Thursday, September 23, 2021

Subrahmanyan Chandrasekhar: The man who reshaped Astrophysics in the 20th century

He received the Nobel Prize in Physics (1983) alongside William A. Fowler for his theoretical studies of the physical processes of importance to the structure and evolution of the stars. The Chandrasekhar limit is also named after him. The concept gives the maximum mass of a stable white dwarf star. When a star like our Sun exhausts its nuclear fuel, it collapses into a compact, brilliant star known as a white dwarf.

“Science is a perception of the world around us. Science is a place where what you find in nature pleases you,” these are the words of Subrahmanyan Chandrasekhar. The man who helped the world better understand one of the largest stellar bodies- Stars, and what happens when they collapse or run out of fuel. 

He received the Nobel Prize in Physics (1983) alongside William A. Fowler for his theoretical studies of the physical processes of importance to the structure and evolution of the stars. The Chandrasekhar limit is also named after him. The concept gives the maximum mass of a stable white dwarf star. When a star like our Sun exhausts its nuclear fuel, it collapses into a compact, brilliant star known as a white dwarf.

In the early 1930s, S. Chandrasekhar formulated theories for stars’ different development when they ran out of fuel. Stars are basically powered by Nuclear fusion for most of their existence. Hydrogen atoms act as the primary fuel for a star. Chandrasekhar showed that when the hydrogen fuel of stars of a certain size begins to exhaust, it collapses into a white dwarf.

21 August is the death anniversary of the legendary astrophysicist, Subrahmanyan Chandrasekhar. And we will dwell deep in his contributions to the Humankind and Science that he has made in his lifespan. 

Subrahmanyan Chandrasekhar’s early life 

The boy with curiosity was born in Lahore (now in Pakistan) on the 19th of October 1910. He was the first son and the third child of Chandrasekhara Subrahmanya Ayyar (Father) and Sita (Mother). His father was an officer in Government Service in the Indian Audits and Accounts Department. 

Till twelve, Subrahmanyan received his education at home from his parents and by private tuition.  In 1918, Subrahmanyan Chandrasekhar’s father was transferred to Madras. 

Education

In Madras, Subrahmanyan attended the Hindu High School, Triplicane (1922-25). Further for the university education, he moved to the Presidency College during the years 1925-30.

In Madras, he went to the Hindu High School, Triplicane, during the years 1922-25. His university education (1925-30) was at the Presidency College.  He completed his bachelor’s degree, B.Sc. (Hon.), in physics in June 1930.

In the same year, he was awarded a Government of India scholarship for graduate studies in Cambridge, England. There, Subrahmanyan was a research student under the supervision of Professor R.H. Fowler.

Chandrasekhar limit

In astrophysics, the Chandrasekhar limit is the maximum mass theoretically feasible for a stable white dwarf star. When a star like our Sun exhausts its nuclear fuel, it collapses into a compact, brilliant star known as a white dwarf.

By the early 1930s, several scientists had reached the conclusion that stars after converting all of their hydrogen to helium exhaust their energy and contract under the influence of their own gravity. Chandrasekhar determined what is known as the Chandrasekhar limit. He came up with the idea for a limit on his voyage to England in 1930.

The stars contracted about the size of Earth are known as white dwarf stars. Chandrasekhar used Albert Einstein’s special theory of relativity and the principles of quantum physics to show that it is impossible for a white dwarf star to be stable if its mass is greater than 1.44 times the mass of the Sun. The currently accepted value of the Chandrasekhar limit is about 1.4 M (Mass of Sun) (2.765×1030 kg).

The limit means that a star having a mass more than 1.44 times that of our Sun does not evolve in a white dwarf. The star keeps on collapsing and blows off its gaseous envelope in a supernova explosion, and becomes a neutron star. A more massive star further continues to collapse and becomes a black hole.

Chandrasekhar’s calculations bestowed the eventual understanding of supernovas, neutron stars, and black holes. Chandrasekhar came up with the idea for a limit on his voyage to England in 1930. However, his ideas met strong resistance from English astronomer Arthur Eddington and the idea took years to be generally accepted in the science community.

NASA’s Chandra X-ray Observatory

NASA’s premier X-ray observatory was named in honor of the Subrahmanyan Chandrasekhar as the Chandra X-ray Observatory. The Observatory was launched and deployed by Space Shuttle Columbia on 23 July 1999. The observatory is the most sophisticated X-ray observatory built to date. Chandra is designed to detect X-rays from high-energy regions of the universe, such as the residues of exploded stars.  

Subrahmanyan Chandrasekhar’s Contribution to Science 

Subrahmanyan Chandrasekhar, known to the world as Chandra (which means “moon” or “luminous” in Sanskrit), was widely regarded as one of the foremost astrophysicists of the 20th century. Like his name, he illuminated several physics concepts to the world, including stellar structures, including the theory of white dwarfs (1929-1939), and stellar dynamics, including the theory of Brownian motion (1938-1943). 

The concepts also consist of the theory of radiative transfer, including the theory of stellar atmospheres and the quantum theory of the negative ion of hydrogen. And the theory of planetary atmospheres, including the theory of the illumination and the polarization of the sunlit sky (1943-1950).

He also worked on other topics like the theory of the Rayleigh-Bénard convection, the general theory of relativity & relativistic astrophysics, the mathematical theory of black holes (1974- 1983), and several others. The famous monographs from Subrahmanyan are listed below: 

  1. An Introduction to the Study of Stellar Structure (1939, University of Chicago Press; reprinted by Dover Publications, Inc., 1967).

2a. Principles of Stellar Dynamics (1943, University of Chicago Press; reprinted by Dover Publications, Inc., 1960).

2b. ‘Stochastic Problems in Physics and Astronomy’, Reviews of Modern Physics, 15, 1 – 89 (1943); reprinted in Selected Papers on Noise and Stochastic Processes by Nelson Wax, Dover Publications, Inc., 1954.

  1. Radiative Transfer (1950, Clarendon Press, Oxford; reprinted by Dover Publications, Inc., 1960).
  2. Hydrodynamic and Hydromagnetic Stability (1961, Clarendon Press, Oxford; reprinted by Dover Publications, Inc., 1981).
  3. Ellipsoidal Figures of Equilibrium (1968; Yale University Press).
  4. The Mathematical Theory of Black Holes (1983, Clarendon Press, Oxford).

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