A Gentle Astrophysical Giant

In 1923, Wilhelm Rontgen died as one of the most celebrated physicists of his time. A modest man, he had declined to take out a patent on his discovery, wanting X-rays to be used for the benefit of humankind. He also refused to name them after himself and donated the money he won from his Nobel Prize to his university.

That same year Subrahmanyan Chandrasekhar started high school in a small town in southern India. Chandra, as he was universally known, would grow into another great but modest scientific fig­ure. Chandra means Moon or luminous in Sanskrit. He was one of nine children and although his family had modest means, they valued education; therefore he was home schooled since local pub­lic schools were inferior and his parents couldn’t afford a private school. His family hoped Chandra would follow his father into government service but he was inspired by science and his mother supported his goal. In addition, he had a notable role model in his uncle, C. U. Raman, who went on to win the Nobel Prize in Physics in 1930 for the discovery of resonant scattering of light by molecules.18

Chandra’s family moved to Madras and he started at the univer­sity there, but was offered a scholarship to study at the University of Cambridge in England, which he accepted. He would never live in India again. At Cambridge he studied, and held his own, with some of the great scholars of the day. As a young man he fell into a controversy with Arthur Eddington, at the time the foremost stellar theorist in the world, which upset him greatly. Eddington refused to accept Chandra’s calculations on how a star might con­tinue to collapse when it had no nuclear reactions to keep it puffed up. Chandra was a gentle man, unfailingly polite and courteous. In part due to this conflict, he chose to accept a position at the Uni­versity of Chicago, where he spent the bulk of his career.

His name is associated with the Chandrasekhar limit, the theo­retical upper bound on the mass of a white dwarf star, or about 1.4 times the Sun’s mass. Above this limit, the force of gravity over­comes all resistance due to inter-particle forces, and a stellar corpse will collapse into an extraordinary dark object, either a neutron star, or if there’s enough mass, a black hole. In the 1970s, he spent several years developing the detailed theory of black holes. Chan­dra was amazingly productive and diverse in his scientific interests. He wrote more than four hundred research papers, and ten books, each on a different topic in astrophysics. For nineteen years, he was the editor-in-chief of The Astrophysical Journal, guiding it from a modest local publication to the international flagship jour­nal in astronomy. He mentored more than fifty graduate students while at the University of Chicago, many of whom went on to be the leaders in their fields. In 1983, he was honored with the Nobel Prize in Physics for his work on the theory of stellar structure and evolution.

Through his long career, Chandra watched the infant field of X-ray astronomy mature. The telescopes flown in sounding rock­ets in the early 1960s were no bigger than Galileo’s spyglass. Just before its 1999 launch, NASA’s Advanced X-Ray Astrophysical Facility was renamed the Chandra X-ray Observatory (CXO) in honor of this giant of twentieth-century astrophysics.19 In a span of less than four decades, Chandra improved on the sensitivity of the early sounding rockets by a factor of 100 million.20 The same sensitivity gain for optical telescopes, from Galileo’s best device to the Hubble Space Telescope, took four hundred years—ten times longer!