Supernova

They also enrich the galaxy with heavy elements, spreading the products of stellar fusion outward into the interstellar medium.

Cosmic rays accelerated from supernova remnants fill the galaxy.

Supernovae do not just create shells of gas.

They accelerate particles to nearly the speed of light, creating cosmic rays that permeate the galaxy.

Some of these cosmic rays reach Earth, creating a constant low-level radiation exposure.

That's a number sufficiently low that we could be confident that even life on Earth here should be able to recover and thrive again.

So when it comes to supernovae, basically the entire galaxy is currently habitable.

Supernovae are not totally irrelevant though, because the current state of our Milky Way galaxy is not the way that it always was.

In the past, there was more gas enabling higher rates of star formation.

More star formation means more massive stars, which in turn means more supernovae.

To get the atoms out of the center of the stars, you have to blow up the star and distribute the stuff throughout the universe.

The cosmos is seeded, therefore, through these supernova explosions with the atoms of life.

Supernovae have to occur in exactly the right way or they will annihilate life rather than nourish it.

Conditions must be exactly right for the explosion of supernovae.

Too many supernovae and there's no life in the universe.

But other theorists have thought about this kind of thing, like Mitch Begelman, a theorist currently at the University of California 20 years ago, he and his collaborators developed a theory for what they call a quasi-star, which would be one specific recipe for how to make a black hole star.

They were thinking, like, are there any more creative ways to make a very big, massive black hole with a, that's very bright? And they were saying, "Well, you know, well, what is a black hole? It's a collapsed star, right? Supernova." At least I generally think that the supernova pushes off a whole bunch of gas and pushes that far away, and we forget about that, and the center collapses and makes, like, a relatively clean black hole.

Right.

I'm sure there's what we can tell us.

Mm-hmm.

Supernovae act like massive aerosol cans, spraying the universe with metallic dust and gas.

So our pristine shielded gas cloud is sitting in a neighborhood that is getting increasingly toxic.

Very toxic.

A massive star runs out of fuel, gravity crushes it inward, boom.

Supernova.

Exactly.

But the sheer extremity of the specific star's current state is really where we need to start.

Yeah.

Supernovae go off and blow gas out of the galaxy.

Black holes blast radiation that halts star formation.

These localized events alter the appearance and behavior of a specific galaxy, which makes it a slightly unreliable tracer of the underlying pure physics of the universe.

Exactly the issue.

Supernovae destroy complex chemistry.

So these low velocity cloud collisions provide this perfect Goldilocks physical condition.

Not too hot, not too cold.