In stellar

astrophysics Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the he ...

, the Schönberg–Chandrasekhar limit is the maximum mass of a non-fusing,

isothermal In thermodynamics, an isothermal process is a type of thermodynamic process in which the temperature ''T'' of a system remains constant: Δ''T'' = 0. This typically occurs when a system is in contact with an outside thermal reservoir, an ...

core that can support an enclosing envelope. It 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 (10% to 15% of the total stellar mass).The Schoenberg-Chandrasekhar limit: A polytropic approximation, Martin Beech, ''Astrophysics and Space Science'' 147, #2 (August 1988), pp. 219-227. DO
10.1007/BF00645666
This is the maximum to which a helium-filled core can grow, and 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 the astrophysicists

Subrahmanyan Chandrasekhar Subrahmanyan Chandrasekhar (; ) (19 October 1910 – 21 August 1995) was an Indian-American theoretical physicist who spent his professional life in the United States. He shared the 1983 Nobel Prize for Physics with William A. Fowler for " ...

and Mario Schönberg, who estimated its value in a 1942 paper.On the Evolution of the Main-Sequence Stars
M. Schönberg and S. Chandrasekhar, ''Astrophysical Journal'' 96, #2 (September 1942), pp. 161–172. They estimated it to be

\operatorname_ = 0.37 \left(\frac\right)^2

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, the star leaves the main sequence with a core mass already greater than the Schönberg–Chandrasekhar limit so its core is never isothermal before 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.the evolution of high-mass stars
, lecture notes, Vik Dhillon, Physics 213, University of Sheffield. Accessed on line April 27, 2007.

References

{{DEFAULTSORT:Schonberg-Chandrasekhar Limit Astrophysics Stellar astronomy Stellar dynamics