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Dusty cloud G2 passes the supermassive black hole

Mysterious flare emitted by the supermassive black hole of our galaxy

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 

black hole winds

Astronomers discover a super-fast star thrown out of the Milky Way

Many stars orbit near the Sagittarius A*, which is the super-massive black hole at the centre of the Milky Way galaxy. Some stars have been ripped apart when they got too close to the super-massive black hole. Other stars have changed colour due to the extremely high gravitational effects and in a few cases, the stars just slingshot into the intergalactic space like the S5-HVS1 star.

As reported in a paper available on the pre-print server arXiv, yet to be peer-reviewed, an international group of scientists have spotted a hypervelocity star as they were studying interesting objects for the Southern Stellar Stream Spectroscopic Survey(S5). The speed of hyper-velocity refers to a staggering 1,107 kilometres per second which is equivalent to 2.275 million miles per hour and could cover the distance between New York and Sydney in just 15.7 seconds.

There must be something that has accelerated to move the star at such high speed and a team of researchers are trying to estimate from where the star could most possibly come from. The most likely explanation based on their analysis is the core of the milky way which easily refers to the Sagittarius A*.

If the super-massive black hole is the real reason, then the star was probably kicked away with a velocity of more than 1800 kilometres per second and has been slowing down on its travel for about 4.8 million years. The star is a standard hydrogen fusing star or the main sequence object and is located close to 30,000 light-years from the Earth.

It is the fastest main sequence star which was ever discovered and it is not unique as astronomers have discovered dozens of stars like these and although many of such stars appear to have accelerated out of the galaxy by events other than the interactions with Sagittarius A*. Researchers are suggesting that if one of the two stars in a binary system goes supernova, it could be enough to push its companion beyond the disk of the Milky Way.

However, the stars are not only being kicked out as scientists have detected stars entering the galaxy from the smaller companions of Milky Way. They could have been also accelerated by a supernova or a supermassive black hole yet to be observed.

Journal Reference: arXiv


S2 passing supermassive black hole

Einstein’s General Relativity has passed a huge test in the centre of our galaxy

The theory of General Relativity explained by Albert Einstein in 1915 has yet again been confirmed by another test of a star orbiting our galaxy’s supermassive black hole at insane speed. The study has been published in the Science journal. When the light of a star named S2 approached closest around the black hole, gravitational redshift was observed, stretching out the light by the strong gravitational forces involved.

Last year, a team of researchers announced a similar achievement on S2 or S0-2, one of a group of young, large S-stars orbiting the galactic centre showing clear evidence of gravitational redshift while looping around Sagittarius A*. This new result is from an independent observation set which confirms and elaborates on the first group of results with additional instruments and data for ruling out the biases which might have originated in the tools.

Astronomer Andrea Ghez of the University of California, Los Angeles said that their observations are consistent with Einstein’s theory of general relativity and can definitely rule out Newton’s law of gravity. After 24 years of observation with the sensitive instruments enough to observe the phenomenon in exceptional resolution, it was last year when the star S2 which takes 16 years to orbit Sgr A* was at the closest approach within 17 light-hours of the galactic centre around Sgr A*.

The gravity produced by Sgr A* having a mass equivalent to about 4 million suns is enormous and creates the most extreme condition in the Milky Way. The elliptical path of S2 gets accelerated to stunning speed by this gravity and slingshots around at 25 million kilometres per hour (15.5 million miles per hour) – almost 3 percent of the speed of light. According to relativity, the light of stars should expand into longer wavelengths, towards the red end of the electromagnetic spectrum by the gravitational effect when it comes close to the black hole.

Researchers made spectral observations of the incidents of last year when it reached its maximum velocity in March, followed by closest approach in May, and minimum velocity in September by studying the variations in star’s light as it hurtled around the black hole and finally merging all the spectral observations from 1995 to 2017 to remodel the complete orbit of the star in three dimensions.

Ghez said that study of the motion of stars going through their complete orbit will enable the possibility for the study of General Relativity, fundamental physics and the accurate explanation of the behaviour of a star near a supermassive black hole. These results boost up the outcomes of last year, approving general relativity as strong aspect in understanding the dynamics of gravity.

The test, General relativity has passed in recent times like seeing a three-body star system, an entire galaxy bending space, and the discovery of gravitational waves shows that Einstein’s 100-year-old theory still holds true. Ghez said that at some point we need to shift away from Einstein’s theory because of its vulnerability and develop a universal theory of gravity that completely explains the phenomenon of gravity inside a black hole.

Journal Reference: Science journal