Subramanyan Chandrasekhar - an Astrophysicist Par Excellence

Chandrasekhar was one of the great astrophysicist of our time. He was also the greatest master of the English language. (Hans Bethe)

I don’t remember in any precise detail as to how, or even exactly when, I came to know about Subramanyan Chandrasekhar, who preferred to be called Chandra. Although I remember reading about him in “A Brief History of Time” by Stephen Hawking (the book was published in 1990), I have a feeling that I knew of him long before. Early in 1969 when I was at Imperial College, London, one day I was browsing books in one of the local area book shops around lunch time. Suddenly the title of a book, Hydrodynamic and Hydromagnetic Stability, caught my eye. Although I knew it wouldn’t be of much use to me in my work, I picked up the book out of curiosity and read the name of the author; it was Subramanyan Chandrasekhar. Later on, I tried to find more information about him and believe I did find some bits and pieces. I had run into Ramanujan’s name also about that time in a library.

Ever since, I learnt about Chandra, I was completely impressed (obsessed!) by him. And now here I am paying homage to the great scientist that Chandra had been.

Chandra was a south-Indian (Tamil) although he was born in Lahore (October 19, 1910). His father was a civil servant in Indian Railways and it was during his tenure of service in Lahore that Chandra was born. His father’s name was C.S. Ayyar. Chandra was the oldest of the ten children of his parents (According to Hans Bethe, The Ayyars had three sons and five daughters of whom Chandra was the oldest son….). The Nobel laureate C.V. Raman was his maternal uncle.

At the age of 15, he entered Presidency College in Madras, which was one of the most prestigious institutes in India at that time. He read the physics honors course in 1927 and finished it in 1930 at the head of his class. He won a government scholarship for higher education at Trinity College, Cambridge, England. While still an undergraduate at Presidency College, he read Ralph Fowler’s work on the constitution of the white dwarfs. This inspired him to write his first research paper, “Compton Scattering and the New Statistics,” which he sent to Fowler at Cambridge. Fowler was so impressed by his paper that he sent it for publication in the “Proceedings of the Royal Society.” It was published in 1928 when Chandra was only 18. By virtue of this paper, Fowler accepted him as a research student at Cambridge. His second paper was published in Philosophical Magazine.

At a young age, he was inspired by Ramanujan. According to Nitin Ingle (Ramanujan’s Influence on S.C. Chandrasekhar, a talk given at the SPIC-MACAY meeting, Buffalo, New York), “Ramanujan greatly influenced S.C; he was his role model for a life dedicated to the pursuit of science. S.C. was not quite ten years old when his mother told him about a famous Indian mathematician, Ramanujan by name. At that time, neither Chandra nor his mother had any idea what kind of mathematician Ramanujan was.”

Abdus Salam, when he was an undergraduate at Government College, Lahore, was also influenced by Ramanujan. Salam’s first paper was on an improvement of Ramanujan’s work. According to Tom Kibble (Emeritus Professor Abdus Salam, Nobel Laureate, staff newspaper of Imperial College), “It was an ingenious improvement on the solution of an algebraic problem discussed earlier by the Indian mathematical genius Srinivasa Ramanujan.”

It is reported that initially Chandra’s mother didn’t want him to go to England but the desire for her son to excel like Ramanujan and surpass his uncle Raman settled the issue. She was not feeling well at the time Chandra was to embark upon his journey but she saw him off with a happy heart. He left Bombay on July 31, 1930 by ship. After overcoming his seasickness during his two and a half week voyage, he fished out Fowler’s paper and started working to combine it with the theory of special relativity. The result was both surprising and novel. He found that his result “predicted that white dwarfs could only exist up to a certain limiting mass which depended chiefly on fundamental constants such as h (Planck’s constant), G and the mass of the hydrogen atom; the limiting mass was about 1.45 times the mass of the Sun.” This limit is now called Chandrasekhar’s mass limit.

In 1930, he made another important discovery which was destined to make him a leading astrophysicist in the world. The implications of this result were not immediately clear to many at Cambridge. According to Bethe (A Tribute to Subrahmanyan Chandrasekhar – 1983 Physics Nobelist, http://www.tamil.net/people/andrew/subra.htm), “England’s two leading astrophysicists, Eddington and Milne, could not believe this result, and neither of them would recommend Chandra’s paper for publication by the Royal Society. So Chandra sent it to the Astrophysical Journal in America, which published it in March 1931.”

One of the objections was that the Pauli exclusion principle could not be applied to a relativistic system. Several top physicists including Leon Rosenfeld, Niels Bohr, Wolfgang Pauli, and Paul Dirac privately supported his result but abstained to do so publicly. Chandra received his Ph.D in 1933 for a thesis on rotating self-gravitating polytropes. He was elected a fellow of Trinity College.

After finishing his Ph.D, he returned to the problem of the white dwarfs. He decided to present his work in a paper at the meeting of the Royal Society on January 11, 1935 where Eddington also presented his work. This story has been told and retold by many but the best account that I know of is given by John Tierney (Quest for Order, in “The World Treasury of Physics, Astronomy, and Mathematics,” ed. Timothy Ferris, pp.606-607). It is worthwhile to reproduce the following rather large narrative from him:

He (Chandra) arrived in London that Friday with great expectations for himself and mild suspicions concerning Sir Arthur Eddington. For months he and Eddington had been getting together, about twice a week after dinner, to discuss Chandrasekhar’s latest calculations about the behavior of dying stars. They made an odd couple: the famed Eddington, eloquent, prepossessing, at fifty-two generally acknowledged as the world’s finest astronomer, listening eagerly to a shy twenty-four-year-old from India who felt himself something of an outcast at Cambridge University………

But the day before, when a copy of the program for the meeting had arrived in Cambridge, Chandrasekhar had been amazed to discover that Eddington would also be speaking at the meeting. On the same subject. During all their discussions, while Chandrasekhar had been spewing out his figures, Eddington had never mentioned any work of his own in this area. It seemed an incredible breach of faith, yet Eddington offered no apology or explanation when the two men saw each other in the dining hall Thursday evening…….

Chandrasekhar’s paper dealt with a fundamental question: what happens after a star has burned up all its fuel? According to the prevailing theory of the day, the cooling star would collapse under the force of its own gravity into a dense ball called a white dwarf. A star with the mass of the Sun, for instance, would shrink to the size of the earth, at which point it would reach equilibrium. Chandrasekhar studied this collapse by considering what happens when a star’s gas becomes so compressed that electrons move at nearly the speed of light – a state called relativistic degeneracy. He concluded that the enormous gravitational forces at work in a large star – any star more than 1.4 times as much massive as the sun – would cause the star to go on collapsing beyond the white dwarf stage. The star would simply keep getting smaller and smaller and denser and denser until….well, that was an interesting question. Chandrasekhar delicately avoided it. “A star of large mass cannot pass into the white dwarf stage,” he concluded, “and one is left speculating on other possibilities.”

Then it was Eddington’s turn.

“I do not know whether I shall escape from this meeting alive, but the point of my paper is that there is no such thing as relativistic degeneracy,” said Eddington, and proceeded to tear apart Chandrasekhar’s paper. The speech was frequently interrupted by laughter. Eddington couldn’t quarrel with Chandrasekhar’s logic or calculations. But he claimed that the whole theory had to be wrong simply because it led to an inevitable and outlandish conclusion.” “The star has to go on radiating and radiating and contracting and contracting until, I suppose, it gets down to a few kilometers radius, when gravity becomes strong enough to hold in the radiation, and the star can at least find peace.”

Today, of course, such an object is called a black hole. That afternoon, Eddington said it couldn’t possibly exist.

“A reductio ad absurdum,” he called it.” “I think there should be a law of nature to prevent a star from behaving in this absurd way.”

Eddington’s supposition was wholly correct but he was caught in the web of his predetermination and eloquence. That was a fateful speech which held back Chandra’s soaring to deservingly new heights, for several decades, and earned Eddington a permanent historic black spot which is hard to erase and forget.

Although Chandra had a paid position at Cambridge, his chances of further improvement were blocked by Eddington. Under these circumstances, he applied for a suitable position at the University of Chicago where he was offered employment at Yerkes observatory. The employment at Chicago University was a lifelong engagement; he was at Yerkes for 27 years and at Fermi’s Research Institute for 31 years.

He started work at Yerkes in 1937 but before going there directly, he went to India first to marry his old friend Lalitha Doraiswamy in 1936 who was working at that time “in the Bangalore laboratory of his uncle Nobel laureate Chandrasekhra Venkata Raman.” He became a U.S. citizen in 1953. He was Morton D. Hall Distinguished Professor in Astronomy and Astrophysics when he died in 1995 after a service of 58 years with University of Chicago.

His career was crowned with the award of Nobel Prize in physics which he shared with William A. Fowler (not related to Ralph Fowler at Cambridge) in 1983, “for his studies on the physical processes important to the structure and evolution of stars.” He was somewhat fazed because “the citation mentioned only his earlier work, seeing this as a denigration of a lifetime’s achievement,” (wikipedia). NASA named the third of its four “great Observatories” after him, The Chandra X-ray observatory. The asteroid 1958 Chandra is also named after him. In addition to his Nobel Prize, he was also honored with the following awards:

• Henry Norris Lectureship (1949)
• Bruce Medal (1952)
• Gold Medal of the Royal astronomical Society (1953)
• Royal Medal of the Royal society (1962)
• Henry Draper Medal (1971)
• Copley Medal of the Royal society (1984)

Although Chandra was bitter about Eddington’s treatment, they let “bygones be bygones” eventually. Eddington promoted Chandra’s election to the Royal Society in 1944. According to Eugene Parker, a colleague at University of Chicago, “In spite of the difficulties that Eddington’s mulish attacks had created for him, Chandra ranked Eddington next to Karl Scharwzschild as the greatest astronomer of his time when he presented an obituary address for Eddington in 1944, “ (Physics Today, November 1995, pp. 107-108).

According to Martin Schwarzschild, “There is total unanimity among astronomers that Chandrasekhar, as a mathematical astrophysicist, was the greatest of our generation;” and according to Norman Lebovitz, “He was the most intellectual of intellectuals, and the most tireless worker in science.”