How do stars die?
Stars begin their lives when hydrogen fusion ignites in their dense, hot cores. Once that process starts, it’s game on. The gravitational pull of all the mass of the star tries to squeeze it down into a tiny point, but the energy released by fusion pushes outward, creating a delicate balance that can persist for millions or even trillions of years.
Small stars live an incredibly long time. Because of their small stature, they don’t need a lot of energy to balance the inward gravitational pull, so they only sip at their hydrogen reserves. In a bonus boost, the atmospheres of these stars constantly circulate, pulling fresh hydrogen down from the outer layers into the core, where it can fuel the continuing fire.
All told, a typical red dwarf star will happily burn hydrogen in its core for trillions of years. Not too shabby.
As these small stars age, they steadily become brighter until they just sort of vaguely sputter out, becoming an inert, boring lump of helium and hydrogen just hanging around the universe minding nobody’s business but their own.
It’s a sorrowful fate, but at least it’s a quiet one.
The grand finale
When the massive stars in our universe die, it’s much more violent. Because of the increased bulk of these stars, fusion reactions need to happen much faster in order to sustain the balance with gravity.
Despite being so much heavier than their red dwarf cousins, these stars have much shorter life spans: Within only a few million years (which given astronomical time scales might as well be next week) they die.
But when massive stars die, they go out in all their glory.Their huge size, means there’s enough gravitational pressure to not only fuse hydrogen, but also helium. And carbon. And oxygen. And magnesium. And silicon. A good number of the elements on the periodic table are produced inside these giant stars near the end of their lives.
All that material surrounding the iron squeezes in on the core, but iron fusion doesn’t release energy to counteract it. Instead, the core contracts to such incredible densities that electrons get shoved inside of protons, turning the entire core into a giant ball of neutrons.
That neutron ball is able to — temporarily, at least — resist the crushing collapse, triggering a supernova blast. A supernova will release more energy in a week than our sun will release over the course of its entire 10-billion-year lifetime. The shock wave and material ejected during the explosion carves bubbles in the interstellar medium, disrupts nebulas, and even sends material spewing out of galaxies themselves..
It’s one of the most spectacular sights in the entire universe. When supernovas happen in our neck of the galactic woods, the explosions are bright enough to appear during the day and can even be brighter than the full moon at night.
Pretty intense, and what a way to go.