The center of our galaxy is home to a supermassive black hole named Sagittarius A* and we’ve been watching for more than a year to see if the monster was about to gobble up a gas cloud. Anticipating the event wasn’t entirely voyeuristic—astronomers were eager to see a black hole in action. But the gas cloud has escaped from the gravitational clutches and its fate.
The object’s ability to elude the Milky Way’s black hole has to do with some unexpected qualities: The cloud, called G2, isn’t a cloud at all. The sheer fact of its escape means that it must contain a star. Jenny Winder for SEN.com writes:
The object, known as G2, was discovered in 2011 by a team of astronomers at the Max Planck Institute for Extraterrestrial Physics in Germany, led by Stefan Gillessen. They used the European Southern Observatory’s Very Large Telescope (VLT) in Chile to observe in the infrared, and so view through intervening dust. Gillessen believes it to be a dense stream of hydrogen gas. But now, a new study of G2, led by Andreas Eckart of the University of Cologne in Germany, has come to a different conclusion—that it is a single object with a dense core.
Eckart’s team peered at the galactic center and the nearby G2 for years, including the time before and after what they think was the object’s closest approach—or peribothron—to the black hole in May 2014. "The images of infrared light coming from glowing hydrogen show that the cloud was compact both before and after its closest approach, as it swung around the black hole," reports a press release from the European Southern Observatory.
The astronomers published their findings in Astrophysical Journal Letters and also released images of the close encounter. The image above is a composite image of G2 starting in 2006 (in yellow) and most recently in September 2014 (in blue). The red cross indicates the location of the black hole. For Slate’s Bad Astronomy blog, Phil Plait explains that the coloring is important:
It represents how fast G2 was moving away from Earth as it rounded the black hole (the colors were added later to represent red and blue shift). The velocity in February 2014 was away from us at about 2700 km/sec, just under 1 percent the speed of light! In September it had rounded the black hole and was headed toward us at over 3300 km/sec, an incredible speed. I’ll note it’s so far away that even at that speed it would take millennia to reach Earth, and in fact it’s in a closed orbit around the black hole, so it’s not going anywhere anyway.
In addition to the colored images, the team also released a video. “We looked at all the recent data and in particular the period in 2014 when the closest approach to the black hole took place," writes Eckart in the release. "We cannot confirm any significant stretching of the source. It certainly does not behave like a coreless dust cloud. We think it must be a dust-shrouded young star.”