Schönberg-Chandrasekhar limit

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In stellar astrophysics, the Schönberg-Chandrasekhar limit gives the maximum mass of a non-fusing, isothermal core which can support an enclosing envelope. The limit is expressed as the ratio of the core mass to the total mass of the core and envelope. Estimates of the limit depend on the models used and the assumed chemical compositions of the core and envelope; typical values given are from 0.10 to 0.15.^[1][2] The limit is named after the astrophysicists Subrahmanyan Chandrasekhar and Mario Schönberg, who estimated its value in a 1942 paper.^[3]

The Schönberg-Chandrasekhar limit comes into play when fusion in a main-sequence star exhausts the hydrogen at the center of the star. The star then contracts until hydrogen fuses in a shell surrounding a helium-rich core, both of which are surrounded by an envelope consisting primarily of hydrogen. The core increases in mass as the shell burns its way outwards through the star. If the star's mass is less than approximately 1.5 solar masses, the core will become degenerate before the Schönberg-Chandrasekhar limit is reached, and, on the other hand, if the mass is greater than approximately 6 solar masses, gravitational collapse will release so much energy that the core will not become isothermal prior to the start of helium fusion. In the remaining case, where the mass is between 1.5 and 6 solar masses, the core will grow until the limit is reached, at which point it will contract rapidly until helium starts to fuse in the core.^[1][4]

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