Black holes are a consequence of Einstein's field equations. His magnum opus, the Theory of General Relativity radicalized our understanding of gravity and offered a very different explanation from the Newtonian idea of how gravity worked.
Gravity, said Einstein, is not a force as Newton wanted us to believe, rather, it is a result of the warping, or curving, of space and time. At the heart of this radical upheaval was the idea of how mass distorts the space-time.
The first-ever image of a black hole, from the M87 galaxy located in the Virgo constellation in the Milky Way. Image: EHT/NSF
General Relativity made some radical predictions about how this curving of space-time works. It predicted that a massive, accelerating objects like two neutron stars or black holes can generate ripples in space-time, called gravitational waves. In a groundbreaking experiment by >Laser Interferometer Gravitational Wave Observatory (LIGO) confirmed the existence of gravitational waves in 2015 when it captured a wave created by two colliding black holes nearly 1.3 billion light-years away.
It also predicted the existence of bodies with a sufficiently large mass that would have an escape velocity exceeding the speed of light, making it a bottomless pit of cosmos. These heavily dense objects(that would eventually be called black holes) would distort the fabric of space-time that nothing, not even light can escape its gravitational field. In 1916, a year after Einstein published his Theory, Karl Schwarzschild discovered a solution to Einstein's equations of general relativity and mathematically proved the existence of black holes. In 1935, Indian astrophysicist Subrahmanyan Chandrasekhar >scientifically proved that a massive star when runs out of nuclear fuel, its pressure is insufficient to counter the gravitational pull and nothing can pass through it, not even light.
But, the idea was so radical, that Einstein himself was not convinced with such a reality. In a 1939 paper, >he concluded that the idea was "not convincing" and the phenomena did not exist "in the real world."
Massive jets propelling away from the black hole at the center of Centaurus A galaxy 13 million light-years away. The jets alone stretch further in space than the galaxy itself. Image: ESO/WFI/MPIfR/APEX/NASA/CXC
It took us more than a century, but we are finally beginning to map his math with reality. A black hole located 55 million light-years from Earth was recently captured by Event Horizon Telescope (EHT), a network of eight linked telescopes, making it one of the first black holes to be captured in a close-up image.
The newly pictured M87 *, the black hole you've seen everywhere has a name too. Astronomers have> decided to call it "PÅwehi," which means "embellished dark source of unending creation" in the indigenous Hawaiian language. Astronomical naming conventions are complex and sometimes, weird. Like the craters on the Mars, less than 60 km in diameter >should be named after "villages of the world with a population of less than 100,000", which is why a multi-layered volcanic crater on Mars is called "Tooting", named after a London suburb.
But, the term, "Black Hole" has an interesting, deep and dark tale of its own.
The Melancholy of Dying Stars
Towards the end of the 1960s, the astrophysics world was beaming with groundbreaking discoveries. Cosmos was beginning to suggest that space is peppered with the melancholy of heavy densely packed dying stars, black holes. The traditional version of the story traces the origins of the term to December 1967, when an American theoretical physicist, John Archibald Wheeler used it during a lecture in New York City. However, in his autobiography, titled "Geons, Black Holes and Quantum Foam", he recalls that the term was in fact suggested to him during another lecture when someone from the audience got really tired of hearing Wheeler repeatedly saying "gravitationally completely collapsed object."
The fictional Miller's planet orbiting the black hole 'Gargantua' in the movie Interstellar. Image: Interstellarfilm.wikia.com/Paramount Pictures
But, that was not the first instance when the term "Black Hole" appeared in the scientific literature. In the January 24, 1964 issue of Life Magazine, long before Wheeler's lecture, Life's editor AI Rosenfeld >used the term in a report titled 'Heavens' New Enigma' discussing Einstein's theory of relativity and the newly discovered "Quasi-stellar" objects, covering a meeting that took place in Dallas, in July 1963, at the Texas Symposium on Relativistic Astrophysics.
This, however, was not the first time when the term black hole was used in print. Turns out, around the same time in January 1964, at a meeting of the American Association for the Advancement of Science (AAAS) in Cleveland, USA, the term was used to define what then known as 'degenerate stars'. Science News magazine carried >a report by Ann Ewing on this meeting, describing how intense gravitational field could cause a star to form a 'black hole' in the space, in its January 18,194 issue. And this is when the term 'black hole' made its first print appearance.
MIT Professor and science writer, Marcia Bartusiak traces the origins of the term 'black hole' in her book >Black Holes. Bartusiak writes that it was Hong-Yee Chiu, an American Astrophysicists of Chinese origins, who also coined the term "quasars", organized the January 1964 AAAS talk at Cleveland. Chiu first stumbled upon the term in a seminar at Princeton, in the early 1960s, where physicist Robert Dicke was explaining the dense stars collapsing in their own gravitational field. Dicke described these objects as "like the Black Hole Of Calcutta"- a prison so bad that people went in but did not come out. In fact, it appears that Dicke used the phrase quite liberally, Bartusiak notes that Robert Dicke's children >remember their father saying "Ah, it must have been sucked into the black hole of Calcutta" whenever something got lost at their house.
So, what is that black hole of Calcutta, Dicke referring to?
The Siege Of Calcutta
In April 1756 CE, Mirza Muhammad Siraj Ud-Daulah ascended the throne of Bengal. By then, East India Company had already established itself in Calcutta " on an expansion spree. After a war with the Mughals, the Company's main Bengal trading station was moved from Hooghly (now Hugli) to Calcutta and operated from Fort Williams, named after King William III of England. The fort doubled as a symbol of security and a trading center.
The fortification and the gradual expansion by British occupation didn't go well with newly ascended Nawab of Bengal. Fort William, which was then headed by Governor Roger Drake, simply ignored Nawab's repeated warnings against the expansion and fortification. Sensing the British indifference to Siraj's authority, he organized his army of 50,000 troops and marched towards Calcutta to siege the Fort. At this point, East India Company was still a trading body with at most 250-odd Europeans to defend itself and lacked any organized war defense mechanism.
Guarding the fort against an army of 50,000 troops was a no contest. Governor Drake quickly realized this and after two days of fighting, he escaped to Phalta, leaving behind some Anglo Indian soldiers and civilians, under the command of a senior bureaucrat, John Holwell.
Inscription on Black Hole of Calcutta memorial St John's Church Calcutta. Image: Wikimedia Commons
On the night of 20th June 1756, Holwell surrendered and Siraj's army entered the Fort Williams from the Northern River gate. The captives were then confined for a night in a small room measuring 14 feet by 8 feet leading to the infamous "Black Hole Of Calcutta" tragedy. Holwell, who survived the night, alleged that more than 145 Europeans were confined in a "Black hole" and out of 146 prisoners, only 23 survived. The remaining 123 died of suffocation and died. Historians and researchers have contested Holwell's account, claiming it is simply not possible to confine nearly 150 persons in a room of that size. The numbers might have been exaggerated,but it has not stopped the idiom from being used and the term ended up being the most talked about term in the scientific literature.
Siraj later demolished the fort and a new fort Williams was constructed further south, now known as Maidan. The original William Fort stood in present-day Dalhousie Square in Kolkata's central business district, between Fairlie Place and Koila Ghat street. Today, it houses GPO, RBI and Eastern Railway Headquarters. The original location of the black hole can be accessed through a narrow passageway by the northern side of the present Post Office building, which now serves as a dump of garbage.
In the memory of those who died on that fateful night, Holwell erected an obelisk at present-day BBD Bagh North and NS Road crossing. But the inscription had only a few names and it fell into despair after the fort was demolished. In 1902, Lord Curzon >re-erected the monument with names of 123 people who perished in the tragedy. Today, the monument stands in the compound of St John's Church. A closer look of the monument reveals that one of the people who died in the Black Hole tragedy was a gentleman named >Stair Dalrymple, ancestor of the author and Mughal historian William Dalrymple. The same compound houses the memorial of his another forebear and the protagonist of "White Mughals", James Achilles Kirkpatrick, the Majnu-esque lover of Khair un-Nissa.
On your next trip to Kolkata, if you find yourself around Dalhousie Square, then you are at the heart of a historic battleground. It's here that a battle was fought, which changed the history of British occupation in Bengal and led to another war- the battle of Plassey. It's here that the idea of "matter tells Space-time how to curve, and Space-time tells matter how to move." was first put to test, which changed the literature of astrophysics forever- and for good.
After all, "gravitationally completely collapsed object", is indeed, too much of a mouthful, something which Einstein would have never approved of.