Stellar Evolution

Page 13

Summary

As we saw, the mass of the star is the most important factor that determines its evolution.
The diagram below illustrates stellar evolution of stars of increasing mass from bottom to top.

Source: http://chandra.harvard.edu/edu/formal/stellar_ev/

We have discussed three different outcomes in the final stage of stellar evolution.
The table gives a summary of these outcomes.

Original Mass	Mass of Core at end of Red Giant stage	Type	Stable due to
< 8 M_sun	< 1.4 M_sun	White Dwarf	Electron degeneracy pressure
< 8 M_sun	1.4 – 3 M_sun	Neutron Star	Neutron degeneracy pressure
> 8 M_sun	> 3 M_sun	Black Hole	No known force can withstand the gravitational pressure

Explanations

The limit of 1.4 M_sun is called the Chandrasekhar limit
Electron degeneracy pressure is the resistance of electrons in atoms
against the collapse of the atomic structure
Neutron degeneracy pressure is the resistance of the atomic nucleus
after electrons have been crushed into it, forming neutrons and neutrino's

Typical values for mass and size:

	size	mass
White Dwarf	Size of Earth	< 1.4 x M_sun
Neutron star	30 km	1.4 - 2.1 x M_sun
Stellar Black Hole	30 km (event horizon)	up to 100 x M_sun

Super massive black holes can have a mass of many million, even billion times M_sun. The largest detected super massive black hole to date has an estimated mass of 18 billion (1.8x10¹⁰) M_sun. Ref...