of information.

According to John Baker, NASA astrophysicist and one of the project leaders at NASA Goddard, calculating some of Einstein’s more involved equations had proven elusive because representing the three-dimensional fabric of the universe is enormously complex, and simulating its behaviors grows increasingly complicated.

“You can picture the simulation taking place on a kind of 3D graph paper with hundreds of points, and we’ll calculate 80 variables for each point,” said Baker. “If the coordinates aren’t accurate, things go awry very quickly.”

NASA pursued the simulations because gravitational waves are notoriously difficult to detect and measure. By successfully simulating the waves, the Goddard researchers are assisting another NASA project: the Laser Interferometer Space Antenna (LISA). Made up of three spacecraft flying just more than 3 million miles apart in an equilateral triangle, the LISA project will carry extraordinarily precise instruments to detect if a gravitational wave passes between them. The sensitive instruments will recognize even the slightest force caused by a passing wave. For instance, if the laser that connects two LISA spacecraft is nudged as little as the width of an atom, the system will detect it.

The long-term project should help NASA scientists learn more about how black holes merge and how dying stars are consumed by black holes.

In the simulation, the black holes are roughly 4 million times the mass of the sun. An animation of the simulation was created by Chris Henze, senior research scientist at NASA Advanced Supercomputing Division. The 29-second animation of circling black holes illustrates the final stage of a rapidly accelerating process. Though the entire merger process occurs over hundreds of millions of years, the last stage is over in only minutes.