Red giants are massive stars nearing the end of their lives. They are usually 5-10 billion years old, depending on the size of the star. Supergiants are much larger and much younger, usually 50 million years old or younger, very young for a star. These giants occur because a star is running out of unfused protons and the nucleus becomes composed of alpha particles (helium nuclei). The outer hydrogen is not hot enough to fuse. The star cools and outer layers fall into the core. A inner shell becomes hot enough to fuse hydrogen, but this radiation is weaker, so, as the heat in the core expands the star and this weaker radiation is the main source of light, the star becomes a red giant. If the star is a giant, it will soon cast away it's layers to become a planetary nebula, hiding it's now extremely dense core, an Earth-size white dwarf. The star, if it's a supergiant, eventually heats up enough to fuse alpha particles into larger ones, like carbon, nitrogen, and oxygen. If the alphas are used up, neon magnesium, silicon, and sulfur are made, which soon becomes iron. However, iron fusion uses more energy than it's worth, and with no force, gravity destroys the star. The star sheds it's layers in a monumental explosion, a Type II Supernova. The force fuses iron, making all of the elements heavier than iron. If the core has 1.5 to 3 times the mass of the Sun, an extremely dense city-size neutron star, which is made of neutrons. If it is greater, it makes a black hole, which makes a puncture in space-time continuum.