Chandrasekhar S
and
His Discoveries
Chandra's Discovery
Chandrasekhar was one of the greatest astrophysicists of the 20th century. He not only discovered the limiting mass for the white dwarfs (now it is known as Chandra limit; more on this in a moment) but also, he mathematically predicted the existence of black holes. The limiting mass puts stars on different paths of evolution to their ultimate complete extinction.
Though Chandra did this work in the early 1930s, his discovery and predictions were unfortunately not pursued; in fact, scientific community ignored them for several decades because of one authoritative astrophysicist who vehemently opposed his discovery.
After the second world war and during the arms race, the developments in nuclear physics, especially in nuclear fusion, and the discovery of the existence of neutron stars, supernovae explosions, and black holes made scientists realize the importance of Chandra’s great discovery.
Eventually, he received the Nobel Prize in 1983 for his work on white dwarfs.
Early Years in India
Chandrasekhar was born in a traditional Tamil Brahmin family in 1910 in British India at Lahore. His father (C. Subramanyan) had joined Indian Civil Service, and he was posted at Lahore as the assistant auditor general for the Northwest Railways when Chandra was born. Chandra’s grandfather, Chandrasekhar Ramanathan, had been a mathematics professor in Visakhapatnam. (A city on the eastern coast and about 400 miles north of Madras.)
His parents were aware that Chandra was exceptionally brilliant, especially in mathematics. The family settled in Madras when Chandra was 13.
Education at Madras
Being exceptionally brilliant and having inspired by Srinivasa Ramanujan (an Indian mathematics genius), Chandra wanted to pursue further study in mathematics. But his father convinced him to choose physics. He studied Physics in Presidency College at Madras (it is Chennai now), India.
At age 19, he published a paper on the quantum properties of a gas of electrons in the Indian Journal of Physics in 1928. And he sent the second paper on this subject to Ralph Fowler of Cambridge University. Fowler helped him publish the paper in Royal Astronomical Society. Subsequently, he decided to continue his graduate studies in Physics at Cambridge, London.
Work at Cambridge
In July 1930, Chandra left Madras for London by ship to continue his graduate studies at the Cambridge University. While on the ship, he started looking into the theory of white dwarf proposed by Fowler whom he was going to work with at the Cambridge University. In 1930s, scientists believed that every star, when they run out of fuel, would implode due to gravity to become white dwarf.
But Chandra, by applying relativistic degeneracy, determined that all white dwarfs thus formed would not be stable. He found a threshold of 1.44 times the solar mass. (The mass of our Sun.) He mathematically predicted that white dwarf with mass greater than that threshold would not be stable and ultimately would collapse to nothing (radius becoming zero).
1935 Paper on White Dwarf
After his Ph.D. at Cambridge, he was accepted as a fellow at Trinity College. He was also working on a formal theory of white dwarf during the fellowship at Trinity. Later, he submitted a formal paper on white dwarf to RAS (Royal Astronomical Society).
In his paper submitted to RAS on January 11, 1935, he stated in the summary that “for a star of small mass the natural white dwarf stage is an initial step towards complete extinction. A star of large mass (greater than the upper limit for white dwarfs) cannot pass into the white dwarf stage, and one left speculating on other possibilities.”
As stated above in the summary, he saw a mass limit. He determined that star-relics of larger mass were not permitted to end their lives in the way everyone at that time believed was standard, as white dwarf. The mass limit is now known as Chandra limit. Only star-relics, having mass less than Chandra limit, would become a white dwarf. Anything greater than that limit would take other paths to their complete extinction.
Though Arthur Eddington, an authority in Astrophysics at that time, opposed Chandra’s theory strongly, Chandra limit prevailed at the end. And Chandra received the Nobel prize in 1983, after almost 50 years, for the discovery he made in 1934.
Neutron Stars & Black Holes
Though Chandra’s theory was not accepted in 1930s, later, after many decades, Chandra’s discovery was found to be correct. The developments in later decades and the discovery of neutron stars, supernovae and black holes vindicated that Chandra’s discovery was right and Eddington was wrong.
Also, astronomers observed that all the stable white dwarfs were found to have masses less than Chandra limit and that star-relics with mass greater than Chandra limit either becoming a neutron star after supernova explosion or (the bigger ones) becoming a black hole.
Chandra X-Ray Observatory
In 1999, after 4 years of Chandra’s death, NASA’s space shuttle Columbia lifted off from Florida and placed an X-ray observatory in Earth’s orbit. It was aptly named Chandra X-ray observatory.
The mission of the Chandra’s X-ray observatory was to study black holes.
Sources:
- Ideal Scholar Subramanyan Chandrasekhar, Great Physicists by William H Cropper, Oxford University Press
- Empire of the stars: obsession, friendship, and betrayal in the quest for black holes / Arthur I. Miller