Scientists: Three Black Holes Can Merge
Three arrows indicate the positions of three quasars in this false-color composite taken by instruments at the Keck Observatory and Very Large Telescope.
Credit: S. G. Djorgovski et al., Caltech and EPFL.

If you thought one black hole was scary, be very afraid, because triple black-hole mergers are a real possibility in the universe, according to a new supercomputer calculation.

Astrophysicists used a computer model to predict what would happen if several black holes were to orbit each other. Often the trio would merge into one giant black hole.

"In our simulations we see three possibilities," said Carlos Lousto of the Rochester Institute of Technology's Center for Computational Relativity and Gravitation, who built the model with colleagues Manuela Campanelli and Yosef Zlochower. "They can mesh together into one big black hole, or two can mesh while the third orbits around in a very elliptical orbit. And a third possibility is that all three fly apart."

Though it sounds bizarre, a triple black hole merger isn't so far-fetched.

"Interestingly enough, at the beginning of last year, astronomers found the first triple quasar in the sky," Lousto told "That could be the first observed supermassive black hole triplet."

Quasars are extremely bright, faraway objects that scientists think are powered by giant black holes at the cores of galaxies. A team led by Caltech astronomer George Djorgovski used the W.M. Keck Observatory on Mauna Kea, Hawaii, to observe a system of three quasars about 10.5 billion light-years from Earth.

Lousto said this trio would probably collide eventually, though they are far enough apart it would likely take longer than the current age of the universe.

The merger of three black holes would be one of the most energetic events in the universe, releasing tons of energy in the form of gravitational waves, or warps in space-time.

So far, scientists have been unable to detect gravitational waves, which are predicted by Einstein's General Relativity. Physicists hope that may change soon when the first sets of data are analyzed from the ground-based detector known as the Laser Interferometer Gravitational Wave Observatory (LIGO) and the future NASA/European Space Agency space mission Laser Interferometer Space Antenna (LISA).

"We really hope we can detect gravitational waves," Lousto said. "That?s why our simulations are important. We need a model to predict what we would see. It tells the people who do those experiments what kind of signature is characteristic of black holes."

The scientists' model simulates the simplest case of a black hole triplet: three non-spinning black holes of equal masses. They plan to expand their models to include more complex systems.

Even their basic models were very computationally expensive and took their giant supercomputer two weeks, running 24 hours a day, to complete.

The researchers will detail their findings in the May issue of the journal Physical Review D. The team is also set to present their simulations at the annual meeting of the American Physical Society in St. Louis on April 14.