After a red giant explodes, the core that is left over is called a white dwarf. It has no way of obtaining more energy and will cool off until it is dark, then turn into a black dwarf. Sometimes a white dwarf will move too close to a large star and pressure from the star will cause it to explode. From Earth, this explosion looks like a bright, new star. This object is called a nova, which means new .
Some stars are three times larger than the sun and are called massive stars.
Their life cycle is somewhat different from that of regular stars. As temperatures heat up and the star cools, nuclear fusion occurs and eventually the energy runs out. When this occurs, the core is crushed by the tremendous weight of the star and an explosion takes place. What results is called a supernova. Often, there is a tightly packed core left over from the explosion, which becomes a new kind of star.