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Let us see how Subrahmanyan Chandrasekhar, fondly called Chandra, wrote the Jataka of Stars.

Life of a star. A typical star like our sun has various layers. The core is the central region where nuclear fusion happens. A hydrogen atom is converted to Helium through fusion, thereby steadily releasing an enormous amount of energy.  Energy moves out from the radiation zone as radiation. In the convective zone, hot gas rises and cold gas sinks like boiling water. The photosphere is the visible surface that emits light. Corona is the thin, hot outer atmosphere visible in a solar eclipse. The life of a star is fundamentally a battle between two forces: the inward pull of gravity and the outward pressure generated by nuclear fusion. The star will spend almost ninety percent of its lifetime in this stage.

Chandra was born on 19.10.1910 in Lahore in a Tamil family. His parents are C Subramanyan and Sitalakshmi Balakrishnan. He studied at Presidency College, Madras, and earned his BSc in Physics in 1930. He got a Government of India scholarship to study at Trinity College, Cambridge, and completed his PHD in 1933. After Cambridge, he moved to the University of Chicago and spent most of his life in Chicago, and became a US citizen in 1953. He died on 21.08.95

In the first part of this essay, we have seen how the stars are born. Let us now discuss the life and death of stars. A star spends its active lifetime by continuously burning and converting its hydrogen fuel inside the star to Helium through nuclear fusion. This is a stable phase, and no other major events happen inside the star during this phase. The next phase of the star, that is, its end, starts when the fuel for its nuclear fusion is exhausted after millions of years of burning. The duration of its active life depends on its mass. Massive stars burn faster. Low-mass stars like our sun live for billions of years.

 It is Chandra who theorized how the different stars come to their end phase. Chandra arrived at his equations of limiting mass from combining Quantum mechanics and Special relativity. That is from electron degeneracy pressure, as defined in the Pauli exclusion principle (how tightly electrons could be packed), and velocities of matter approaching the speed of light as per special relativity.

 It all happened in Chandra’s journey on the steamer after winning a government scholarship to study in Cambridge under Sir Arthur Eddington.  Edington’s reputation was such that, in those days, scientists believed that the only other person who understood relativity other than its author, Einstein, was Eddington.

Chandra, just 19 years of age, shy and introspective, departed from the shores of Madras aboard the ship S.S. Pilsna in 1930, setting his face toward the west, so that he could learn the secrets of the heavens. Though his body journeyed upon the waters, his thoughts journeyed among the stars. He carried with him notebooks and a set of papers written by the renowned scientists Ralph Fowler and Eddington. Even as the steamer swayed on the waves, he sat working on the papers, aloof, while the other passengers made merry.  The winds were his companion, and his solace was the whisper of the sea.

He asked himself, What is the end of a star when its fire is spent. By that time, after studying the work of Fowler in detail, Chandra realized that Ralph Fowler’s work was incomplete. He joined the words of Einstein to the law of Pauli, and then both to the dust of creation to get an answer. He used the entire voyage working out the mathematics of electron degeneracy under relativistic (very fast) conditions. This led Chandrasekhar to his theory of the evolution of Stars.

 By the end of his voyage, Chandra realized the great truth that, as electrons become very fast, their ability to resist gravity weakens, thus setting limits on the mass of stars, to gain stability.

The decree of heaven was revealed to him, that the proud star, if too great (massive), must perish faster, and only the meek shall be stable for a longer time. Once the hydrogen fuel is completely burned off, the core of the star, due to its own gravity, collapses into a very dense state, and its outer layers explode as a supernova and are blown off. The dense core of the star is converted into a white dwarf, a neutron star, or a Black hole, depending on the star’s initial mass.

  Supernova

His studies showed that the maximum initial mass a star can have is 1.44 times the mass of the sun, to remain stable as a white dwarf. That means a star that has an initial mass of less than 1.44 times the mass of the Sun gets converted to a stable white dwarf at the end of its life span. A white dwarf will have a radius of only a few thousand miles, but it will have a high density that a cubic inch of its matter will weigh hundreds of tons.

 A star with an initial mass up to two to three times the mass of the Sun will get converted to a still smaller neutron star with even more density.

Stars still heavier shall get converted to a blackhole at the end of their lives. (A black hole is not a physical hole in space. It is a region where matter is compressed at extremely high density. The gravity in that region is so high that nothing can escape from that region, not even light rays. So it appears dark.)

By the time he landed in England, his equations were ready to support his theory. But the wise men of the land called his vision folly and mocked him before the multitude. Eddington called it a stellar buffoonery.

But Chandra was not moved and held his peace. In the fullness of time, the truth that was sown in the solitude of the mighty ocean brought forth the fruit of Glory.

Chandra won the Nobel Prize in 1983 for his theory, popularly known as the Chandrasekhar limit.

Audio Credit: movie Krrish 3, Flute melody