Why does a helium flash occur under some circumstances and not under other circumstances when helium fusion begins?

Question

What will be an ideal response?

Answer 1

When the temperature in the core of a star becomes hot enough, helium fusion begins to make energy and the temperature rises, but pressure does not increase because the gas is degenerate. The higher temperature increases the helium fusion even further, and the result is a runaway explosion called the helium flash. Stars less than about 0.4 solar mass never get hot enough to ignite helium. Stars more massive than 3 solar masses ignite helium before their contracting cores become degenerate.