Podcaster: Fraser Cain & Dr. Pamela Gay
Title: Astronomy Cast: Ep.Ep. 750: Supernova Early Warning System
Organization: Astronomy Cast
Link: http://www.astronomycast.com
Description: Streamed live on Mar 31, 2025.
When enormous stars detonate as supernovae they release a burst of neutrinos that can be the first sign of a coming explosion. Now, astronomers have built a network to watch for that flash of neutrinos, and help direct their telescopes for when the sky show begins. Supernovae explosions occur in stages, with neutrinos being emitted hours before photons. If we can accurately detect those neutrinos, we might just be able to get on target before the light show even starts…. Maybe.
Bio: Fraser Cain is the publisher of Universe Today and Dr. Pamela Gay is a Senior Scientist at Planetary Science Institute and a Director of CosmoQuest. They team up to do Astronomy Cast, a weekly facts-based journey through the cosmos
Today’s sponsor: Big thanks to our Patreon supporters this month: Paul M. Sutter, Chris Nealen, Frank Frankovic, Frank Tippin, Jako Danar, Michael Freedman, Nik Whitehead, Rani Bush, Ron Diehl, Steven Emert, Brett Duane, Don Swartwout, Vladimir Bogdanov, Steven Kluth, Steve Nerlich, Phyllis Foster, Michael W, James K Wood, Katrina Ince, Cherry Wood.
Please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at signup@365daysofastronomy.org.
Please visit our Patreon page: https://www.patreon.com/365DaysOfAstronomy
or you can consider to sponsor a day of our podcast : https://cosmoquest.org/x/365daysofastronomy/product/sponsor-an-episode-of-365-days-of-astronomy/
Transcript:
[Fraser Cain]
AstronomyCast, Episode 750, The Supernova Early Warning System. Welcome to AstronomyCast, our weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the publisher of Universe Today.
With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?
[Dr. Pamela Gay]
I am doing well. Happy 750th episode, Fraser.
[Fraser Cain]
This is it, 750 episodes, and we’re going to celebrate by producing an episode of AstronomyCast.
[Dr. Pamela Gay]
Which is like science, science. We need science.
[Fraser Cain]
That’s just what we do. That’s why we’re here. So when enormous stars detonate a supernovae, they release a burst of neutrinos that can be the first sign of a coming explosion.
Now astronomers have built a network to watch for that flash of neutrinos, and help direct their telescopes for when the sky show begins. So before we get into all of the really cool science and the network itself, and I think people are going to go, wait, wait, wait, what? You see the neutrinos before you see the light from the supernova?
That’s weird. I thought neutrinos can’t, nothing moves faster than the speed of light, the supernova is moving at the speed of light. How do we see the neutrinos first?
[Dr. Pamela Gay]
So neutrinos do move slower than the speed of light. They do have mass. They are moving exceedingly fast, like it took us forever, it felt like, to figure out if they had mass or if they didn’t because their speed was close enough to the speed of light that it was within error.
We’re talking about neutrinos from galactic or near galactic supernovae, so like the Large and Small Magellanic Cloud, close enough.
[Fraser Cain]
Or in the galaxy, right?
[Dr. Pamela Gay]
Yeah, so galactic supernovae or near galactic. And because there’s a several hours lag between the neutrinos coming out and the first detection of light, that allows something moving near the speed of light to reach us before the light does.
[Fraser Cain]
Right, but why? Oh, sorry. How do we see the neutrinos before we see the light?
Like if we saw Betelgeuse go off and it’s only, say, 640 light years away, we would get the neutrinos before we saw the light from the supernova. Why?
[Dr. Pamela Gay]
It all has to do with the fact that the neutrinos are just going to fly through everything for the most part. Some will interact. Whereas it takes time for the outer parts of the star to first of all figure out they’re supposed to be glowing differently.
And second of all, for that light from inner parts of the star to escape through all that medium where it’s going to get absorbed and re-emitted and absorbed and re-emitted and get a lot of Brownian motion going on.
[Fraser Cain]
Right, right, right. I mean, we talk about this idea of this random walk that photons have to make to even get out of the sun in the first place. That when you have fusion at the core of the sun and it produces a photon of gamma radiation, that then gets absorbed by another atom.
And then that has to re-emit it, and then that gets absorbed, re-emitted, absorbed. And it can take 100,000 years from when a photon is generated at the center of the sun to when it actually reaches the surface. Now is it the same photon?
It’s been absorbed, re-emitted, and so on, but that’s the gist of the dilemma. But a neutrino, we’ve talked about this, they’ll go through a light year of solid lead, no problem. The interior of a star is nothing.
It is like glass, light shining through glass to them.
[Dr. Pamela Gay]
And the time scales for all of this happening is kind of wild. You end up with supernovae happening in a couple of different scenarios where the core of the star suddenly becomes degenerate. The one that we talk about most is iron.
The center of the star builds up into heavier and heavier atoms. It gets to the point where it has Fe, iron, in the core, and it goes to try and fuse two of these atoms together, and the atoms go high. We need to have energy added to us if you would like to do that.
Everything that’s lighter mass, you go to add them together, and they release energy. It’s at Fe, it’s at iron, where we have this sudden switch to the binding energy of the larger atom is going to need to have energy added into it.
[Fraser Cain]
It’s so shocking to me how instantaneously this happens, that up until iron, you’ve got this outward light pressure that’s coming from the interior of the star that’s pushing back against all of the mass that is trying to pull itself together. You have this balance, this hydrostatic equilibrium. As it moves up that chain of elements, you reach that point where you get to iron, and it’s like a light switch.
It just shuts off the entire star in a fraction of a second, and now suddenly there is no outward pressure, and the whole star just collapses inward. It can get up to 70% the speed of light, and it is falling into the very center of this star. It’s ludicrous.
[Dr. Pamela Gay]
One of the calculations I ran across while prepping for this show was the 5,000 kilometer across core that is iron will collapse down to about 20 kilometer across neutron degeneracy pressure supported neutron star in like one second.
[Fraser Cain]
One second. Yeah. Just boom.
All of that material is hammering the core to make that collapse, and you get neutrinos from the highest energy reactions in the cosmos. You get an enormous amount of neutrinos that are formed in this moment, and they instantly escape while, as you said, the light and the matter is trying to figure out what to do. Do I move over here?
Do you go over there? What’s going on here? Finally, you get this flash of radiation on the surface of this star that then continues to glow and grow, and it gets brighter and brighter and brighter, but the neutrinos are already gone.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
They’re already out.
[Dr. Pamela Gay]
The neutrinos are like every flavor, every style. The number of ways that neutrinos are getting created is kind of crazy. First of all, you have as the core collapses, you have the protons and the neutrons going eek, eek.
The protons with the electrons are combining. They are producing neutrons and anti-neutrinos. Then you also have some of the protons and electrons are liberating themselves because neutrons are not stable.
You have beta decay and inverse beta decay producing electron neutrinos and anti-matter electron neutrinos via both these mechanisms. Now, creating the neutron core is the easy one to think about, but you also do have the neutrons that are going back into protons and electrons periodically. Then, you also have all the thermal radiation that’s coming out where you have a ton of positrons and a ton of electrons that are going to annihilate against each other, producing light, producing neutrinos.
So, you have particle annihilation, which is a thermal production. We still don’t have any evidence of it, but there’s also theoretical concepts that photons interacting with particles could also produce neutrinos. Yeah, it’s wild, all the different things that are spontaneously going on, all because the center of the star gave up the ghost of potential energy.
It’s something like 99% of the gravitational potential energy of the star gets converted into neutrinos.
[Fraser Cain]
All right, so we understand the underlying science that we get this cool trick that we can observe forthcoming supernovae. What is the Supernova Early Warning Network?
[Dr. Pamela Gay]
It is a network of a variety of different neutrino detectors that work in a variety of different mechanisms, from water to scintillation fluid to you can actually have these things that use lead. All these different methods of detecting neutrinos at all these different sites around the world are all unified in a collaborative agreement to share data, and if they suddenly get a flux of neutrinos, and we’ve seen this before with Supernova 1987A. We have seen neutrinos from other things like neutron star, neutron star mergers.
They’re there, and if they all detect these, they should have slight timing variations. These slight timing variations are because of the path difference to each of these different places in three-dimensional space on the planet Earth. If you have enough different places with enough accurate clocks, you can figure out where on the sky to point your telescopes.
Because the neutrinos are coming out significantly hours before the photons should be detectable, there is a chance that we will be able to see a star from moment zero of light being given off.
[Fraser Cain]
This is a big unsolved mystery in astronomy, that we catch supernovae after they’ve happened. Now, there are the occasional fortunate survey where someone surveyed a chunk of the space, and then one of those stars detonated as a supernova months or years later, and then they come back around, and they’re able to compare, and like, oh, it was this star, and then it detonated as a supernova. But nobody has seen those first moments, the initial brightening, the initial flash of radiation that happens in whichever order it does.
That has never been seen before, and so the hope is on the supernova warning network. Now, we know that we got that flash of neutrinos coming from supernova 1987A, but we didn’t have the warning network, right? Right.
Like, maybe something they puzzled out long after the actual supernova had been visible in the telescopes. It was like, hmm, we see an increased amount of flux here, oh, that was coming from the supernova.
[Dr. Pamela Gay]
And let’s face it, back in 1987, neutrino detections were still new. This was still new science. We only had a few detectors in the world.
Now we have more like a dozen-ish detectors in the world, and by having more understanding, we now know that they switch identities. Neutrinos aren’t big on staying who they’re born as, so they’ll switch flavors between electron, muon, all these different varieties. They do stay either matter or antimatter.
That is locked in stone. You also have just all these different ways that we detect them again, so this is allowing us to start to see them at a variety of different energies. We weren’t there yet in 1987.
Now we’re there.
[Fraser Cain]
Mm-hmm. Mm-hmm. And so, how many neutrino events, how many supernova has the Warning Network detected?
[Dr. Pamela Gay]
Zero.
[Fraser Cain]
None.
[Dr. Pamela Gay]
It has found none. Our galaxy is being super annoying, so it is anticipated that a galaxy like ours will have a supernova about every century. So it’s not quite one per century.
That’s what you’ll find commonly written. It’s actually more like 0.8 a century, or every couple of centuries, and three a century. We should be detecting these things.
[Fraser Cain]
But when was the last bright supernova that we saw in the galaxy?
[Dr. Pamela Gay]
Kepler supernova, 1604, was the most recent. 1604 is more than 400 years ago. So they’re behind schedule.
Yeah, and so here’s the thing. If a supernova goes off in a super dusty region, we may not see it. The neutrinos will be released, so we’re now in a position to see things we couldn’t see before.
[Fraser Cain]
I mean, like the other side of the Milky Way.
[Dr. Pamela Gay]
Yeah, exactly. A lot of these star forming regions, super dense with dust, supernovas occur in star forming regions. So there is a chance there have been supernovae that we simply haven’t been able to see because they were obscure by all of the dust in the disk of our galaxy.
[Fraser Cain]
Okay, so let’s imagine that we do get a flash of a supernova. Something goes off in our vicinity. Maybe not Betelgeuse close, but 10,000 light years close.
Play this out for me. What will happen?
[Dr. Pamela Gay]
So what we expect to happen is there will be a wave of neutrinos that hit our planet passing through the planet. The detector that is closest to this incoming wave on our spherical world will detect the neutrinos first. As that wave passes through the planet hitting each of the neutrino detectors on our world as it goes through, detectors will have signals.
This will allow us to figure out the timing if everything works and all the atomic clocks are properly synced and everything else. This will allow us to figure out where on the sky to point. Now, hopefully in an ideal universe, that side is in darkness and all of the detectors on that part of the planet point that direction.
[Fraser Cain]
I didn’t even think about that. You’ve got like a 50-50 shot about whether or not it’s going to be daytime or nighttime, and so then you’re going to have to depend on the space telescopes to be able to see And what’s even worse is if it’s within 30 degrees of the sun, we can’t even point the space telescopes there because it will blast them. And that’s crazy.
You could get a flash of neutrinos that are from a supernova that goes off on the other side of the sun. It would go right through the sun, no problem, right through the earth, no problem. And we would detect it, but we can’t look at it.
I don’t know, maybe like a mission like New Horizons or something that’s in a different perspective could take a shot of the supernova, but that would not compare to the combined light-gathering capacity of the earth’s and space telescopes that we have arrayed around our planet. That would suck.
[Dr. Pamela Gay]
Yeah. Yeah. So, so there is that, that issue now, assuming that it occurs in a part of the sky where we can observe it, we get all of the, the most important at this point are the highly sensitive wide angle cameras, because we’re not going to, with a timing method, have it down to the tiny, tiny sliver of the sky that something like Hubble is able to look at.
So we’re going to need to look with the wider angle cameras. Luckily we’re starting to get more and more space-based wider angle cameras.
[Fraser Cain]
Like Euclid or upcoming Nancy Grace Roman or things like that.
[Dr. Pamela Gay]
Sphere, things like that. Yeah. So, so you look with the wider angle cameras, software says, Hey, this bright thing didn’t used to be here.
Study, study, study. The key things that we’re going to be looking for are the evolution of emission lines. The thing that generates the light in supernovae that creates that wild light curve that we’re so used to seeing is the radioactive decay of a variety of different elements.
So as you get these different transitions, this, this is where nickel is one of the great blames for supernovae light curves. For instance, this allows us to see the emission lines and it allows us to see the, the shock wave illuminated over a period of days and weeks. Now there, there are two scenarios that are possible that, that will be very interesting.
One of them scientifically interesting. The other, Oh shoot, this will allow us to explain the lack of observations for 300 years. So assume that something like this goes off night side of the planet.
Everything’s looking, everything’s looking, nothing is seen. This will allow us to say this most closely aligns with these star forming regions, all of which have massive amounts of dust in place, a limiting magnitude of if it was in these magnitude ranges, we wouldn’t have seen it. So that starts to tell us, didn’t see it.
Now the other thing that could happen is it’s theorized that you can have core collapse without having a visible supernovae. Now if you have core collapse without a visible supernovae, that, that means you can look and look and there’s no light, but you do get the neutrinos.
[Fraser Cain]
Right. So like a, like an unknown, like a star just disappearing, collapsing in on itself and it not being able to create the supernova. And that’s interesting.
I mean, we’ve seen examples of stars just disappearing from the sky and it’s been thought that maybe that’s what’s going on, that it was there and then it imploded and it was very efficient and ate its, ate the entire plate, right? And just collapsed it all into a black hole, which is mind blowing. And then that would explain why we haven’t seen the supernova maybe.
And but as you say, there would be this flash of neutrinos even though, and so that would be even more sign that we detect the flash of neutrinos. We look in the direction where it supposedly came from and there’s nothing there.
[Dr. Pamela Gay]
Yeah. Yeah. So that’s the super interesting.
[Fraser Cain]
Yeah. And then the surveys show that there’s a star missing.
[Dr. Pamela Gay]
Right. That would be great. That would be ideal.
Now, the probability of something like that happening is fairly low. This is not one of the common forms of things happening that we expect. But these are all the possibilities that the supernova early warning system is looking for and they, they have a really cool network.
It is funded by multiple funding agencies across the planet. This is international. It engages amateurs through the American Association of Variable Star Observers, which is not just Americans.
It was just named over a hundred years ago. And so there’s people out there ready for these neutrinos to be detected, ready to point in the correct swath of the sky. This is kind of like the gamma ray burst alert network that we had in, in the early two thousands when we were still trying to catch optical afterglows of gamma ray bursts for the first time.
I mean, we’ve seen them for the first time, but for like common times now, gamma ray afterglow is just like another day at the office and it’s the neutrino afterglows that we are chasing with fervor.
[Fraser Cain]
Yeah. Yeah. Yeah.
And so hopefully the next time that bright supernova, that nearby supernova goes off in the Milky Way, we will be ready. And, and the, you know, the supernova early warning network is the first step. There are other plans in the works I’ve reported on this, that they’re looking to build more powerful versions of this, more sensitive versions that you could expand outward.
And the goal would be to encapsulate Andromeda and Triangulum and try to bring more galaxies into this network. And that, you know, theoretically galaxies that we see within tens of millions of light years are giving off supernova and eventually we’ll get to this place where we’ll see them every couple of years and we will have the ability to, to watch them as they unfold. But nothing would be as, as powerful as seeing one that goes off, you know, Betelgeuse distance.
[Dr. Pamela Gay]
Yeah. And it’s all about increasing the sensitivity of these systems. When a supernova goes off, all those neutrinos fill a, they go off in all directions, assuming symmetrical supernova, you have to do that sometimes.
And so the further away something is, the smaller the cone of that sphere of neutrinos we’re going to be able to detect. By increasing the sensitivity of our neutrino detectors, we start to be able to see supernovae going off further away. We start to be able to tap into the cosmological background neutrino flux.
There’s so much cool science to come out of this and, and I’m here for it and we will be here for it for…
[Fraser Cain]
Totally.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
Hopefully, I can’t wait to report on the first detection with the, with the network. All right. Thanks Pamela.
[Dr. Pamela Gay]
Thank you, Fraser. And thank you to all of our patrons out there who’ve been there with us over and over through the years. All right.
This week, I would like to thank David Resetter, Travis C Porco, Mike Husey, Jonathan Poe, R.B. Basque, Jimmy Drake, Bob Crail, Tricor, Noah Albertson, Ryan Amari, Mike Dogg, Simeon Torfason, Mark Schneider, Michael Purcell, Jeanette Wink, Brian Cagle, Jason Kwong, Tiffany Rogers, Robert Plasmo, Laura Kettleson, Red Bar is watching. A pronounceable name. You’re welcome, doctor.
Jeremy Kerwin, Kinsaya Pamflenko, Cherisom, The Lonely Sandperson, Scott Briggs, Benjamin Carrier, Jim Scholar, Marco Arasi-Nayla, David Green, Smansky, Rando, Benjamin Mueller, Benjamin Davies, Planetard, John Drake, Bruce Amazine, Paul L. Hayden, Jeff Hornmurder, Pauline Middleink, Jordan Turner, Robert Hundell, Taz Tooley, Lee Harbourn. Thank you all so very much.
[Fraser Cain]
Thanks, everyone. And we’ll see you next week.
[Dr. Pamela Gay]
Bye bye.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by Planetary Science Institute. Audio post production by me, Richard Drumm, project management by Avivah Yamani, and hosting donated by libsyn.com. This content is released under a creative commons Attribution-NonCommercial 4.0 International license. Please share what you love but don’t sell what’s free.
This show is made possible thanks to the generous donations of people like you! Please consider supporting our show on Patreon.com/CosmoQuestX and get access to bonus content. Without your passion and contribution, we won’t be able to share the stories and inspire the worlds. We invite you to join our community of storytellers and share your voice with listeners worldwide.
As we wrap up today’s episode, we are looking forward to unravel more stories from the Universe. With every new discovery from ground-based and space-based observatories, and each milestone in space exploration, we come closer to understanding the cosmos and our place within it.
Until next time let the stars guide your curiosity!