Subrahmanyan Chandrasekhar

Astrophysicist

• Born: October 19, 1910
• Birthplace: Lahore, India
• Died: August 21, 1995
• Place of death: Chicago, Illinois

Indian American astrophysicist

Twentieth-century Indian American astrophysicist Subrahmanyan Chandrasekhar studied the evolution of stars throughout their life spans. Chandrasekhar predicted which stars would become white dwarfs and determined that larger stars would eventually collapse into small areas of extreme gravity called black holes.

Born: October 19, 1910; Lahore, British India (now Pakistan)

Died: August 21, 1995; Chicago, Illinois

Primary field: Physics

Specialties: Astrophysics; theoretical physics; theoretical astronomy

Early Life

Subrahmanyan Chandrasekhar (shahn-druh-SEY-kahr) was born on October 19, 1910, in Lahore, British India (now Pakistan). Popularly known as Chandra among scientists, he was one of ten children born to Chandrasekhara Subrahmanya Ayyar and his wife, Sita Balakrishnan. Ayyar was an Indian government auditor, and Balakrishnan translated literary works into the Tamil Indian dialect. Chandra’s uncle was physicist Chandrasekhara Venkata Raman, winner of the 1930 Nobel Prize in Physics for his work on the scattering of light.

As a child, Chandrasekhar was educated at home, but he began attending high school when his family relocated to Madras, in southeastern India. After graduating high school in 1925, he entered Presidency College in Chennai, India. He was awarded a bachelor’s degree in physics in 1930 and won a scholarship to study at the University of Cambridge in England beginning that year.

At Cambridge, Chandrasekhar worked in the laboratory of physicist Ralph H. Fowler. In his third year, he spent time abroad studying at the Nordic Institute for Theoretical Physics in Copenhagen, Denmark. He earned his doctorate from Cambridge in 1933 and was awarded a fellowship for postdoctoral work at the university’s Trinity College.

During the early years of his career, Chandrasekhar hoped to obtain a teaching position at Cambridge, but an inadvertent conflict with British astrophysicist Arthur Eddington prevented him from doing so. Instead, in 1936, Chandrasekhar briefly returned to India to marry Lalitha Doraiswamy, whom he had originally met at Presidency College. When Chandrasekhar was offered a research associate position at the University of Chicago in Illinois, he accepted, and in late 1936, he and his wife moved to the United States. The following January, Chandrasekhar joined the Yerkes Observatory, a facility of the university’s astronomy and astrophysics department in Williams Bay, Wisconsin.

Life’s Work

Eddington and Chandrasekhar were both researching the same subject: the life cycle of stars. Some old stars become white dwarfs when they begin to run out of fuel. White dwarf stars are relatively dim, but they are among the densest substances known. They contain half the mass of the sun compressed into a space not much larger than the Earth. The inner part of the star becomes hotter and denser as its hydrogen fuel runs low. This blasts gaseous outer material from the surface of the star. Once the outer material of the star is gone, the hot inner core warms the ejected gases, making them glow in a variety of colors. These glowing gases are called planetary nebulae.

Eddington believed that, eventually, all stars become white dwarfs. He had devoted much of his research to proving this and was not open to new ideas. Chandrasekhar approached the problem differently. He utilized his knowledge of theoretical physics, integrating concepts of special relativity into his calculations. His equations indicated that Eddington was incorrect. Only stars no greater than 1.4 times the mass of the sun would end as white dwarfs. He predicted that stars much larger than the sun would end by exploding and leaving behind cores that could collapse into extremely high areas of gravity. He presented these findings to the Royal Astronomical Society in 1935.

Eddington was scheduled to speak directly after Chandrasekhar. Upon taking the stage, he ridiculed Chandrasekhar’s findings. Privately, many distinguished physicists agreed with Chandrasekhar, but Eddington was too politically powerful to be confronted openly. Due to the conflict with Eddington, Chandrasekhar left England and spent the next part of his career at the University of Chicago and the nearby Yerkes Observatory. He was interested in a variety of topics and wrote prolifically. The results of his studies on the evolution of stars were summarized in the book An Introduction to the Study of Stellar Structure, published in 1939. He would continue his work on stellar interiors into the 1950s.

Chandrasekhar’s career at the university was interrupted during World War II by his work at the Ballistic Research Laboratory at the Aberdeen Proving Ground in Maryland. During the war, Chandrasekhar conducted research on the reflection of blast waves and the properties of aircraft shock waves. He also worked on a secret atomic weapons project at the University of Chicago.

In 1943, Chandrasekhar published Principles of Stellar Dynamics, a mathematical exploration of the distribution and motion of stars and galaxies. In this work, he applies classical dynamics, based on Isaac Newton’s laws of motion, to the movement of star clusters. His analysis of the gravitational attraction on a single star moving past a star cluster provided clues to the ages of the clusters.

Chandrasekhar and Eddington eventually reconciled. With Eddington’s support, Chandrasekhar was elected to the Royal Society of London in 1944. In 1952, Chandrasekhar began editing the Astrophysical Journal. Under his leadership, which lasted until 1971, the journal grew from a small local publication to a prestigious international journal. The University of Cambridge invited Chandrasekhar back as faculty in 1964, but by that time he was comfortable in Chicago and declined. He and his wife had also become American citizens in 1953, and Chandrasekhar chose to remain at the University of Chicago for the remainder of his career.

Approximately fifty years after Chandrasekhar presented his findings about evolution of stars, the Nobel Prize Committee honored him with the 1983 Nobel Prize in Physics. A prolific researcher, Chandrasekhar authored many books and hundreds of scientific papers during his career, including one of his most significant works, The Mathematical Theory of Black Holes, published in 1983. His last book was published in 1995, when Chandrasekhar was eighty-four, just a few months before his death. Chandrasekhar died of heart failure on August 21, 1995, in Chicago.

Impact

During Chandrasekhar’s teaching career, more than fifty students obtained their doctorates in his laboratory. Two of his best-known students, Tsung-Dao Lee and Chen Ning Yang, were awarded the 1957 Nobel Prize in Physics for their research into particle physics.

Chandrasekhar’s theories went unrecognized for decades. The astrophysicist blamed this on Eddington’s original opposition, but there was also a lack of evidence to support Chandrasekhar’s mathematical claims. Even by the time The Mathematical Theory of Black Holes was published, little evidence had been found to support Chandrasekhar’s calculations. Evidence has since been obtained, however, and Chandrasekhar’s theories have been widely accepted.

Through further studies of the stars, astrophysicists have been able to prove Chandrasekhar’s predictions about what occurs at the end of a star’s life. The mass of a star affects when it runs low on fuel. Stars that are 1.4 times the mass of the sun or less—the “Chandrasekhar limit”—can become white dwarfs. Stars much larger than the sun may end their lives in spectacular explosions called supernovae. These explosions leave behind superdense cores called neutron stars, which, as Chandrasekhar predicted, can collapse into areas of extremely high gravity. Astrophysicists later called the high-gravity areas black holes, because not even light can escape their gravitational pull.

Bibliography

Chandrasekhar, Subrahmanyan. The Mathematical Theory of Black Holes. New York: Oxford UP, 1998. Print. A reprint of Chandrasekhar’s 1983 book on relativity theory in relation to the existence of black holes. Tables, bibliography, index.

---. A Scientific Autobiography: S. Chandrasekhar. Ed. Kameshwar C. Wali. Hackensack, NJ: World Scientific, 2010. Print. An autobiography of Chandrasekhar’s life and work, edited and published posthumously.

LeBlanc, Francis. An Introduction to Stellar Astrophysics. Chichester, UK: Wiley, 2010. Print. Explains the structure and functioning of the stars as understood through physics concepts and observations. Illustrations, appendixes, bibliography, index.

Prialnik, Dina. An Introduction to the Theory of Stellar Structure and Evolution. 2nd ed. Cambridge: Cambridge UP, 2010. Print. Covers the structure, processes, and life cycles of different types of stars. Illustrations, appendixes, bibliography, index.