He burning - 1 million years. Si burning - 1 week. Even though the core temperature is 6 billion degrees. The core of the star is squeezed incredibly tightly by gravity. Electrons in atoms combine with protons.
Neutrinos fly out of star.
Core of a star converted into a huge ball of neutrons - neutron star. Neutron Star - the very end of certain massive stars. Star gets very bright during collapse - can outshine entire galaxy. The outer layers of the star do not go into the neutron star but are ejected with extremely high velocity - make a supernova remnant. Far more violent than a planetary nebula.