University astronomers watch as black hole swallows gas cloud


A little more than 26,000 years ago, a gaseous object collided with a giant black hole in the center of the Milky Way. Now, astronomers will finally have an opportunity to witness it.

The cloud, which has been named G2, is predicted to collide with Sagittarius A, a black hole located 26,000 light years away near the middle of the galaxy, at some point in the next two months. According to physics doctoral student Patrick Crumley, the event will be one of the first of its kind that scientists have been able to predict in advance.

G2, three times the size of the Earth, appears microscopic in the face of Sagittarius A, which is 4 million times bigger than the sun.

Crumley said the collision will allow astronomers to verify predictions that have been made about the interactions between black holes and objects like G2.

“The black hole at the center of our galaxy is not very efficient,” Crumley said. “It doesn’t eat the gas around it very quickly, so we might actually get to see a piece of gas fall onto the black hole and turn it on. We would see it either spit it out or eat it or do some crazy stuff like that.”

According to physics and astronomy senior John Pelletier, G2 won’t be pulled in all at once. Pelletier said the colder G2 is, the slower it will be absorbed.

“Even though it’s going to start colliding, it could take up to a year for the gas cloud to have spiraled close enough to the black hole to get hot enough to emit the radiation we’re hoping for,” Pelletier said. 

Pelletier will be observing the process as it continues to happen.

“The event is exciting for me,” Pelletier said. “It will give us a front row seat to see how our black hole consumes matter. I also want to try observing it with a remote radio telescope also [through the National Radio Astronomy Observatory]. It’s a great transient event in astronomy, and these things always excite me.”

Astronomy professor John Lacy said he is unsure of whether there will be any direct observations made at the UT’s McDonald Observatory in West Texas because of the limitation on the types of wavelengths that are detectable by the technology there.

“The observations I know of [on G2] are at infrared and radio wavelengths, and the infrared observations [necessary] are using adaptive optics [a technique for getting very high resolution on the sky], which we don’t do at McDonald,” Lacy said.

The collision will be studied at the Very Large Array Observatory in New Mexico and Mauna Kea Observatory in Hawaii. According to astrophysics professor Pawan Kumar, the Max Planck Institute for Extraterrestrial Physics in Germany will also be documenting the collision.