In 2011, astronomers were getting excited for what promised to be a spectacular cosmic event.
Rapidly approaching our galaxy’s central supermassive black hole was a stream of gas, likely stripped from a doomed star, that seemed destined to be swallowed in the black hole’s gravitational well. But what was going to happen when the gas made contact with the black hole’s accretion disk?
It was hoped that a violent interaction would take place and observatories would see some powerful flaring events at the center of the Milky Way, providing a valuable insight to the eating habits of supermassive black holes that are thought to reside in the centers of most galaxies.
Now the time has come — what are astronomers seeing? Well… not a lot. It seems that the cloud of gas, known simply as “G2,” isn’t generating the fireworks it seemed destined to.
Flaring supermassive black holes have been observed before in other galaxies. By looking at the energetic radiation generated by these events, astronomers can surmise what the black hole has “eaten.” Stars, planets, gas clouds, even asteroids have been seen being blended by the gravitational behemoths. So to have the possibility of seeing our very own supermassive black hole — known as Sagittarius A*, or simply Sgr. A* — light up while munching on G2, astronomers were very excited for the scientific opportunity.
Sadly, just as the streamer was predicted to be interacting with Sgr. A* during an observing campaign this spring, they saw nothing.
In a new paper published to the arXiv preprint service this month, Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and his colleagues gave an explanation as to why the stream of gas may not be kicking off the display astronomers hoped.
Gillessen, who used the European Southern Observatory’s Very Large Telescope in Chile to discover that G2 was approaching Sgr. A*, suggests that the streamer’s interaction with the black hole’s accretion disk is a lot more subtle than they were expecting.
It appears that G2 is composed of one gravitationally-bound clump and a less dense stream of gas that is steadily rushing into the accretion disk like a breeze and not in a clumpy, energetic manner as predicted.
The researchers have also worked out that another clump of gas that interacted with the black hole over a decade ago, known as “G1″, is related to G2 as both are following the same orbital path. It is thought that both clumps were stripped from the same star 100 to 200 years ago.
This theory was also examined by another research group headed by James Guillochon and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
But, as discussed by today’s Nature News article, it’s possible that the G2 clump is hiding a star that is gravitationally binding the majority of the material, preventing it from being pulled into the black hole’s accretion disk.
Whatever the mechanisms behind the drama unfolding in the center of our galaxy, one thing is clear: our supermassive black hole does not have the munchies (yet).