Red Giants

A red giant is a very old star. As a star gets older, it runs low on fuel. Then it grows bigger and cooler. Because it is cooler, it glows red or orange. Red giants are much larger than normal stars.

How They Form

Stars like our Sun burn a gas called hydrogen in their centers. When the hydrogen runs out, the star starts to puff up. The outside gets cooler and turns red. At the same time, the inside keeps burning other gases.

A diagram comparing a Sun-like star with a much bigger, puffy red giant.
A diagram comparing a Sun-like star with a much bigger, puffy red giant. (ESO / Wikimedia Commons)

The End of a Red Giant

A red giant does not last forever. After a while, it blows off its outer gas. What is left behind is a small, hot core called a white dwarf. The gas it blew off can form a pretty cloud in space.

Fun Facts

  • Some red giants are hundreds of times bigger than the Sun.
  • Betelgeuse in the Orion constellation is a famous red giant.
  • Red giants are cooler than our Sun, even though they look bright.

Did You Know?

In about 5 billion years, our Sun will become a red giant and swallow some of the inner planets!