In 1915, more than one hundred years ago, Albert Einstein published a theory of space and time or "spacetime" to be exact. One of the crucial predictions of this theory was the bending of light as it approached closer to the sun, and twice as much, as that implied by the classical newtonian mechanics (the system used before general relativity).





This additional bending of light was seen to be true in an experiment led by English astronomer Arthur Eddington in 1919. After this observation, the theory of general relativity was started to be taken seriously as it resurrected the idea of a black hole which was first proposed in 1783!





Just about a year after its publishing, another German physicist by the name Karl Schwarzschild used Einstein's field equations to calculate the radius up to which any object of mass must be "cramped" so as to make it a black hole. This is called the Schwarzschild radius.





Earth reduced to the size of a pea will become black hole





But even though the theory of general relativity had suggested the existence of a powerful space object from which not even light could escape, Einstein himself wrote in a paper claiming that a star would never shrink to zero size.





Anyway, in 1930, Indian physicist Subrahmanyan Chandrasekhar calculated that stars heavier than the sun could actually collapse when they "ran out of hydrogen" or other nuclear fuels to burn. A white dwarf with mass greater than the Chandrasekhar limit is subject to further gravitational collapse evolving into a different type of stellar remnant.





Then in 1939, American physicist Robert Oppenheimer produced a paper titled, " On Continued Gravitational Attraction " and in it calculated that a star would have to be at least three times as massive as the sun to form what is today known as a black hole. T his paper was the key factor in the rejuvenation of astrophysical research in the United States in the 1950s, mainly by John Archibald Wheeler.





In fact, the term black hole was first used in 1967 by Wheeler himself during a talk he gave at the NASA Goddard Institute of Space Studies. Not even light could escape from it, hence, "black" hole. From the outside, one could not tell what was inside the black hole and Wheeler called this, "A Black Hole Has No Hair". This means that the black hole contains a lot of information which is hidden from the outside world.





But in 1971, the idea that "information" may be transferred from a rotating black hole to an outside particle was proposed and its mechanism explained by mathematical physicist Roger Penrose. Three years later, in 1974, another explanation for the same was provided by cosmologist Stephen Hawking as in Hawking radiation.





Stephen Hawking at Kennedy Space Center, NASA





Around the same time, physicist Kip Thorne, one of Wheeler's doctoral students, developed the general relativistic theory of thin accretion disks around black holes, a flattened band of spinning matter around the event horizon, which you may have seen in artist's impressions of the black hole . He compiled this and many other theoretical results about the black holes in a 1994 book for non-scientists.





More recently, Thorne was involved in the making of the hit movie "Interstellar" along with film director Christopher Nolan. He acted as the scientific consultant as well as the executive producer of the film. The science fiction project not only generated a fortune at the box office but also a "new public interest" regarding the black holes.





An artist's interpretation of a black hole





Therefore, the release of first picture of the black hole in Messier 87 is yet another beautiful step forward in the field of astrophysics. The collective effort of scientists from over 20 countries has made it possible to see the distant space object by converting the entire planet Earth into a giant virtual telescope!





It really confirms how fortunate we are as a species at this particular time, with the capacity of the human mind to comprehend the universe, to have built all the science and technology to make it happen.





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