Subrahmanyan Chandrasekhar

• 1. A Ceiling for Stars

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  Subrahmanyan Chandrasekhar sailed from India to England in 1930, and on that first sea voyage he worked out a number that would outlive him. The number was 1.44. It is the greatest mass, counted in suns, that a white dwarf star can have. A white dwarf is the faded remains of a star. Add weight beyond that ceiling and the remains can no longer hold themselves up. They collapse into a neutron star or a black hole.

  The ceiling still carries its discoverer's name, the Chandrasekhar limit. Yet the limit was only the start of a working life that reached from stars to shock waves, turbulence, black holes and colliding gravitational waves. Three questions run through his story. How did a student from Madras carry such an idea into the great universities of Britain and America? What happened when a famous British physicist stood up in public and said the idea was wrong? And what sort of mind moves from one branch of physics to another every few years, leaving a book behind each time?

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• 2. Madras Beginnings

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  Lahore, then part of the British Raj and now in Pakistan, is where Chandrasekhar was born on the 19th of October 1910. His family was Tamil. His mother was Sita Balakrishnan, and his father, Chandrasekhara Subrahmanya Ayyar, was posted there as Deputy Auditor General of the Northwestern Railways. Known to everyone as Chandra, he grew up among nine siblings. His elder sisters were Rajalakshmi and Balaparvathi. His younger brothers were Vishwanathan, Balakrishnan and Ramanathan, and his younger sisters were Sarada, Vidya, Savitri and Sundari.

  Chandrasekhara Venkata Raman, his paternal uncle, was an Indian physicist and a Nobel laureate. His mother was devoted to intellectual pursuits and had translated Henrik Ibsen's A Doll's House into Tamil. She is credited with awakening Chandra's curiosity when he was very young. The family moved from Lahore to Allahabad in 1916, and in 1918 it settled for good in Madras.

  Tutors taught Chandrasekhar at home until he was 12. In middle school his father taught him mathematics and physics, while his mother taught him Tamil. He then attended the Hindu High School in Triplicane, Madras, from 1922 to 1925, and went on to Presidency College from 1925 to 1930. A lecture by Arnold Sommerfeld inspired his first paper, "The Compton Scattering and the New Statistics", written in 1929. In June 1930 he took his bachelor's degree with honours in physics.

  In July 1930 the Government of India granted him a scholarship for graduate study at the University of Cambridge. Ralph H. Fowler, to whom Chandrasekhar had mailed his first paper, was the man who secured it. The place awaiting him was Trinity College.

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• 3. Cambridge and Europe

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  Fowler became his supervisor, and the first Cambridge year went into calculating mean opacities. Chandrasekhar used the results to build an improved model for the limiting mass of a degenerate star. At meetings of the Royal Astronomical Society he met E. A. Milne.

  Max Born invited him to Göttingen for the summer of 1931, his second year of postgraduate work. There he studied opacities, atomic absorption coefficients and model stellar photospheres. On the advice of Paul Dirac, he spent his last year of graduate study, from September 1932 to May 1933, at the Institute for Theoretical Physics in Copenhagen. He met Niels Bohr there. He also lived in the same pension as Victor Weisskopf, Léon Rosenfeld, George Placzek and Max Delbrück, and the five became friends.

  His PhD came in the summer of 1933, for a thesis on rotating self-gravitating polytropes. A bronze medal for his work on degenerate stars had come first. On the 9th of October he was elected to a Prize Fellowship at Trinity College for 1933-1937. Only one Indian had won a Trinity Fellowship before him, Srinivasan Ramanujan, 16 years earlier. Chandrasekhar had been so sure he would fail that he had arranged to study under Milne at Oxford that autumn, and had even rented a flat there.

  In 1934 he travelled to Leningrad and met the astrophysicists Viktor Ambartsumian and Nikolai Aleksandrovich Kozyrev. He also met Lev Landau. Back in Britain, he grew acquainted with Sir Arthur Eddington, who took an interest in his work.

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• 4. The Eddington Quarrel

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  In January 1935 Eddington gave a talk that severely criticized Chandrasekhar's work. The occasion was a meeting of the Royal Astronomical Society, where Chandrasekhar had just presented a full solution to his stellar equation. Eddington had booked the slot right after him. He used it to attack the theory openly, in front of the whole room.

  The blow left Chandrasekhar depressed, and it began a scientific dispute. Eddington refused to accept that a star's mass could be capped at all, and he proposed an alternative model. Chandrasekhar looked for allies among prominent physicists. Léon Rosenfeld, Niels Bohr and Christian Møller each studied the matter and found Eddington's arguments lacking.

  The friction lasted through the rest of the 1930s. Eddington kept criticizing Chandrasekhar at meetings, and the two men weighed each other's theories in print. In 1939 Chandrasekhar finished his theory of white dwarfs, and others in the field praised it. Eddington died in 1944. Even after all that, Chandrasekhar went on saying he admired Eddington and counted him a friend.

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• 5. Chicago Calls

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  Harlow Shapley, director of the Harvard Observatory, invited Chandrasekhar in 1935 to serve as a visiting lecturer in theoretical astrophysics for three months. Chandrasekhar travelled to the United States in December. He impressed Shapley greatly, yet he turned down the offer of a Harvard research fellowship. During the visit he met Gerard Kuiper, a Dutch observational astrophysicist who was then a leading authority on white dwarfs.

  Otto Struve ran the Yerkes Observatory in Williams Bay, Wisconsin, which belonged to the University of Chicago. He had recently recruited Kuiper, with the support of the university's president, Robert Maynard Hutchins. Struve now had three astrophysics posts to fill, and Kuiper was one of the hires. Bengt Stromgren, a Danish theorist, took another. On Kuiper's recommendation, Struve invited Chandrasekhar to Yerkes in March 1936 and offered him the third.

  Chandrasekhar was keenly interested but refused at first and left for England. During the voyage a radiogram from Hutchins reached him, and he changed his mind. He came back to Yerkes in December 1936 as an assistant professor of Theoretical Astrophysics. Hutchins stepped in again when the dean, Henry Gale, vetoed Chandrasekhar's part in teaching a course Struve had organised, on grounds of racial prejudice. Hutchins answered, "By all means have Mr. Chandrasekhar teach".

  Chicago kept him from 1937 to 1995. He was promoted to associate professor in 1941 and to full professor two years later, at the age of 33. In 1946 Princeton offered him a position left empty by Henry Norris Russell, at double the Chicago salary. Hutchins matched the figure and persuaded him to stay. In 1952, at Enrico Fermi's invitation, he became the Morton D. Hull Distinguished Service Professor of Theoretical Astrophysics. In 1953 he and his wife, Lalitha, took American citizenship.

  NASA built the Laboratory for Astrophysics and Space Research at the university in 1966, and Chandrasekhar took one of its four corner offices on the second floor. The other corners went to John A. Simpson, Peter Meyer and Eugene N. Parker.

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• 6. A Decade at a Time

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  "What a scientist tries to do essentially is to select a certain domain, a certain aspect, or a certain detail, and see if that takes its appropriate place in a general scheme which has form and coherence; and, if not, to seek further information which would help him to do that." Chandrasekhar wrote this to explain his work. He named the prime motive behind it as systematization.

  His method followed a pattern. He would study one area exhaustively, publish several papers on it, and then write a book gathering its major ideas. Then he moved on, and the next decade belonged to a new field. From 1929 to 1939 he studied stellar structure, including white dwarfs. Stellar dynamics and the theory of Brownian motion took the years 1939 to 1943. Radiative transfer and the quantum theory of the negative hydrogen ion filled 1943 to 1950. Turbulence and hydrodynamic and hydromagnetic stability occupied 1950 to 1961. The 1960s went to ellipsoidal figures of equilibrium and general relativity. From 1971 to 1983 he studied the mathematical theory of black holes, and in the late 1980s he turned to colliding gravitational waves.

  The stellar dynamics years show the method at work. Jan Oort and others had outlined earlier models of how stars move in the Milky Way. Chandrasekhar revised them by weighing the effect of fluctuating gravitational fields on stars circling the galactic center. His answer needed a set of twenty partial differential equations. They described a new quantity that he named dynamical friction, which slows a star down and helps keep clusters of stars stable. He then carried the analysis into the interstellar medium and showed that clouds of gas and dust are spread very unevenly.

  World War II interrupted the pattern. At the Ballistic Research Laboratory at the Aberdeen Proving Ground in Maryland, he worked on ballistics. His reports included 1943's On the decay of plane shock waves, Optimum height for the bursting of a 105mm shell, and The normal reflection of a blast wave. His skill in hydrodynamics led Robert Oppenheimer to invite him to join the Manhattan Project at Los Alamos. Delays in processing his security clearance kept him from contributing. It has been rumoured that he visited the Calutron project.

  In 1975 he lectured on patterns of creativity in Shakespeare, Beethoven and Newton, for he had a strong interest in literature and the arts. From 1990 to 1995 he gave himself a last project. He set out to explain the geometric arguments in Isaac Newton's Philosophiae Naturalis Principia Mathematica using the methods of ordinary calculus. The result, Newton's Principia for the Common Reader, appeared in 1995.

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• 7. Teacher and Editor

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  Over the 50 years from roughly 1930 to 1980, the average age of Chandrasekhar's co-authors stayed around 30, and he took pride in that. He worked closely with his students. They had to call him "Professor Chandrasekhar" until they earned their PhD. After that, he and his other colleagues encouraged them to say "Chandra".

  During the 1940s he worked at the Yerkes Observatory, and every weekend he drove 150 miles each way to teach a course at the University of Chicago. Two students in that class, Tsung-Dao Lee and Chen-Ning Yang, won the Nobel Prize before he did.

  Carl Sagan remembered the lectures with some awe. Sagan said that "frivolous questions" from unprepared students were "dealt with in the manner of a summary execution", while questions of merit "were given serious attention and response". Sagan also recalled, "I discovered what true mathematical elegance is from Subrahmanyan Chandrasekhar." Over his career Chandrasekhar supervised 45 PhD students.

  From 1952 to 1971 he edited The Astrophysical Journal. In 1957 Eugene Parker submitted a paper on his discovery of the solar wind, and two eminent reviewers rejected it. Chandrasekhar, as editor, searched the paper for mathematical flaws and found none. He published it in 1958.

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• 8. The Man and His Name

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  In September 1936 Chandrasekhar married Lalitha Doraiswamy, a fellow physics student he had met at Presidency College. Her enthusiasm for physics grew from her interest in Marie Curie and from India's award of the Nobel Prize in Physics to C. V. Raman. She wanted to continue her studies in England, but her mother disagreed. She earned a teaching degree instead, in 1932, and taught physics, chemistry, math and physical education at various institutions. In 1934 she earned a master's degree in physics from Presidency College. She eventually gave up her studies and ran their household so that her husband could focus on his work. She was also a serious student of literature and western classical music.

  Opinions of Chandrasekhar differed. Many people found him warm, positive, generous, unassuming, meticulous and open to debate. Others found him private, intimidating and impatient, stubborn about non-scientific matters, and unforgiving toward anyone who ridiculed his work. He was a vegetarian. He was also an atheist, and said so plainly: "I am not religious in any sense; in fact, I consider myself an atheist." In deference to his views, Lalitha did not put out the small religious icons of deities that she had brought with her.

  In 1983 he received half of the Nobel Prize in Physics, shared with William A. Fowler, for his studies of the physical processes important to the structure and evolution of stars. He accepted the honour but was upset that the citation named only his earliest work. He saw that as a slight to a lifetime's achievement. Other honours included election as a Fellow of the Royal Society in 1944, the Bruce Medal in 1952 and the Gold Medal of the Royal Astronomical Society in 1953. The National Medal of Science followed in 1966, India's Padma Vibhushan in 1968, and the Copley Medal in 1984.

  NASA named the third of its four Great Observatories after him, following a naming contest that drew 6,000 entries from fifty states and sixty-one countries. Space Shuttle Columbia launched and deployed the Chandra X-ray Observatory on the 23rd of July 1999. A dimensionless number in magnetohydrodynamics, the Chandrasekhar number, also carries his name. So do the asteroid 1958 Chandra and the Himalayan Chandra Telescope. In the Biographical Memoirs of Fellows of the Royal Society, R. J. Tayler wrote: "Chandrasekhar was a classical applied mathematician whose research was primarily applied in astronomy and whose like will probably never be seen again."

  Chandrasekhar died of a heart attack at the University of Chicago Hospital on the 21st of August 1995, at the age of 84. He had survived an earlier heart attack in 1975. Lalitha outlived him and died on the 2nd of September 2013, aged 102. She had given his Nobel Prize money to the University of Chicago, and it funds the Subrahmanyan Chandrasekhar Memorial Fellowship, first awarded in the year 2000. The Association of Asia Pacific Physical Societies began a plasma physics prize in his name in 2014.

  In 2010 the University of Chicago marked his 100th birthday with the Chandrasekhar Centennial Symposium. Roger Penrose, Kip Thorne, Freeman Dyson, Jayant V. Narlikar, Rashid Sunyaev, G. Srinivasan and Clifford Will attended. Its research talks were published in 2011 as the book Fluid flows to Black Holes: A tribute to S Chandrasekhar on his birth centenary. On the 19th of October 2017, a Google Doodle celebrated what would have been his 107th birthday.

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