In this series we are exploring the weird and wonderful world of astronomy jargon! You’ll have a blast learning about today’s topic: Type-II Supernovae!
When stars like our sun die, they turn themselves inside out in a gory, grisly display of fundamental elements. Despite the carnage it winds up being a pretty sight, creating the beautiful planetary nebulae.
But for stars bigger than the sun, they go out with a bang.
The problem is fusion. That’s how stars get their energy. Right now our sun is burning through several mountains’ worth of hydrogen every single second, leaving behind helium. As it ages, it will turn to burning that helium, producing carbon and oxygen. Not giving up quite yet, it will fuse that carbon and oxygen into silicon, magnesium, and iron.
And it turns out that iron is the end of the fusion line.
Once iron appears in the core of a giant star, you’re only minutes away from a Type-II (also known as “core collapse”, but that’s giving away the ending) supernova.
With each successive generation of heavier elements, the fusion rates happen faster and faster. That’s because the heavier elements yield less energy than their lighter cousins, and so the crushing gravity of the star’s own weight cranks up the intensity.
But fusing iron doesn’t release energy. It takes energy.
As soon as the iron core develops, the rug has been pulled out from underneath the star. All the surrounding material crushes into that tiny core at a healthy fraction of the speed of light. That material slams into the core with such a force that electrons get shoved inside protons, turning the whole core of iron into a giant ball of neutrons.
That ball of neutrons (properly called a “proto-neutron star”) can, temporarily at least, resist the continued collapse. So all that material bounces off the core, triggering a shockwave.
And a big, big boom.
A Type-II supernova.
Supernova types are spectral types. Type II SNe spectra are characterized by the presence of strong Hydrogen emission lines. That’s it.
What you’ve described here is the theoretical model (strongly supported by SN 1987a) for the progenitor of several types of SNe II being a massive (> 8 solar masses) star that has evolved to the point of producing an iron core. It is also worth noting that such massive stars can produce type I supernovae if they have shed most of their hydrogen outer atmosphere prior to core collapse.
I know it has become popular to conflate the spectral types with their progenitors, but there is a difference and professionals should be careful to distinguish among matters.