Why do some stars burst to create fulgurant flashes of light and cause the emission of huge quantities of enery? That depends on the star’s mass: a massive star will live for a rather short period of time, such as several millions of years, which really are a trice in the life of a star. This is because a star converts its hydrogen into helium much quicker when it is more massive, the particles in the core of the star being more excited, and thus combine at a much more rapid rate, by the extreme pressure and heat inside it.

Most of the less massive stars die when they’ve reached a stage where they can’t combine the atoms that make it. The truth is that even if the core of the star, which as originally hydrogen, is now helium, there is still a tiny bit of hydrogen in the absolute center of the star, and then helium around it. The helium atoms are then forced to combine in even more complicated atoms, such as carbon and oxygen, if the star’s mass allows it. If it does, we now have a layered star, like an onion, with hydrogen in the middle, helium around it, and more complicated atoms on the edges. This causes instability inside the star. It expands so much that it becomes a Red Supergiant, much like our Sun will be (when the sun will, it’ll reach up to Mars - meaning that Earth will be engulfed by the sun). Current Red Supergiants include Antares for example, which is very noticeable because of its red color (Antares means in Greek Mars’ rival, because of its color), visible in Summer at our northern latitudes. Most stars end there lives like this, choking at itself, and forming a beautiful planetary nebula, like the Dumbbell Nebula (Messier 27).

But if the star is massive enough, it’ll continue converting the heavy elements into even more heavy elements, making the star even more unstable. It all ends when the core is made of iron: All of the matter of the star is sucked towards it, and hits the iron surroundings of the core. The matter is then projected with extremely violent energy and speed into the space around it. It emits more enrgy in a second than the energy it has made during its whole life. Supernova thus contribute to enseminate space with new, heavier elements. They are thus in part responsable for life on Earth, and make very interesting objects for astronomers to observe.
Clement