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Schönberg-Chandrasekhar Limit

(maximum stellar isothermal helium core mass)

The Schönberg-Chandrasekhar Limit is the maximum stable isothermal mass of the Helium Stellar Core formed from Fusion in a Main Sequence Star. A core is isothermal (same Temperature throughout) if the energy source (fusion) surrounds it (i.e., forming a shell) and everything is sufficiently stable that the core falls into and essentially remains at equilibrium. Only stars in a certain mass range grow such a core large enough to reach the limit. For those that do, helium fusion begins and the star enters the Red-Giant stage.

The limit depends upon factors in the star:

Mcore/M ≈ 0.37(μenvcore
  • Mcore/M - the limit (≈ 8%).
  • Mcore - mass of the core.
  • M - mass of the whole star.
  • μcore - mean molecular mass of the core.
  • μenv - mean molecular mass of the envelope, the rest of the star.