In 1928 an Indian graduate student named subrahmanyan Chandrasekhar set sail for england to study at cambridge with the british astronomer Sir Arthur Eddington.Eddington was an expert on general relativity.

           During his voyage to india,Chandrasekhar worked on how big a star could be and still separate itself under it's own gravity after it had used up all it's fuel.The idea was this: when the star becomes small, the matter particles get very near to each other.But the pauli exclusion principle says that two matter particles can't have both the same position and the same velocity.The matter particles must therefore have very different velocities.

This makes them move away from each other,and so tends to make the star expand. A star can therefore maintain itself at a constant radius by a balance between the attraction of gravity and the repulsion that arises from the exclusion principle, just as earlier in it's life the gravity was balanced by the heat.

           Chandrasekhar realized, however, that there is a limit to the repulsion that the exclusion principle can provide.The theory of relativity limits the max difference in the velocities of the matter particles in the star to the speed of light. That meant that when the star got sufficiently dense, the repulsion caused by the exclusion principle would be less than the attraction of gravity.Chandrasekhar calculated that a cold star of more than one and a half times the mass of the sun wouldn't be able to support itself against it's own gravity. This mass is now known as the "CHANDRASEKHAR LIMIT".  

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