The Birth and Death of a Star

Our Sun is a main sequence star. It started its life as a nebula (or protostar). Once they accumulate enough energy, fusion ignition occurs. This sends the star to its next stage in life, the main sequence.

Main Sequence Stars - The main sequence is the point in a star's evolution during which it maintains a stable nuclear reaction. It is this stage during which a star will spend most of its life. Our Sun is a main sequence star. A main sequence star will experience only small fluctuations in luminosity and temperature. The amount of time a star spends in this phase depends on its mass. Large, massive stars will have a short main sequence stage while less massive stars will remain in main sequence much longer. Very massive stars will exhaust their fuel in only a few hundred million years. Smaller stars, like the Sun, will burn for several billion years during their main sequence stage. Very massive stars will become blue giants during their main sequence.

Red Giants - A red giant is a large star that is reddish or orange in color. It represents the late phase of development in a star's life, when its supply hydrogen has been exhausted and helium is being fused. This causes the star to collapse, raising the temperature in the core. The outer surface of the star expands and cools, giving it a reddish color. Red giants are very large, reaching sizes of over 100 times the star's original size. Very large stars will form what are called red supergiants. Betelgeuse (below) in Orion is an example of a red supergiant star.

White Dwarfs - A white dwarf is the remnant of an average-sized star that has passed through the red giant stage of its life. After the star has used up its remaining fuel, the star may expel some of its matter into space, creating a planetary nebula. What remains is the dead core of the star. The core glows because of its residual heat. Eventually the core will radiate all of its heat into space and cool down to become what is known as a black dwarf. White dwarf stars are very dense. Their size is about the same as that of the Earth, but the contain as much mass as the Sun. They are extremely hot, reaching temperatures of over 100,000 degrees.

Black Holes-A black hole is what is left over after a red supergiant (Above average size red giant) implodes (Supernova) and leaves a black hole. It is region of space in which the gravitational field is so powerful that nothing can escape after having fallen in. It gets its name for obvious reasons, it is so strong that not even light can escape it. There are many controversies over black holes and where they lead. I believe that it will be argued about for many years.