Statistical Mechanics - Astronomy Short Qs

1.Why is nuclear burning in a star supported by electron degeneracy pressure unstable?

2.What quantity is equivalent to temperature when we talk about a self-gravitating group of objects?

3.How do we know the centre of our Galaxy contains a supermassive black hole?

4. Why is quantum mechanical tunnelling necessary for fusion reactions to occur in stars?

short but understandable answer! Thanks!