Black Hole Threatens to Consume Gas Nebula

A simulation of how the gas cloud may break apart as it approaches the black hole.

Credit: ESO/MPE/MARC SCHARTMANN

There is nothing stirs the imagination more than the awesome power of cosmic black holes.

Star-size black holes are powerful enough, but the super-massive black holes that lurk at the centers of most galaxies are millions of times more powerful.

When they swallow a star or a giant gas cloud, we call the resulting flare of energy a quasar, which can be visible halfway across the universe.

Now it’s about to happen right in our back yard. Back in 2011, astronomers spotted an interstellar gas cloud traveling towards the Milky Way’s own super-massive black hole, which is about the mass of four million Suns.

By the scientists’ calculations, the cloud will meet its doom in September or October 2013. “The impact will be deeper and more exciting than we thought,” says Stefan Gillessen, of the Max Planck Institute for Extraterrestrial Physics, in Garching, Germany, and the lead author of the Nature report that first announced the cloud’s existence.

Ordinarily, astronomers would expect an interstellar cloud like this (as well as any stars in the vicinity) to be orbiting the central black hole at an angle, spiraling in only gradually.

Not this one, though. “It’s remarkable how directly it’s moving toward the black hole,” says Reinhard Genzel, of the University of California, Berkeley, one of Gillessen’s co-authors. “Someone really aimed it very well.”

Astronomers have already seen changes in the cloud’s structure since it was first discovered. “There are clear signs that it’s being stretched,” says Gillesen.

That’s a result of tidal forces: the cloud’s leading edge feels the black hole’s gravity much more strongly than the trailing edge.

The difference in speed between front and rear is about 360 miles per second, and by April, says Gillesen, “we’re pretty sure the cloud should be starting to shred apart.” It is reminiscent, albeit on a much larger scale, of the fragmentation of Comet Shoemaker-Levy 9, which was tidally broken apart by Jupiter’s gravity before plunging to its death in July 1994.