By Andrew Grant
An ill-fated gas cloud has begun a close encounter with the monstrous black hole at the center of the Milky Way, a fresh set of observations reveals. Astronomers don’t expect the cloud to emerge intact, resulting in an unprecedented view of our galaxy’s largest black hole feasting on its prey.
In December 2011, astronomers identified the gas cloud, called G2, and found that its orbit would bring it perilously close to the Milky Way’s central black hole by mid-2013. Nineteen months ago, the immense gravity of the black hole, which weighs in at about 4.3 million times the mass of the sun, was already squeezing and stretching the gas cloud as if it were pasta dough.
Now images captured in April with the Very Large Telescope in Chile show that the leading edge of G2 has whipped around the black hole’s far side. “The line of sight is such that the gas cloud is falling away from us toward the black hole,” says Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. “Some material swung by the back side of the black hole and is now flying toward us.”
“If you think of the cloud as a roller coaster train, the first carriage has already swung by the black hole,” Gillessen says. “The main part of the train is still in approach.”
The gas cloud is whizzing through space at up to 3,000 kilometers per second, 100 times the speed at which Earth orbits the sun and a whopping 1 percent of the speed of light. In just a few months, the black hole has not only accelerated the cloud to those speeds, but reversed the motion of the front side a full 180 degrees. The findings will appear in an upcoming Astrophysical Journal.
Gillessen and his team also found that the black hole has stretched G2 to twice its length last year. As a result, the researchers predict that the bulk of the cloud won’t make its closest approach to the black hole until early next year. When that happens, telescopes around the world will point at the galactic center to capture the drama.
Dimitrios Giannios, an astrophysicist at Purdue University in West Lafayette, Ind., does not expect G2 to survive its encounter with the galaxy’s central black hole. The cloud will probably fade from view in coming months as it continues to stretch out, he says. But its remnants might gradually get funneled into the black hole within a few decades, culminating in a rare bright display as they approach the point of no return. “It would be a last echo of the death of this cloud,” he says.
