Chandrasekhar limit

The Chandrasekhar limit is the theoretical upper limit for the mass of a white dwarf, which was derived from the Indian-American astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar. Regardless of Chandrasekhar same ceiling earlier by William Anderson (1929, Tartu ) and Edmund Stoner (1930, Leeds ) was calculated.

After the termination of his nuclear fusion processes falls a star like the Sun in on itself and forms a white dwarf. This is possible for all stars whose mass is below the Chandrasekhar limit. Otherwise, the pressure of the stellar matter is not sufficient to stabilize the white dwarf. Instead takes place depending on the mass collapse to a neutron star or black hole.

White dwarfs are described as an ideal degenerate electron gas. The derivation of the Chandrasekhar limit is therefore based on quantum statistical mechanics, more precisely on the Fermi -Dirac statistics, because they are fermions at Electron. Effects of general relativity can be ignored while left, as they play a role only when more compact stars. The formula for the limiting mass is given by

It is the solar mass, and indicates how many nucleons are in the middle of an electron, assuming that white dwarfs are electrically neutral. The stellar matter is composed of atoms with this nucleons and protons.

Examples

For white dwarfs which consist mainly of the isotope of carbon or oxygen isotope is

.

It follows directly mentioned the critical mass of 1.457 solar masses. An example of such a star is Sirius B, however, is for white dwarfs with an iron core of

.

Your mass limit is therefore at 1.256 solar masses. The Chandrasekhar limit is therefore not to be understood as meaning that it is the same for each star. So it rather depends on the type of stellar matter, which is present in each ceiling.

Thermonuclear supernovae Ia are interpreted as a consequence of exceeding the Chandrasekhar mass limit. These supernovae show a fairly uniform course of the light curve and in their absolute brightness. A subset of supernovae of type Ia super- Chandrasekhar - Ia supernovae, has a significantly higher luminosity, which suggests a mass of up to 2.5 solar masses in a collapsed white dwarf. It has been attempted to model white dwarfs with high magnetic field densities, thus the degenerate matter is stabilized against collapse. However, Lorentz forces should prevent a sharp increase in the Chandrasekharschen mass limit.

Neutron stars and quark stars

For neutron stars, there is an equivalent limit, the Tolman -Oppenheimer - Volkoff limit. Similarly, a corresponding limit is assumed for the hypothetical quark stars, but the equations of state of these exotic types of degenerate matter are not yet precisely known.