Subramaniam Chandrashekhar

Subramanian Chandrashekhar

Subramanian Chandrashekhar

Subramaniam Chandrashekhar was born on October 19, 1910 in Lahore, India ( later part of Pakistan ). At the time of Chandrashekhar’s birth, his father, Chandrashekhar Subramaniam Ayyar, was an officer in the Department of Audits and Accounts of Indian Government Services. He was the third of ten children ( four sons and six daughters, Chandrashekhar was the first son). Chandrashekhar’s mother, Sita Balakrishnan, was a devoted to her children and instilled in them a sense of great ambition from an early age. Chandrashekhar received his elementary education from his parents and private tutors when he was in Lahore. In 1918 his father was transferred to Madras ( renamed Chennai recently ) where the family made their permanent home. In Madras, Chandrashekhar attended the Hindu High School from 1922 to 1925 where he finished his secondary school education with honors. He then attend Presidency College from 1925 to 1930, following in the footsteps of his famous uncle, Sir C. V. Raman, discoverer of Raman effect and the Nobel laureate in physics for the year 1930. He received his bachelor of science degree (in physics), with honors, in1930. Because of his academic achievements, Chandrashekhar was awarded a scholarship by the government of India to attend graduate school at the University of Cambridge, England. At Cambridge he became a research student of R. H. Fowler and got his doctorate in 1933. During this time he spent a year studying at the Institut for Teorestik Fysik, in Copenhagen, Denmark.

Soon after receiving his doctorate, Chandrashekhar was awarded the Prize Fellowship at Trinity College, Cambridge. He stayed in this position until 1937. During this time Chandrashekhar married Lalitha Doriswamy, whom he had met in college, in September of 1936. While at Trinity, Chandrashekhar met and formed lasting friendships with prominent astrophysicists including Sir Arthur Eddington and E. A. Milne. During his tenure at Trinity, he presented two papers to the Royal Astronomical Society. One of these presentations dealt with the theory of white dwarf stars and how the quantum mechanical properties of the electron dictate the behavior of these stars at the end of their life cycle. Chandrashekhar’s colleague Eddington followed this paper with a presentation that was very critical of Chandrashekhar’s results. This attack was severe blow to Chandrashekhar’s feeling and left a life long impression on him. As a result of the disagreement and the stature of Sir Arthur Eddington, Chandrashekhar realized that his chances of obtaining a tenured position at a British university were slim at best. Therefore, in 1937, while visiting at Harvard University, he accepted a position as a research associate at the University of Chicago offered to him by the famous American astronomer Otto Struve. Chandrashekhar stayed at University of Chicago through out his career. He was named to the faculty as assistant professor in 1938. He was promoted to associate professor in 1942 and to full professor in 1944. He became the Distinguished Service Professor of Theoretical Astrophysics in 1947. Because of earlier disappointing experience with Eddington, Chandrashekhar repeatedly showed his respect for the ideas and work of his colleagues as well as his students. His dedication to the students is well known. Two of Chandrashekhar’s students in 1947 were the doctoral candidates Tsung-Dao Lee and Chen Ning Yang from China. Even though he maintained his office at the Yerkes Observatory In Lake Geneva, Wisconsin, he would regularly drive the one hundred miles to Chicago to instruct Lee and Yang. In 1957, these two students won the Nobel prize in Physics for their work in particle physics research.

Chandrashekhar began his formal scientific training at Presidency College in Madras, India. From the beginning, he was interested in astrophysics and kept abreast of the latest developments. The work of astrophysicists Sir Arthur Eddington and Ralph Fowler on stellar evolution, or cyclesof stars, was especially of interest to him. In 1930, after obtaining his bachelors of science degree from Presidency College, Chandrashekhar entered Trinity College at the University of Cambridge, England. At about the same time he entered and won a physics competition and was rewarded with a copy of Eddington’s book ” The Internal Constitution of Stars”. Chandrashekhar studied the book at great length, leaving no detail unexamined. This process was a mark of his lifelong habits in doing science: thoroughness, persistence, and precise mathematical rigor. In the book, Eddington maintained that all stars collapsed into dense Earth-sized objects after spending their fuel supplies. This configuration of star of a star at the end of its life cycle is known as white dwarf. Chandrashekhar found some weakness in Eddington’s arguments about all stars becoming white dwarfs. Eddington’s arguments were somewhat qualitative and did not include the results of special relativity and quantum physics. After applying quantum physics and relativity to Eddington’s calculations, Chandrashekhar concluded that only stars of modest or low mass could become white dwarfs but not the massive stars. The calculations showed that stars with masses greater than 1.44 times mass of our own Sun would contract beyond the Earth-size like white dwarf to a point of even smaller sizes. This upper limit of 1.44 time the mass of the Sun on white dwarfs is now known as Chandrashekhar limit. By 1933, Chandrashekhar formed a complete theory of white dwarfs and decided to report the results at a meeting of the Royal Astronomical Society . After submitting the paper and shortly before the meeting, he received a copy of the program. To his surprise Chandrashekhar found that Sir Arthur Eddington is scheduled to present a paper on the same subject, immediately following his. Even though Eddington and Chandrashekhar had been working together and meeting regularly, Eddington had never said anything about submitting a paper. Even more surprising was the fact that Eddington did not say that he was working on the same material. In his presentation, Chandrashekhar argued that the life cycles of high mass stars (stars above the Chandrashekhar limit) “must be essentially different” from those of the stars below the Chandrashekhar limit. From his results, he indicated how the high mass stars might behave towards the end of their life cycle. This logic clearly pointed towards the eventual discovery of such phenomena as neutron stars and black holes; the latter are so massive and so compressed that even electromagnetic radiation can not escape the powerful gravitational pull of the star. Eddington’s presentation following this talk was highly critical of Chandrashekhar’s entire theory. He specifically attacked the use of relativistic results and proposed that there must exist in nature a phenomenon that would prevent the powerful gravitational pull that exists towards the end of the life cycle of high mass stars. This attack by his colleague and a well respected astrophysicist of the day had a life long effect on Chandrashekhar. After recovering from the shock of this attack, Chandrashekhar examined his work carefully and decided that he was on the right track in spite of Eddington’s criticisms. He realized that the argument between him and Eddington was essentially in what kind of physics to apply to these compressing stars at end of their life cycle. Prominent physicists like Niels Bohr and Wolfgang Pauli assured Chandrashekhar privately that he was on the right track and encouraged him. But few scientists were willing to challenge publicly the authority of Sir Arthur Eddington. As a result of his ongoing disagreement with Eddington, Chandrashekhar accepted a position at the University of Chicago in 1937, while visiting Harvard University. He stayed at the University of Chicago for the rest of professional career. At this point Chandrashekhar started investigating an entirely different area of research, the dynamics of star clusters (the detailed motion of stars in clusters). After his usual through work, he determined that star cluster dynamics were similar in nature to the Brownian motion of particles suspended in liquids. From this research he estimated the time it would take for the clusters to have attained the present state of motion. After many years of work, he published a definitive work, The principles of Stellar Dynamics (1942). This pattern of working on a particular subject until_publishing a definitive work and moving on to another subject became the hallmark of Chandrashekhar’s career.

During World War II, Chandrashekhar was called on to work on the top – secret atomic weapons research going on at the University of Chicago. During these years, he collaborated with prominent physicists like Enrico Fermi and James Frank. These physicists later joined the physics department at the university, adding to its reputation as one of the leading centers in physics in the United States. As a result, many outstanding graduate students flocked to the physics department. Two of these students were Tsung-Dao Lee and Chen Ning Yang who worked with Chandrashekhar. Dedication that Chandrashekhar showed to these two students would become pattern through out his_career. These two students won the Nobel Prize in 1957, for their work in particle physics. Towards the late 1940’s, Chandrashekhar started his studies on the radiative transfer in the interior of stars: the specifics of how light energy moves and interacts with the material through which it travels. Soon after that, he began to study the effects of magnetism on galaxies, including the Milky Way, with special interest on how magnetic field effects the shapes of galaxies. Following his earlier pattern, he published a book, Hydrodynamics and Hydromagmnetic Stability (1961). From 1961 to 1968, Chandrashekhar studied equilibrium of ellipsoidal figures : the study of oblate spheres (spheres that bulge at the equator), and prolate spheres (spheres elongated like footballs). This work provided him with the understanding of the rotation of planets, stars, white dwarfs, neutron stars, black holes, galaxies, and clusters of galaxies. After the completion of this study, he published a book, Ellipsoidal Figures of Equilibrium in 1969. In the mid 1970’s, Chandrashekhar went back to the study of collapsing stars to understand a nagging detail that had been at the back of his mind. In his famous presentation to the Royal Astronomical Society in 1933, he had stopped short of talking about a complete gravitational collapse of high mass stars, but a such a possibility had already occurred to him. To understand this possibility he concentrated his studies on the general theory of relativity and relativistic astrophysics. This work lead to his monumental publication of The Mathematical Theory of Black Holes in 1983.

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