Our current understanding of the evolutionary stages of massive stars, including black holes, is the result of an extensive theoretical work of an Indian–American scientist, Subrahmanyan Chandrasekhar, better known as Chandra. In honor of this prodigy discoverer of the universe, Chandra’s name was bestowed upon NASA’s premier X-ray observatory: the Chandra X-ray Observatory.
In 1983, Chandrasekhar was awarded the Nobel Prize in Physics for the mathematical theory he formulated to explain the physical processes of the birth, structure, development, and evolution of stars. It is believed that he carried out this work when he was just 19 years old, on a ship traveling from India to Britain to begin working on a PhD in Physics. This is the youngest age at which Nobel Prize winning work was awarded.
Subrahmanyan Chandrasekhar was born on 19 October 1910, in the city of Lahore. He was the nephew of Sir Chandrasekhara Venkata Raman, who won the Nobel Prize in Physics in 1930 after carrying out groundbreaking work in the field of light scattering.
Born to a well-educated family, as a child, Chandra was home-schooled by private tutors until 1921, when he enrolled in a Hindu High School, where he excelled. Later on, Chandra studied at Presidency College in Madras; upon graduating with a Master’s degree in 1930, he set off for Trinity College, Cambridge. Although he won the Nobel Prize for the work he did at an early age, Chandrasekhar performed throughout his scientific life extensive research that covered many other areas within theoretical physics and astrophysics.
To form an idea about the significance of the contribution Chandrasekhar made in the field of astronomy, one needs to learn about the common understanding of the stars evolution at that time. By the early 1930s, scientists had concluded that, after converting all of their hydrogen to helium, stars lose energy and contract under the influence of their own gravity. These stars, known as white dwarf stars, contract to about the size of Earth, and the electrons and nuclei of their constituent atoms are compressed to a state of extremely high density.
Chandrasekhar determined what is known as the Chandrasekhar limit. He proved that a star having a mass more than 1.44 times that of the Sun does not form a white dwarf, but instead continues to collapse, blowing off its gaseous envelope in a supernova explosion, and becoming a neutron star; an even more massive star continues to collapse and becomes a black hole. These calculations contributed to the eventual understanding of supernovas, neutron stars, and black holes.
A supernova is an explosion of a massive supergiant star; it may shine with the brightness of ten billion Suns. The total energy output may be as much as the total output of the Sun during its ten-billion year lifetime. A neutron star, on the other hand, is a type of compact star; neutron stars are the smallest and densest stars known to exist in the Universe. With a radius of only about 11–11.5 km, they can have a mass of about twice that of the Sun; they can result from the gravitational collapse of a massive star after a supernova. Finally, a black hole is a region of space and time exhibiting such strong gravitational effects that nothing, including particles and electromagnetic radiation such as light, can escape it.
Chandrasekhar proved that, as stars evolve, they release energy generated by their conversion of hydrogen into helium and even heavier elements. As they reach the end of their life, stars have less hydrogen left to convert so they release less energy in the form of radiation. They eventually reach a stage when they are no longer able to generate the pressure needed to maintain their size against their own gravitational pull, and they begin to shrink, eventually collapsing into themselves. Their electrons become so tightly packed that their normal activity is shut down and they become white dwarfs, or tiny objects of enormous density.
Chandrasekhar became an American citizen in 1953. He retired from the University of Chicago in 1980, but remained on as a post-retirement researcher. In 1983, he published a classic work on the mathematical theory of black holes. Chandra passed away in Chicago on 21 August 1995, at the age of 82. Throughout his life, Chandrasekhar strove to acquire knowledge and understanding; according to an autobiographical essay published with his Nobel lecture, he was motivated “principally by a quest after perspectives”.
References
www.britannica.com
www.notablebiographies.com
www.physicsoftheuniverse.com
Banner image