Re: Why do supernovae occur?

Great Question!

As you learned in third grade, Supernovae are the enormous explosions of dying stars. Stars, like our Sun are made up of gases like hydrogen and helium. The gravity of stars is very strong - so strong our Sun's gravity keeps us in orbit around it. The gravity of stars pulls all the gases closer and closer together and this pressure creates a lot of heat. This heat causes the hydrogen in stars to burn and that's what makes stars shine.

However, every star only has a limited amount of hydrogen to burn. Just like every car has a certain size gas tank, all stars have different amounts of gas and run out eventually. Smaller stars like our sun will then become red giants, and eventually small earth-size objects called white dwarfs. Big stars have stronger gravity and so they get crushed by gravity even more than our sun will when it dies. The powerful forces of gravity it these huge stars heat them up so hot that they explode in the enormous explosion we call a supernovae. In a supernovae the outer layers of the star are blown millions upon millions of miles away from the core of the star. Supernovae explosions can span light years across. During a supernovae gravity continues to affect the core of the dying star. If the remaining core is big enough to cause the gravity to be strong enough, the star will then become a black hole.

I find the death of stars to be one of the most interesting parts of Astronomy. I'm glad it interests you as well.

Todd Boring

Note from the moderator

For completeness sake, I would just like to point out that supernovae come in two flavors. The first and most common is the one dicussed by Todd above and is known by astronomers as "core-collapse supernovae". The second type of supernovae consist of huge explosions too but astronomers are not sure what causes them. The most popular theory is that it is the result of the sudden detonation of a white dwarf (Todd explained above what a white dwarf is) which is accreting material from a companion star.

The colors (spectra) of these two types of supernovae are different and that is how we know that they must be different.

Marc Herant, astro moderator.