Thread by @starstrickenSF

decided to go out on a limb and make #SupernovaeSaturday a thing so I have an excuse to talk about supernovae all day 🙈. BUCKLE UP, GUYS.

so, we know supernovae are big and bright exploding stars. but what MAKES a star explode? do all stars explode? do all supernovae come from the same types of stars? what happens after they explode? well, lemme tELL ya: it’s..complicated.

some supernovae (SN) come from massive stars. HUGE. like, between 8x the mass of our Sun and >100x the mass of our Sun!!! can you imagine something that big?? (spoiler: I study them and I can’t. not really.)

these big SN are called core-collapse supernovae (CCSN). stars live by a process called fusion, essentially making heavier and heavier elements in their cores. that fusion requires energy and emits light as a byproduct. we *see* that light as stars shining!!

in fact, by classical physics, stars would have to get WAY too hot to fuse normal elements! so...how do stars *actually* fuse? well, the answer’s in the details...~QUANTUM MECHANICS~

scary (and cool!) physics term, but what does quantum mechanics actually do in this scenario? let me walk you through it.

there’s an energy barrier that atoms have to surmount in order to fuse. that’s where the high temperatures come in.

classically, atoms need high temperature to overcome the barrier. but in quantum mechanics, particles are treated as waves and can “tunnel through” the barrier! that means that some non-zero fraction of particles can end up fusing, when classically they shouldn’t be able to!!

so, stars shine because of QUANTUM MECHANICS. how cool is that???

let’s get back to supernovae. the CCSN types (remember, big stars) are able to fuse up to the heavy element iron. but once they reach iron, they hit the barrier. even quantum mechanics can’t get them through.

at this point, the star has lost it’s main source of pressure from fusion! to compensate, the star shrinks...UNTIL another pressure kicks in. this is another quantum mechanical pressure called “neutron degeneracy”. cool name, huh 🤗

this pressure results in an energy that releases a ton of ~neutrinos~. what are those, you may ask? neutrinos are suuuuper low-mass particles that get emitted weak nuclear reactions. they’re so light that they stream through ordinary matter, no problem!

neutrinos start to stream out of the star at an energy larger than the binding energy of the code— the energy keeping the core intact.

at this point, the neutrinos power the explosion!

the pressure in the core reduces so much that material around the core starts to fall in....collapsing the star! (hence the “core-collapse” in “core-collapse supernovae” 🤗)

OK! you made it this far. now, what about the smaller stars?

other SN come from really low mass stars called, white dwarfs (WD), in binaries. that means 2 stars are orbiting each other and transferring mass from one to the other. sometimes, it’s a WD + a normal bigger star. other times, it’s a WD + another WD.

now, these things are a little weirder. we’re not sure exactly what *causes* these explosions!

one model, called “detonation”, drives a veeery fast shock into the surrounding medium. but this produces too much iron and too little intermediate mass elements. not the perfect answer.

another model, called “deflagration”, has slower velocities. these models have hot material running into colder stuff, heating it up and igniting it. think of fire! problem is, this makes too little iron and too much intermediate mass elements! we need a middle ground!

astrophysicists posit the “delayed-detonation” model as the solution. here, the expanding shockwave starts slow, making lots of iron. the energy causes the star to expand and ignite the detonation!

some models have crazy cool (and complicated): s/o to @kenjshen on his 6-D model (dynamically driven double degenerate double detonation) model 🤯🤗. but we can dissect what this means now! a dynamically driven model that’s double degerante (2 WDs) with 2 detonations. COOL!

pretty pictures of a supernova explosion cuz y’all just read a whole lot of physics and these things are just so god damn pretty.

(for reference, this is the Crab Nebula, the remnants of a supernova that exploded in 1054)