Q.What is the contribution of S. Chandrasekhar to Physics?

Chandrasekhar's key contribution is the Chandrasekhar limit, which determines the fate of dying stars and founded modern stellar-evolution theory.

A star spends most of its life fusing hydrogen into helium, with the outward thermal/radiation pressure of fusion balancing the inward pull of gravity. When a star like the Sun exhausts its nuclear fuel, it collapses into a very dense remnant called a white dwarf, where further collapse is halted not by fusion but by electron degeneracy pressure — a quantum-mechanical effect (from the Pauli exclusion principle) that resists compressing electrons too closely together.

S. Chandrasekhar showed, using special relativity combined with quantum statistics, that this electron degeneracy pressure can only support a white dwarf up to a maximum mass of about 1.4 times the mass of the Sun — now called the Chandrasekhar limit.

• A star whose core mass is below this limit ends its life peacefully as a stable white dwarf.
• A star whose core mass exceeds this limit cannot be held up by electron degeneracy pressure alone; it continues to collapse, ultimately becoming a neutron star or, for still more massive cores, a black hole. …