If Betelgeuse Went Supernova

Factual Questions
21

Would they be ionized at that point, though? That’s a long time for recombination…

To be clear, it wrote a Python script to compute the results, which I inspected and ran locally; it didn’t just spitball.

The basic computation looks ok. However, the greatest weakness seems to be with regards to the energy spectrum, where it made some assumptions that are probably not justified. It assumed an average energy of 10 GeV for the supernova neutrinos (giving a range of resulting particle flux based on a 1% to 10% conversion efficiency), but then took a background flux that seemed to come from a higher energy scale. I suppose that in reality you’d have to bin things across the energy spectrum as opposed to taking a point sample. Especially when considering health effects.

I’d probably have come up with a similar answer had I SWAGged it myself, but in either case it should be taken with a grain of salt.

Note that I was just giving an upper bound to the mass increase :slight_smile: (and also, a rough sense of scale to the quantities we’re talking about). Still, very interesting info. Didn’t realize that there could be a mass decrease.

22

Recombination is a three-body process so it’s actually rather slow in the interstellar medium. One mean-free-path of distance will be traversed much faster than the recombination time.

(It looks like you quoted a piece of text that was ignoring the dominant processes and letting the ions be magically transported all the way to earth. I figured that wasn’t the scenario you were actually referring to here, since that breaks so much physics to even start, but maybe I misinterpreted.)

That’s precisely my point. I expect it could do a great job of helping construct reasonable tools to take inputs and do calculations, but I think it will have no idea about what physical phenomena to consider and what quantitative inputs to suggest when it does stumble down a plausible alleyway.

That’s wild. “GeV” and “supernova neutrino” have no business being in the same breath. You should scold the AI and see what it has to say for itself.

Not sure what you mean by “conversion efficiency” or “background flux”. Maybe “background flux” means “non-supernova-related flux”? For the mass question this doesn’t seem relevant, and for the human safety question, neutrinos don’t seem relevant.

What’s fun with the “added mass from neutrinos” question is that the first, second, and third steps one might reasonably take to set the scale for a SWAG are all wrong (which is why I don’t expect AI to have any hope.)

First thought: neutrino interactions definitely contribute mass to the earth. This is a false start since the neutrino can just leave after interacting, and whether they do that essentially always, essentially never, or a very narrow sweet spot in between depends on the energy regime in question.

Second thought: okay, some classes of interactions contribute mass, and the scale of the mass increase is the number of such interactions times the mass of the neutrino. This is also a false start; the neutrino mass is irrelevant and could even be set safely to zero for simplicity.

Third thought: okay, the scale of the mass increase is the number of such interactions times the typical neutrino energy. This is a false start because it’s not the neutrino’s properties that matter but rather the reaction’s earth-bound initial and final constituents’ properties, and changes in these are limited to energies around the scale of nuclear transitions regardless of the incoming neutrino energies. Any additional massive objects realized from higher neutrino energies will be ephemeral.

So, it turns out that a SWAG is only SWAGging in this case if it’s based on “typical nuclear transition energies” times “number of neutrino interactions”, and, for added flair, also times “fraction of those interactions that can muck about with the nucleus in the first place”, which can be grossly taken as \mathord{\ll}1\% or 100\% depending on the neutrino energy regime.

23

There are two different things we’re talking about. First is that a supernova blows off a bunch of stuff at relatively low speeds (<10% c). It’s a lot of matter, and you can calculate how much would hit Earth if it actually got here. The book (by Phil Plait) calculated about 100 tons from the star that exploded into the Crab nebula. That would be about 10,000 tons from Betelgeuse, within the usual order-of-magnitude bounds. Plait adds that it wouldn’t actually get here.

The second thing is about cosmic rays produced by the supernova, and the question of whether it would harm a mission to Mars. They experience a cosmic ray flux from various sources already, and over the course of several months it’s a non-trivial health concern. Some of those sources are supernovae. But would the flux from Betelgeuse exploding be a significant increase over the background? I suggest yes.

Sorry, that was my error. I’d just read your bit about neutrinos and had that in my head. The calculation was about protons. I.e., most of what constitutes “cosmic rays”.

Again, the original question was about a trip to Mars. The comparison is between usual cosmic ray background levels vs. the dose you would get from Betelgeuse.

Conversion efficiency is basically how much of the supernova’s energy gets converted to cosmic rays. It gave a range of 1-10%. That doesn’t seem out of bounds with the papers I can find:

The energy released in supernova explosions satisfies the energy requirement to maintain cosmic ray energy density in the galaxy considering an overall ∼ 10% efficiency of the conversion of explosion energy into cosmic ray particles.

But even with an efficiency figure you need to assume an energy spectrum to compare.

24

Wikipedia has a list of largest nebulae:

The largest listed “supernova remnant” is Simeis 147, which has a diameter of ~160 ly. So matter can be distributed up to 80 ly.

There are some larger nebulae that are driven by supernova action but aren’t strictly a result of them (H II regions).

So Betelgeuse is probably still too far away at 640 ly for the matter to get to us. Still, 80 ly isn’t too shabby.

25

Ah, that makes sense!

Thanks. Yeah, that part of the discussion came in after I wrote most of my post related to other points, so we both had some distracting mental anchors in play.

That sounds reasonable. So whether those protons can bee-line it to earth is the question. And as above: the energies are way too low. The cyclotron radius (i.e., radius of path curvature) in the interstellar magnetic field is tiny compared to the hundreds of light years betwixt us and Betelgeuse. You have to get to crazy energies beyond 1018 eV before some sense of directionality is maintained, and, as your most recent link quite coincidentally discusses, supernovae don’t contribute cosmic rays anywhere close to such energies.

(As an aside: This cosmic ray spectrum on a log-log scale shows how the flux drops like a rock with energy, so the vast majority of cosmic rays have the tiniest of cyclotron radii. At ~1 GeV, the radius is just a few million kilometers. This is why cosmic rays on the left half of this spectrum are very isotropic.)

26

Great article!

But I bet you might be able to see the nova in the daytime. if you knew where to look, I bet it would be the brightest object in the night sky.

27

So what are the odds that Betelgeuse (warning: don’t mention the name in this post again!) has already gone supernova and we’re just waiting on the opening scene?

p.s. I like potatoes

28

Might be as high as ~1%. If it happened within the last 640 years, the light would still be on its way. The usual estimates I see say that it should happen within around 100,000 years. So… divide and you get 0.6%. There’s a lot of uncertainty, though.

29

One issue with supernova cosmic rays on a Mars mission or the like is that they’d be unexpected. Most of the radiation you’d expect to get on such a mission would be from the Sun, and so to deal with that, you might do something like putting a big tank of water or fuel between the Sun and the astronauts, for fuel. But that tank won’t be positioned right to shield from a supernova.

30

But a cylindrical/annular tank would.
Wait out the event within the inner cylinder as a fallout shelter.

31

But for that, you’d need a sufficient thickness of shielding in all directions around you, not just in one direction, which would require a lot more shielding.