SCIENCE

Telescopes can see light from distant galaxies; but it takes a supercomputer to see why the centre of our own is so dark.

The intense gravity near black holes makes for a violent, active region of space. Gas or stars that wander too near are torn apart, their energy released as X-rays. In the centre of the Milky Way, 26,000 light years away, is a black hole over four million times heavier than our Sun, but only modestly brighter.  It's eerily quiet -- too quiet.

This mystery may have been solved by an international team of scientists lead by researchers at the Canadian Institute of Theoretical Astrophysics, and the University of Toronto Department of Astronomy and Astrophysics, in work published in the current issue of Monthly Notices of the Royal Astronomical Society. The team used supercomputers at SciNet, University of Toronto, to carry out the largest computer simulations ever performed in Canada so they could test out their new theory.

"We've long thought that magnetic fields can choke off the flow of material into the black hole" says Prof. Ue-Li Pen of CITA. "Our earlier work suggested this, but then, it just wasn't possible for a simulation to look at the huge range of lengths - from light years to light minutes - needed to track the hot gas as it falls all the way towards the black hole."

"But our new methods, and SciNet, let us do just that," added Dr. Bijia Pang. "We broke up the region of space near the black hole into 100 billion zones, and spread them over almost 18 thousands processors on SciNet's largest cluster. This finally gave us the resolution we needed to test our model - we could see, with unprecedented accuracy, the fields halting the turbulence and keeping the gas from falling in."