Subrahmanyan Chandrasekhar: Discovery, Inventions & Contributions

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Subrahmanyan Chandrasekhar (1910-1995) was one of the twentieth century's greatest astronomers. He conducted research in many different fields of astronomy and wrote a number of popular books. In this lesson, learn all about him and his discoveries!

How Big Can a Star Grow?

We all know that stars are really, really big, but is there a limit to HOW big a star can grow? This was a question that puzzled astronomers for many years. It seemed that some stars could be very large without collapsing, while others would explode into giant supernovas and then collapse and turn into black holes or small, dense neutron stars. What was the difference? Why did some stars collapse and others didn't?

When a star grows very large, it will explode into a supernova like this one. After the supernova, a small, dense, neutron star is left at the center.
Supernova remnants with neutron star in the center

In the 1930's, a young Indian astronomer named Subrahmanyan Chandrasekhar, working at Cambridge University, finally answered this question. He found that stars that were bigger than about 1.4 times the mass of our sun would ultimately collapse, while those with smaller masses would not. Although this discovery was not particularly popular among physicists and astronomers at the time, over time it has been proven to be accurate. This critical mass is now known as the Chandrasekhar limit.

Did Chandrasekhar discover the Chandrasekhar limit after a lifetime of studying the stars? No, he published his most famous discovery when he was only 21 years old! This was just the beginning of his long and very productive career as an astronomer.

Early Life

Subrahmanyan Chandrasekhar was born in 1910 in a region of India that is now part of Pakistan. It was obvious very early in his life that he was very intelligent. His parents taught him at home when he was a small child, and then later he attended Hindu High School in Madras. He graduated from high school in 1925 at the age of 15 and immediately enrolled in the University of Madras. While at the university, he continued to excel. He graduated in 1930 with a Bachelor of Science degree, and because of his academic success while in college, he was awarded a fellowship from the government of India to pursue graduate studies at Cambridge University in England.

Contributions to Astronomy

Chandrasekhar began making his mark in the scientific world as soon as he arrived in Cambridge. In a series of papers he wrote and published between 1931 and 1935, he clearly laid out his evidence for the existence of the Chandrasekhar limit. His work was very controversial at the time, and famous scientists like Albert Einstein and Arthur Eddington publicly spoke out against his research.

In the midst of all this controversy, he finished his Ph.D. in 1935 and continued to work at Cambridge as a fellow for a few more years. He had hoped to stay in England and become a professor at a British university, but because of the opposition he faced he was afraid that would never happen.

In 1937, he was offered a job in the United States instead, and he jumped at the opportunity to leave Cambridge behind. He began working as an assistant professor of astrophysics at the University of Chicago in 1938 and remained there for the rest of his career, becoming an American citizen in 1953.

Books by Chandrasekhar

Chandrasekhar's research interests were wide ranging, and he made many significant contributions to various fields of astronomy in his long career. He was a prolific writer, who published a number of popular books on his research. Many of his books are still in print today.

Early in his career, when he was still working in Cambridge, Chandrasekhar primarily studied the structure of stars. It was during this time that he discovered the Chandrasekhar limit, which would be his most famous contribution to astronomy. In 1939, he published his first book, An Introduction to Stellar Structure, which detailed much of the work that he did during this period.

After relocating to the University of Chicago, he changed the focus of his research slightly and began studying stellar dynamics, which is a branch of astronomy that studies the motion of groups of stars, like those found in galaxies or star clusters. He worked on this from about 1939-1943, and published another book, Principles of Stellar Dynamics, in 1942.

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