1. A mass limit for the isothermal, helium core of a main-sequence star above which the star must rapidly increase in radius and evolve away from the main sequence.
2. A limit on the mass of a main sequence star's core above which the star will leave the Main Sequence to become a red giant.

This takes place when the helium core makes up 10 to 15 per cent of he star's mass.

3. The maximum mass of a star's helium-filled core that can support the overlying layers against gravitational collapse, once the core hydrogen is exhausted; it is believed to be 10 to 15% of the total stellar mass.

If this limit is exceeded, as can only happen in massive stars, the core collapses, releasing energy that causes the outer layers of the star to expand to become a red giant.

It is named after Indian-born (Lahore, India, now Pakistan) American astrophysicist, Subrahmanyan Chandrasekhar (1910-1995) and the Brazilian astrophysicist, Mario Schönberg (1914-1990), who were the first to point out this limit and derive it.