Black Hole Simulation Breaks Ground

July 6, 2007 — Super-massive black holes at the centers of galaxies have just been promoted from the freak show to the big top. A new supercomputer simulation recreating the evolution of the universe is including, for the first time, the effects of the matter-eating monsters found at the heart of almost every galaxy.

Previous attempts to simulate how the universe evolved from an almost uniform expanse of matter and energy into our current cobweb of galactic clusters had not included the super-massive black holes.

One reason for the omission was that until a few years ago, it wasn't at all clear that black holes were important in the making of galaxies.

But that thinking has changed.

"You cannot forget black holes," said cosmologist Tiziana Di Matteo at Carnegie Mellon University. "What the simulations are trying to investigate is whether we understand the role black holes play."

Discoveries by astronomers make a strong case that all galaxies, at their centers, likely have black holes with masses equivalent to millions of Suns. They have also observed that the larger the galaxy, the larger the central black hole and the faster stars move in the galaxy — no matter how close they are to the center.

But even the largest black holes only comprise a thousandth of the mass and gravity of any given galaxy, Di Matteo told Discovery News.

"The two things form together," she said of galaxies and their central black holes. That's the only way to make sense of how they seem to "know" of each other without a strong gravitational connection.

That's not to say central super-massive black holes don't make themselves known in other ways. One thing they do with a lot more pizzazz than any star is convert matter into a huge amount of energy.

The incredible blast of energy from matter screaming into a super-massive black hole may do little to stars, but it can blast dust and gas out of a galaxy. And that, in turn, alters the entire appearance and future evolution of a galaxy, since without cold clouds of gas it's very hard for new stars to form.

"When material falls into these black holes, tens of percents of the matter can be released as energy," explained theoretical physicist Avi Loeb Harvard University at the Harvard-Smithsonian Center for Astrophysics. This is much more than the one percent or so of mass that is converted into energy inside stars by way of nuclear fusion — the engine that makes all stars shine.

Luckily for us in the Milky Way, the gas-blasting scream of doomed matter only happens when the monster is feeding, which is not the case for the two to four-million-solar-mass black hole at the center of our galaxy.

Just how this all fits into the making of the universe on a larger scale is exactly what Di Matteo and her colleagues are trying to discover with the simulation.

"It's putting things into a bigger context," said Loeb. A good human analogy, he says, is how sociologists put a family into a larger context to study all of society. Any given family may be small, but how they function has profound implications for society at large.

The same may go for super-massive black holes in the larger universe, he said.

To make the new simulation of the universe, called BH Cosmo, the researchers used all 2,000 processors of the Cray XT3 supercomputer and crunched equations for four weeks.

Di Matteo and her colleagues Jorg Colberg, Volker Springel, Debora Sijacki and Lars Hernquist will be publishing the results of their simulation in Astrophysical Journal.