Stars with less mass than 0.4 solar masses will evolve into white dwarfs. Stars between 0.4 and 3 solar masses will become red giants and then burn out into white dwarfs. Stars as massive as 6 solar masses may lose enough mass to eject planetary nebulae, and then die as white dwarfs. When atoms grow up, they want to be iron. Iron atoms are the most tightly bound of all atomic nuclei.
Large stars can fuse atoms as large as iron, but can go no further.
When an iron core of a massive star collapses, a .supernova is formed, which ejects massive amounts of energy into the surrounding space. Stars that are more massive than 8 stellar masses eventually collapse explosively to produce supernovae. Unless the star is larger than about 25 stellar masses, what will be left is a neutron star. A neutron star is made by the gravitational fusion of all the electrons and protons of the constituent nova. When neutron stars emit radiation at regular intervals, they are known as pulsars.