Mysterious flare emitted by the supermassive black hole of our galaxy

Dusty cloud G2 passes the supermassive black hole
This composite image shows the motion of the dusty cloud G2 as it closes in on, and then passes, the supermassive black hole at the centre of the Milky Way. (Credits - Wikimedia Commons)

The supermassive black hole present at the centre of the Milky Way, Sagittarius A* has a low activity level most of the time as it is quiet, does not possess an active nucleus and has minimum brightness fluctuations. However recently, astronomers observed that its brightness increased 75 times before it went back to normal levels. 

Tuan Do, an astronomer at University of California Los Angeles said he was both surprised and excited to observe this. He even mistook it to be the star S0-2 for its brightness. Scientists have been trying to find out what is the reason behind this event. Their observations are accepted in The Astrophysical Journal Letters and can be found here


The galactic centre was observed by Do and his team with the help of WM Keck Observatory located in Hawaii. This unusual brightening was observed on May 13 for a period of two hours that was converted into a time-lapse of a few seconds. Although black holes themselves do not emit any radiation which can be detected by the instruments, the surrounding gases emit radiation due to the friction generated by the gravitational forces of the black hole. The radiation is observed as brightness when viewed in the infrared range of the telescope. When the surroundings of the black hole glow brightly it indicates that the black hole’s gravity has captured something.

The first frame of the observation is brightest indicating that the black hole might have been brighter however it was not known that any object was approaching closer to be swallowed. There are two possible situations. An object initially considered as a gas cloud, G2 was within 36 light hours of Sagittarius A* in 2014. Being a gas cloud, it would have been shredded by the black hole however this did not occur. It was later classified as a “cosmic fizzle”. 

Another possibility is that when the star S0-2 passed close to the black hole, it might have changed the pattern of gas flow into the black hole generating more variations. Having more data is the only way of confirmation, more observations are being made by the Keck Observatory as long as the centre of the galaxy is visible from Earth. Several other telescopes have also been observing the galactic centre which includes Chandra and Spitzer space telescopes. The data could help in understanding more aspects behind the change of brightness. Scientists are eagerly awaiting the results to have a better understanding.

Journal Reference: arxiv 


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