Compact objects

Question 1

How are compact objects different from the others ?

Answer 1

Normal stars use thermal pressure from thermonuclear reaction to compensate gravity. But when the fuel is exhausted, the thermonuclear reaction cannot keep going much longer. Other type of pressure arise. They come from Heisenberg uncertainty principle and Paul exclusion principle. For NS it comes from neutrons degeneracy. For WD it comes from electrons degeneracy. For BH there is no support pressure at all.

Question 2

Compactness parameter?

Answer 2

given by Rs / R*

Question 3

WD first observation

Answer 3

By William Herschel in 1783.

Question 4

What is the limit for the mass of a WD ?

Answer 4

Chandrasekhar limit

Question 5

How do we keep the neutrons alive in a neutron star?

Answer 5

The presence of relativistic electrons prevents the neutrons from going through a beta decay and turning into protons.