There are many nuclear reactions taking place. Actually nuclear fission where the lighter hydrogen combine to form the heavier and inert helium. When the the hydrogen in the core runs out it will lose outward pressure. The star will thus contract which will increase the density of particules and that in turn will increase pressure to a point at which the star will go supernova. If th star is big enough then it may create a black hole when it explodes.
What happens to a stars nuclear energy generation change if the core decreases in temperature?
nuclear fusion
Fusion and Fission happens at the stars' core.
Yes, if the star is massive enough when the core collapses a supernova explosion happens.
A stars core temperature will be several million kelvins
Nuclear Fusion occurs in the core of stars.
Nuclear Fusion at the Stars' Core.
Supernovae occur in stars that have reached the end of their life cycle and have run out of nuclear fuel to support their core. This typically happens to massive stars with at least eight times the mass of the sun.
When a star's core collapses and a giant explosion occurs, it is called a supernova. This explosive event releases an immense amount of energy and can outshine entire galaxies for a brief period of time.
A white main sequence star has the hottest core.
These are stars that have exhausted their core's supply of hydrogen by switching to a thermonuclear fusion made of hydrogen in a shell that surrounds the core.
They are called Core Burning Stars the smallest one is OGLE-TR-122b.