Black Hole Image: India’s Contribution in This Feat Will Wow You!

Vishal Chauhan, 15/04/2019
Black Hole Image: India’s Contribution in This Feat Will Wow You!

Some hours ago astrophysicists brought us the real look of a far away black hole for the first time in history. Numerous science fiction writers, artists, and thinkers have dreamt and visualised the image of a black hole before. But, this is the first time we see a real image of a black hole using powerful (wo) man-made telescopes.

The target was a super massive black hole located at the centre of the Messier 87 (M87) galaxy about 500 million trillion km away from Earth. It measures 40 billion km across, roughly 3.3 million times the size of the Earth.
Let that sink in.

Black Holes & ‘Chandrasekhar Limit’

Black holes are mystery objects which have such immense gravitational fields that even light cannot escape. Existence of black holes in the universe was part of the prediction from Albert Einstein’s General Theory of Relativity.

Interestingly, it was the Nobel Prize-winning Indian American astrophysicist S Chandrasekhar, the nephew of the legendary Nobel Laureate C V Raman, who predicted at what mass a star, could or could not collapse into a black hole. This is called the ‘Chandrasekhar Limit’ in astrophysics. 

The limit explains that when a star’s mass is lighter than 1.4 times that of the sun, it eventually collapses into a denser stage called a “white dwarf.” When heavier than 1.4, a white dwarf can continue to collapse and condense, evolving into a black hole or a supernova explosion.

Google Doodle illustrates one of the most important of all of S. Chandrasekhar’s contributions to our understanding of stars and their evolution: The Chandrasekhar limit. Google Doodle illustrates one of the most important of all of S. Chandrasekhar’s contributions to our understanding of stars and their evolution: The Chandrasekhar limit. Photo Courtesy: Google Doodle)

Prof Priyamvada Natarajan, an astrophysicist at Yale University, exclaimed that Einstein must be delighted at the moment. She added “his theory has just been stress-tested under conditions of extreme gravity, and looks to have held up”.

All the matter and energy sucked into the black hole ends up at a point called singularity, where huge amounts of matter and energy are crushed into an infinitely small space. American physicist Prof Kip Thorne explains it as “a location where the laws of physics break down.” All this shows that black holes are certainly enticing to study.

Black Hole Image: What Did We Actually See?

Latest images have shown a ring-like structure with a dark central region — the shadow of the Messier 87 black hole. This is called “supermassive” because this black hole has a mass about 6.5 billion times the mass of the Sun.

What we see in the latest images are the signatures of particles outside the event horizon (like the boundary line of black holes) and not the inner core (which is invisible) of the black hole. Until now black holes have only been observed indirectly due to their gravitational influences on other stars and the motion of such celestial objects.

The whole thing can be seen as a bright disc of glowing gas in the image where the black hole is expected to create dark regions like making a shadow. The bright halo is caused by superheated gas falling into the black hole. The boundary where the shadow begins marks the “event horizon”, the region around the centre of the black hole from where matter and energy cannot escape the black hole’s gravity or fondly called as ‘point of no return’!

How Jagdish Chandra Bose Helped Getting the Black Hole Image?

“Super massive black hole residing at the centre of our own galaxy has the largest angular size in the universe found as of now, the second largest being the supermassive black hole at the centre of the active galaxy M87. For our our own galaxy, the electromagnetic radiation (the optical part) gets obscured by a dust band running through the equatorial plane of our galaxy and hence one can observe the horizon by using the radio telescopes only” comments Prof Tapas Kumar Das, a senior theoretical physicist based at Harish Chandra Research Institute, Allahabad.

“On the other hand, because of its very large wavelength, the size of a radio telescope to resolve such a tiny angular structure should be extremely large, effectively of the order of 5000 kilometer, and such a huge single telescope is impossible to construct. Scientists, however, created an effective earth sized telescope by using an array of radio telescopes located at various sites of the Earth" adds Prof Das, the only Indian physicist who works on black hole shadow imaging.

Telescope network consisting of eight radio telescopes forming the Event Horizon Telescope (EHT) helped astronomers to image the black hole at such a large distance.

Thus, it acted as an Earth-sized virtual observatory to study the external black hole. The EHT network telescopes in Hawaii, Mexico, Spain, Chile and Antarctica use the Earth’s rotation to serve as a single giant telescope. It can resolve objects into precision of 15 to 20 micro arc seconds, almost like trying to spot a typical golf ball on our far away moon.

These telescopes operated at range of frequencies first generated by Indian physicist Jagdish Chandra Bose in Bengal about 100 years ago.