Two years ago, astronomers realized that a gas cloud was on a collision course with the supermassive black hole at the center of our galaxy. The encounter has since taken place — and it was all recorded in real time. Here's how it all went down — and a stunning simulation to go along with it.
The astronomers, who used the ESO’s Very Large Telescope (VLT) to chronicle the event, aren’t entirely sure where the gas cloud came from. It could have been created by stellar winds from the stars orbiting the black hole, or the result of a jet from the galactic center.
Regardless, its encounter with the Milky Way’s central supermassive black hole was a close shave indeed. The cloud’s closest approach was a distance equal to five times the distance of the planet Neptune to the Sun (about 25 billion kilometers). That’s astounding given that we’re talking about an object with a mass four million times that of the Sun; any closer and the entire thing might have fallen completely in.
As a result, the gas at the head of the cloud has been stretched to over 160 billion kilometers around the closest point of the orbit to the black hole. What used to look like a circular blob now looks like a long, thin strand of spaghetti. And in fact, the extreme elongation of the cloud means that it’s no longer a singular event, but rather a process that’ll take over a year to unfold.
Another effect of the encounter is that the head of the cloud is now coming back at us at more than 10 million km/hr along the orbit. That’s about 1% of the speed of light! It also means that the head has made its closest approach to the black hole. The tail itself is a bit slower, chugging along at about 700 km/s.
The event was recorded this past April with the VLT in Chile. The team, which was led by Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Germany, used a 20-hour exposure with a special infrared spectrometer, called SINFONI, to measure the faint light.
Image: VLT observationsf from 2006, 2010, and 2013, colored in blue, green, and red respectively. Credit: ESO/S. Gillessen.
The research was presented in a paper "Pericenter passage of the gas cloud G2 in the Galactic Center." It’s set to appear in an upcoming edition of the Astrophysical Journal.