A group of astronomers headed by Dr Andreas Eckart from the University of Cologne, Germany, has made the best observations so far of a dusty red object at the Milky Way’s galactic center, known as G2, using the SINFONI instrument on the European Southern Observatory’s Very Large Telescope (VLT) in Chile. According to the group, G2 made its closest approach to the Milky Way’s supermassive black hole, Sagittarius A*, in May 2014 and has survived the experience.
This composite image shows the motion of the dusty cloud G2 as it closes in, and then passes, Sagittarius A* – the Milky Way’s supermassive black hole. Image credit: A. Eckart / ESO.
G2 is a dusty red object located approximately 26,000 light-years away from the Solar System.
The object, which was discovered in 2002, has been observed to be disrupting since 2009, and was predicted by some scientists to be completely destroyed in 2014 by a close encounter (peribothron) with Sagittarius A* at a distance of 3,000 times the radius of the black hole’s event horizon.
The great tidal forces in this region of very strong gravity were expected to tear G2 and disperse it along its orbit. Some of this material would feed the black hole and lead to sudden flaring and other evidence of the monster enjoying a rare meal.
To study these unique events, the region has been very carefully observed over the past few years by many teams of astronomers.
Dr Eckart and her colleagues has observed the region using the VLT telescope over many years, including new observations from February to September 2014, just before and after the peribothron event in May 2014.
The images of infrared light coming from glowing hydrogen show that G2 was compact both before and after its closest approach, as it swung around the black hole.
Before closest approach, the object was found to be traveling away from us at 10 million km per hour and, after swinging around the black hole, it was measured to be approaching us at 12 million km per hour.
Although earlier observations had suggested that G2 was being stretched, the new VLT observations did not show evidence that the object had become significantly smeared out, either by becoming visibly extended, or by showing a larger spread of velocities.
In addition, the NACO instrument on the VLT revealed that the behavior of the material being accreted onto Sagittarius A* is very stable, and has not been disrupted by the arrival of material from the cloud.
The resilience of G2 to the extreme gravitational tidal effects so close to the black hole strongly suggest that it surrounds a dense object with a massive core, rather than being a free-floating cloud.
This is also supported by the lack, so far, of evidence that Sagittarius A* is being fed with material, which would lead to flaring and increased activity.
“We looked at all the recent data and in particular the period in 2014 when the closest approach to the black hole took place,” said Dr Eckart, who is the second author of the paper published in the Astrophysical Journal Letters (arXiv.org preprint).
“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.”
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M. Valencia-S et al. 2015. Monitoring the Dusty S-cluster Object (DSO/G2) on its Orbit toward the Galactic Center Black Hole. ApJ 800, 125; doi: 10.1088/0004-637X/800/2/125
