Schoenberg-Chandrasekhar border
The Schönberg-Chandrasekhar limit is the upper limit for stars up to which an isothermal core can withstand the pressure of the surrounding shell. It is usually expressed as the ratio of the mass of the core to the total mass of the star. Calculations show that it is around 0.1 regardless of the star's mass. It is named after Mario Schönberg and Subrahmanyan Chandrasekhar , who first derived it.
When the hydrogen in the core of medium-sized stars is used up, energy production in the center comes to a standstill and an isothermal core of helium is formed. Since hydrogen burning continues to take place in a shell around the core , the mass of the core increases continuously. When the Schönberg-Chandrasekhar limit is reached, i.e. when the mass of the core makes up about 10% of the total mass, the core collapses and the shell expands to form a red giant . In the Hertzsprung-Russell diagram , the star develops from the main series into the area of the Hayashi line .
This process is quick compared to the time spent on the main row. It is therefore unlikely to observe him. (A star with 5 solar masses stays on the main sequence for about 80 million years; it takes about 3 million years to develop into a red giant.) This explains the Hertzsprung gap , the area in the Hertzsprung-Russell diagram where only a few stars are observed.
literature
- Rudolf Kippenhahn , Alfred Weigert , Achim Weiss: Stellar Structure and Evolution. 2nd Edition. Springer-Verlag Berlin, 2012. ISBN 978-3-642-30255-8 , section "30.5 The Schönberg-Chandrasekhar Limit", pp. 356-363.