Main Sequence stars
A star goes through many changes in its life, from when it is born in a nebula, to when it dies and explodes. When the star has been born, and rapid and violent fusion has occurred, the star eventually becomes stable. A star spends most of its life in the stable position. A star experiencing this part of its life is called a ‘Main Sequence Star’ as it is living the main part of its life. During this stage, the star would only experience slight change in its luminosity and temperature. The amount of time a star spends in this phase depends on its mass. A very massive star will spend less time in this stage because it uses its fuel up quicker than a smaller star.
Red Giants
Near the end of its life, a star in the main sequence begins to run out of fuel. The outer surface expands and cools and the star becomes a Red Giant. These are extremely large (sometimes 100 times bigger than the original star). They are reddish orange, hence the name Red Giant. Very big stars expand to be a Red Supergiant.
White Dwarf
When a star is a Red Giant, the pressure and gravity have a struggle, and eventually don’t equal and the star collapses. The cool outer surface blows away from the core, forming a planetary nebula. What remains after this explosion is the dead core of the star. No more fusion occurs. The white dwarf is extremely dense, and even hotter. It glows a little by its remaining heat, and eventually loses all its fuel and heat and becomes a dead remain of its previous life.
