What Is a Supergiant Star?

Massive Stars

• Massive stars are defined as those that have a mass at least three times that of the Sun. Some of them have as much as 50 times the mass of the Sun. The more massive a star, the quicker it exhausts its hydrogen supply and therefore the shorter its life is. The process of turning hydrogen into helium takes billions of years in an "ordinary" star, but only millions of years in a massive star -- a relatively short time in space. Because of how short the lifespan of these stars is, there is simply no time for planets to form around them.

Red

• A red supergiant is one phase in the life cycle of a massive star, when the star is on the decline. When the supply of hydrogen in the core of the star runs out, the core shrinks and the temperature increases. Over the next million years or so, the star continues to burn, turning the carbon core into oxygen, then neon, silicon, sulfur and finally iron. While this nuclear fusion is taking place, the volume of the star increases as the gases cool and expand, and this is when it becomes a red supergiant. The star burns brighter than it did in its earlier phases, but shines with a red glow, hence the name.

Blue

• The most massive star ever found in the galaxy is a blue supergiant, known as R136a1, and it lies 165,000 light years from earth. R136a1 has 265 times the mass of the Sun. Blue supergiants are hotter and give off more energy than red supergiants; the brighter the color of the star, the hotter it is, so red stars are actually some of the coolest. Both red and blue supergiants go through the same nuclear processes in the core, hence they can start off as red supergiants and become blue, or vice versa -- it all depends on the mass and temperature of the star.

Betelgeuse

• The star Betelgeuse is one of the best examples of a red supergiant star and can be seen in the shoulder of the constellation Orion. It is also one point of the Winter Triangle which can be seen from North America. Betelgeuse sits around 310 light years from Earth and has 10,000 times the brightness of the Sun. The radius of this star has been worked out to be around 370 times that of the Sun, and in fact if it were positioned in the middle of our solar system where the Sun is now, Betelgeuse would actually extend out past Mars.