Black hole set to devour cloud of dust, gas

Last Updated: Tuesday, October 23, 2012 - 12:42

Washington: A black hole in the centre of our galaxy is getting ready to devour much of an approaching cloud of dust and gas known as G2.

A supercomputer simulation prepared by two Lab physicists and a former postdoc suggests that some of G2 will survive, although its surviving mass will be torn apart, leaving it with a different shape and questionable fate.

The findings are the work of computational physicist Peter Anninos and astrophysicist Stephen Murray, both of AX division within the Weapons and Complex Integration Directorate (WCI), along with their former postdoc Chris Fragile, now an associate professor at the College of Charleston in South Carolina, and his student, Julia Wilson.

They came up with six simulations, using the Cosmos++ computer code developed by Anninos and Fragile, which required more than 50,000 computing hours on 3,000 processors on the Palmetto supercomputer at Clemson University in Columbia, South Carolina.

Previous simulations of the upcoming event had been done in two-dimensions, but the Cosmos++ code includes 3D capability, as well as a unique “moving mesh” enhancement, allowing the simulation to more-efficiently follow the cloud’s progression toward the black hole.

The black hole is known as Sgr A*. “Sgr” is the abbreviation for Sagittarius, the constellation near the centre of the Milky Way. Most galaxies have a black hole at their centre, some thousands of times bigger than this one.

“While this one is 3-to-4 million times as big as our Sun, it has been relatively quiet. It’s not getting fed very much,” according to Murray.

The composition of the G2 cloud and its origin is still a mystery.

Astronomers originally noticed something in the region in 2002, but the first detailed determinations of its size and orbit came only this year. The dust in the cloud has been measured at about 550 degrees Kelvin, approximately twice as hot as the surface temperature on Earth. The gas, mostly hydrogen, is about 10,000 degrees Kelvin, or almost twice as hot as the surface of the Sun.

As the cloud approaches the black hole and begins to fall in to what Murray describes as “a gravity well” beginning next September, it will begin to shed energy, causing it to heat to incredibly high temperatures, visible to radio and X-ray telescopes on Earth as well as orbiting satellites such as NASA’s Chandra X-ray Observatory.

But it won’t be a collision course.

The point at which a stellar object can no longer escape being swallowed by a black hole is known as the Schwarzschild radius, a quantity whose value depends on the black hole’s mass, the speed of light and the gravitational constant.

The cloud will actually pass far enough away that it will escape the point of no return by approximately 2,200 Schwarzschild radii, which in this case is about 200 times as far as Earth is from the Sun.

But the supercomputer simulations show that the cloud will not survive the encounter.

The close encounter will take several months. The entire event is predicted to last less than a decade.

ANI



First Published: Tuesday, October 23, 2012 - 12:42

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