As their name suggests, supergiants are very big! Let’s take a look at a famous example of a supergiant – Betelgeuse. Betelgeuse has a radius 1000 times the size of our Sun. It expels more energy as well – 135,000 times the energy of our Sun.
Another famous supergiant is the North Star, Polaris. Polaris is actually a multiple star comprised of three different stars. The main star, Polaris A, is fifty times the size of our Sun. It is 2,500 times as bright as our Sun!
How do Supergiants form?
Giant stars are an important part of a star’s life cycle. When a star is young, it releases energy from nuclear reactions. These reactions convert hydrogen to helium. When most of the star’s center is helium, it will start to get smaller. As the outer layers convert to helium, the star greatly expands. It will also begin to make thousands of times more light than it had before.
The surface of this new star is bigger, so its energy is spread out over a larger area. This causes the star to be cooler. At a certain size, the star will cool and become red, orange, or blue. Lower mass stars become red giants. High mass stars will become red supergiants. Giants and Supergiants emit huge amounts of energy. This results in lifespans that are shorter than most other stars.
When supergiants die, they explode with large amounts of energy. These explosions are called supernovas. Supernovas will usually leave behind neutron stars. When a very large star supernovas, it will leave behind a black hole.
When a star expands, the most common giant that will form is called a red giant. As the red giant grows, it becomes a red supergiant. When our Sun expends the hydrogen in its core, it will also become a red supergiant. At that size, it will swallow Mercury, Venus, and Earth. Depending on how large the red giant is, the end of its life will be different.
Some supergiants explode in supernovae that create neutron stars. A neutron star is a very small, dense star. A teaspoon of a neutron star would weigh 6 billion tons! The largest supergiants explode in supernovae that create black holes. Black holes are the densest objects in the universe. Their gravitational pull is so strong, light cannot escape.
Blue supergiants are much rarer than red supergiants. They only form from particularly massive stars. Blue giants and supergiants are hotter and brighter than red supergiants. They are smaller than red supergiants, but are more massive. Remember – large and small refer to size, but massive refers to its mass! The star Rigel is an example of a blue supergiant. Just like red supergiants, blue supergiants will eventually explode in spectacular supernovae.
Other Great Resources
ThoughtCo – Blue Supergiant Stars – https://www.thoughtco.com/blue-supergiant-stars-3073592
Supergiant Stars – Universe Today – https://www.universetoday.com/25325/supergiant-star/
Blue Supergiant Explosion – NASA Goddard –