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In 2017, astronomers detected the gravitational waves and electromagnetic radiation from colliding neutron stars. This had been long theorized as one of the causes of a certain type of gamma-ray burst. By studying the event and its afterglow, astronomers have learned a tremendous amount about the formation of the heaviest elements in the Universe.
Transcript
(This is an automatically generated transcript)
Fraser Cain [00:00:49] Astronomy cast. Episode 681 kilonova. Welcome to Astronomy Cast for 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 Doctor Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Pamela, are you doing?
Pamela Gay [00:01:10] I am doing well. I am having the meteor shower full moon sads, though this this weekend there was theoretically going to be an outburst of ETA Aquarius. And there was a full moon. Yeah, instead. Yeah, I have the full moon sads.
Fraser Cain [00:01:30] Yeah. How do we destroy the moon? How do we make this happen? I think that’s it’s important. At some point, Vantablack.
Pamela Gay [00:01:40] Can we just. Vantablack. Just paint.
Fraser Cain [00:01:42] The moon?
Pamela Gay [00:01:43] Just paint the moon black? Yeah, it’s super heated, to be fair. So all the infrared astronomers would hate us. But like us optical folks, we’d still have tides. We’d still have all the physics that we need that the moon supports Vantablack.
Fraser Cain [00:01:58] Okay, there we go. So. So before we destroy the moon, let’s just paint it black. And that will, that will and that. That way people who like tides and stuff will still be all right. Okay. Good call. In 2017, astronomers detected the gravitational waves and electromagnetic radiation from colliding neutron stars. This had been long theorized as one of the causes of a certain type of gamma ray burst. By studying the event and its afterglow. Astronomers have learned a tremendous amount about the formation of the heaviest elements in the universe. What we’ve I think we’ve talked about this before. From my perspective, the announcement and discovery of the kilonova was the best kept secret, known by about 5000 people in the field of astronomy. And like when you hear about conspiracy theories and you’re like, you know, two people can’t can only keep a secret, one of them’s dead. I was caught completely flat footed by the announcement of the kilonova. And it is my job to sense the scuttlebutt of what’s going on. You knew in advance this was coming, right?
Pamela Gay [00:03:11] I knew parts of it in advance. But the fullness of how? Basically 1 in 3 active research astronomers globally were involved in this discovery, the the sheer number and the fact that it was detected over gamma rays and optical and particle science. The fullness of the discovery was one of those things where I was like, that was bigger than I thought.
Fraser Cain [00:03:46] Every particle physicists.
Pamela Gay [00:03:47] Think.
Fraser Cain [00:03:47] Yeah, all these particle physicists, all of the people working in the gravitational wave astronomy. And then every astronomer associated with every major observatory, both on land and in space.
Pamela Gay [00:04:00] Yeah.
Fraser Cain [00:04:00] Part of these observations and part of the science paper, I’ve never seen a science paper with so many names associated with it. And those are just like the primary people from each working group, not to mention all of the other people who were involved in detecting it. Analyzing it. Yeah. It was hats off to the astronomy community for for working on this and I guess like. I guess the conspiracies are all real then. Clip that and.
Pamela Gay [00:04:32] All right, so that was the.
Fraser Cain [00:04:34] So what was the killer talk about the the event. What happened.
Pamela Gay [00:04:38] So so back in 2017, there were two neutron stars, two remnants of massive stars, but not so massive that they became black holes. These these two neutron stars, I they had been spiraling towards each other, giving off gravitational waves over time. And a that release of energy in the form of gravitational waves that causes them to spiral in towards each other. And one fateful August day, the signals of this merger occurring reached our world. And literally, I can’t say, shook it, but I can say warped it.
Fraser Cain [00:05:20] Stretched it and compressed it.
Pamela Gay [00:05:22] Yeah, yeah. So? So as these two stars, reached the point of of merging together, becoming a black hole, they released a massive amount of energy in the form of gravitational waves that were detected by LIGO. Virgo, these gravitational wave detectors on our planet, as the planet literally getting stretched and compressed in a damped harmonic oscillation.
Fraser Cain [00:05:50] Yeah.
Pamela Gay [00:05:52] It also released a whole lot of neutrons. Neutrinos, because there was a vast creation of what are called are process elements will return to that in a bit. So we had particles getting here and at the same time the, the, the first photonic signal of this was a very short blast of gamma rays that were then followed by an optical afterglow. And when I say a short burst of gamma rays, I mean it was less than two seconds.
Fraser Cain [00:06:29] Okay, so give us kind of a timeline from, from the detection of the different classes of, of waves.
Pamela Gay [00:06:40] So what’s what’s wild here is they had to piece together after the fact that that all of these things were, were tied together. So there was the almost simultaneous measurement of the gravitational waves and the gamma rays. So the first thing that happens as these stars merge is, is the flash of light and the release of gravitational energy. After this, you have these slower moving particles. Particles can’t move at the speed of light. And you also have coming afterwards the residual glow of things going on around where the merger took place. So this is the kind of event that stretched out over time, both in arrival of the information and also in being able to follow it evolve over time.
Fraser Cain [00:07:36] The thing that I find just absolutely amazing was not only did we get this, this multi-modal detection of these two of mean gravitational waves and electromagnetic radiation, but we got like the first definitive proof that gravity moves at the speed of light.
Pamela Gay [00:07:53] Yes.
Fraser Cain [00:07:53] Right. Like big question. Astronomy solved.
Pamela Gay [00:07:57] Yes. This is something that we’ve been struggling as a profession to prove for a long period of time, and we’ve gone to great mathematical and geometric ends to try and say, well, the light from this quasar was gravitationally bent in a way that indicates as Jupiter was moving, and it’s never enough proof. But when you get the gravitational waves and you get the gamma rays getting here within our ability to detect at the same time.
Fraser Cain [00:08:26] Well, and not even just at the same time, like the gravitational waves come from the last few milliseconds of the neutron stars orbiting around each other before they actually collide. That’s when you get the gravitational waves, and then moments after you get the electromagnetic radiation from their collision in the explosion. And so, you know, if the waves and the electromagnetic rays came at exactly the same time, then in fact, they wouldn’t be moving at the same speed. But because you got the the waves, then the light, it lines up perfectly. And when you think that these this light was moving hundreds of millions of light years to get to us with that level of precision. They move the same speed.
Pamela Gay [00:09:09] It. It was one of those truly amazing. All of the clocks were actually in sync kind of discoveries.
Fraser Cain [00:09:18] All right, we’re gonna talk about this some more, but it is time for another break.
Pamela Gay [00:09:23] This show is sponsored by BetterHelp. We hear all the time that it takes a village to raise a child. What folks forget to remind us is it takes a community to support an adult. I hope each of you have your own tribe, your found family, your own place where you can just go out and hang out even if it’s over a gaming server. The other thing they don’t tell you is we can all get burnt out trying to support those around us. It’s easy to get stretched thin trying to support others through all the job, money, relationship and health issues that are part of adulting. And sometimes we need to turn somewhere other than to our friend group for help. Sometimes we need someone who is outside and has that outside perspective and an arsenal of skills and tools. We don’t have to help us level up in life. This is where BetterHelp can be there for you. They’re licensed therapists, can give you tools to set boundaries or know how to better support others while supporting yourself. Whatever you need, they will help you find it, and you can switch between therapists until you find the one that is the right match for you. It’s all online and they can work with your schedule, so you never need to miss a raid or shop late to ADHD session. Find more balance with BetterHelp. Visit betterhelp.com/astronomy today to get 10% off your first month. That’s BetterHelp. H e lp.com/astronomy.
Fraser Cain [00:11:03] And we’re back. So let’s talk about this mystery of gamma ray bursts and how this helps explain what those one class of them are.
Pamela Gay [00:11:15] So. So we started discovering gamma ray bursts back in the early days of the Cold War, when there had been a nuclear test ban treaty passed that said, basically, you shall not test nuclear weapons in the air or in outer space, and to monitor whether or not that was actually happening. We launched satellites sensitive to the kinds of gamma ray light that come out during nuclear explosions, which also have our process elements. Just we’re going to still come back to that. Now, unfortunately, it turned out that for the first time ever, we discovered once above the atmosphere that there are natural sources of gamma rays. And the early detectors were not good enough to nail down what direction gamma rays were coming from. So there was a bit of, oh dear, what’s going on? That luckily, we quickly realized that gamma rays appeared to be coming from all directions on the sky in different durations. And over the years, with satellite after satellite after satellite, we’ve built up this understanding that there are essentially two broad categories of gamma ray bursts those that can last many seconds to many minutes. These are your long gamma ray bursts. And then there are the short gamma ray bursts that appear to actually break into two different groups. These are the ones that are two seconds or less.
Fraser Cain [00:12:53] Right.
Pamela Gay [00:12:54] Now. But the long ones, we we blame those on hyper nova. Astronomers shouldn’t name. Things were really, really bad.
Fraser Cain [00:13:02] Well. Are you are you kidding me? That’s the best name. Like Nova ultra Nova. Nova? Yes, please. More of that. So supernova is fine, like I. I think they nailed it. Supernova? They they got a good name out the door. They’re hyper nova. That’s just that’s just taking a win and then taking a victory lap. So I 100% agree with you when I think about the poorly named cosmological objects out there. Hyper nova. No way.
Pamela Gay [00:13:35] It’s just this feels like. How do you torture your undergrads? We have classical nova, cataclysmic variables. Nova nova, recurrent nova, hyper nova, kilonova, supernova. And then we just have letters to stuff.
Fraser Cain [00:13:51] Yeah.
Pamela Gay [00:13:52] You’re good with this.
Fraser Cain [00:13:53] Okay? Are you kidding me? Yeah. Hyper nova. Yes, yes, I’m fine with that. Not only am I fine with that, I think it is one of the best named objects in all of astronomy.
Pamela Gay [00:14:05] All right. Anyways, so there are hyper novae which produce prolonged gamma ray bursts. And there’s two general theories about what’s going on here. In one case, you have a, massive star going supernova and its mass attacks, a nearby companion that is probably a neutron star. And as it falls on to the neutron star, this creates massive jets of gamma rays. That’s one possible idea. The other possible idea is that this is simply a special kind of fast, rotating, massive star that is capable of generating these jets all on its own. Whichever scenario it is, these create massive optical after glows that we’ve been able to see since the 90s, and they’re long enough that we have time to catch them in the gamma rays, spin something around to look at them in X-rays, and zero in on where they are in the sky very successfully. These things, easy to observe in the grand scheme of hard to observe objects.
Fraser Cain [00:15:17] Because they’re just so bright.
Pamela Gay [00:15:19] Exactly. Yeah. Then the other, not a kilonova gamma ray burst is it? Looks like some of the sources that cause fast radio bursts also cause bursts of gamma ray radiation. And these can be things like highly magnetic neutron stars that are called magnetars, rearranging their magnetic field and releasing massive, short lived bursts of energy. One of these occurred back in December of 2004. It was bright enough that it passed through the sides of telescopes in between the two of these kinds of objects. This is where are two neutron. Stars coming together to produce heavy elements exist.
Fraser Cain [00:16:06] All right, hit us. What exactly is going on as these two neutron stars come together?
Pamela Gay [00:16:16] So the glorious thing about it is these stars get, to a certain degree, completely shredded as they coalesce. And and the totally disrupted neutrons there, they’re flung out during that catastrophic explosion of a merger and they hit the surrounding material. And if you take your friendly everyday atom and you bombard it with neutrons fast enough, it doesn’t have a chance to undergo what’s called inverse beta decay. This is where your typical everyday neutron is like. I don’t like to exist by myself. You take a neutron, you put it on a shelf. It’s like.
Fraser Cain [00:17:02] No, do you come back five minutes later and it’s gone?
Pamela Gay [00:17:05] Exactly. It decays into an electron and a proton. Now, if you take an atom and you bombard it fast enough with all of these neutrons, they build up, they build up, they build up, and then they switch identities. And when they do, suddenly the core of this atom goes from being your random everyday low on the periodic table atom to something crazy like Einstein M and and so this rapid release of neutrons that a salt and make themselves part of the nuclei of heavy elements in the surrounding materials allows us to get even heavier elements. And this is one of the only ways to do it. And what I love is this. This is a story that builds up over the entire lifetime over these stars. Because massive stars have massive solar winds, they blast material in all directions around them and that material hanging out around them. That’s where these heavy elements get to form. And it’s just a cool story.
Fraser Cain [00:18:13] Yeah. So you’ve got this. I mean, just think about the forces involved that you’re taking a neutron star, one of the densest objects in the universe, and you’re turning it into a neutron slurry. Yeah. As these neutron stars are coming together because of the tremendous forces involved, and then the neutrons are crashing into other neutrons, and there’s so much energy compacted in a small space that they’re just getting assembled into larger, heavier elements like gold. And this is one of them. This was one of the most incredible things. They saw Earths worth of gold in the explosion.
Pamela Gay [00:18:54] And prior to confirming the reality of these things, like they’d been predicted in the late 90s, that this should be a thing that happens out there somewhere. But when I was in grad school, I’m old. I was in grad school in the 90s and early 2000. We were taught that these heavy elements came from massive stars exploding as supernova. Add your letters and numbers after it. And and this whole idea of combining neutron stars, it wasn’t something that was just regularly taught. And now we know that the reason supernova modelers were having so much trouble in the 90s reproducing the matter we see in the universe is supernova aren’t to blame. It’s it’s these neutron stars coming together. And it’s just a really cool way that science pretty much overnight was like, yeah, and we were wrong. And right now we know now.
Fraser Cain [00:19:57] But we can’t blame all the gold on kilonova. What can we know?
Pamela Gay [00:20:01] So there is.
Fraser Cain [00:20:02] Still our process going on in some of the most heavy stars. And that is also contributing to the heavier elements.
Pamela Gay [00:20:09] It’s the overall production ratios where we have to start saying, okay, so let’s look around the solar system, let’s add up how much carbon we have, let’s add up how much iron we have, let’s add up how much technical we have. And when we make this abundance curve of of how much exists of each atomic isotope in our solar system, then we start doing the okay, so what what supernovae do you have to have go off to cause this to happen? And so you say this kind of supernova is going to produce this ratio of ingredients. This is going to produce this ratio of ingredients. And to reproduce what we see, you have to have these kilonova out there that are dedicated super heavy atom producers. And and so it’s just you need different kinds of factories producing different ratios that all together add up to the solar system we’re in.
Fraser Cain [00:21:12] Right. Right. And so now that we know about this, what role do we think that a kilonova had on the formation of the solar system and the and the gold in our wedding rings and, and electronics and things like that.
Pamela Gay [00:21:30] Well, it starts to tell us that these have been happening for a long time, and they had to exist for us to be here. I have to admit, I feel like this is one of those moments where you have read a key paper that I missed that said, exactly how many kilonova what went into our solar system.
Fraser Cain [00:21:50] So there was a kilonova. So astronomers were able to essentially estimate that the kilonova went off about a within a thousand, no thousand light years of us closer, about 100 million years before the solar system formed and delivered a tremendous amount of heavier elements into the solar system. So something within our galactic corner neighborhood in recent history, before the solar system formed. And the thing is really interesting is, is how these might be. Some of, you know, we always talk about like, what it takes to start star formation in some nebula. And now it appears that there might very well be that you could have these, these kilonova go off a seed, heavier elements, and also kickstart the process of collapse in the stellar nebula. And so at least one, probably multiple kilonova went into the formation of our solar system and gave us the heavier elements that we have all around us. And we probably wouldn’t have life on Earth in the way that we understand it without those events. So they’re, you know, they’re doom, but they’re also help with the formation of life.
Pamela Gay [00:23:08] And that’s a really cool story. One of the earliest examples that we had of what we thought might be a neutron neutron star merger was back in 2013. And the reason that they were able to say, yes, we think this is a neutron star, a neutron star merger is it occurred in a system that didn’t have significant star formation. It was old, it was elliptical. It was consistent with a old stellar population that would have fully evolved neutron stars in it. Now, if there was a neutron star, a neutron star merger within a thousand light years of the the cloud of material that we formed out of that gives you this amazing image of how old stars and unused material were mixing in the Milky Way. And makes me question. Could it have been like that kilonova or other related events from that super old population that triggered our molecular clouds collapse? And.
Fraser Cain [00:24:15] Right.
Pamela Gay [00:24:16] It’s it’s a multi-generational story.
Fraser Cain [00:24:18] So there’s a couple of of recent tweaks on top of this. One is I know if you saw the story that that researchers were able to calculate that the kilonova was a perfectly spherical explosion. Yeah, that was really interesting because you would expect like they’re coming in, as I said, the neutrons are turning into this kind of slurry as they’re orbiting on this plane. And you’d expect it to be the explosion to kind of match the collision. But in fact, the the explosion was perfectly spherical.
Pamela Gay [00:24:47] And they figured that out by looking at the black body radiation, which would have had a different distribution of life if if there had been red shifting and blue shifting and going on. But no, it was just spherical. And and what’s cool, though, is there was a slurry of material. And as some of it went out, that optical afterglow we were seeing was from some of the remainders coming back in. So you have this completely symmetric explosion, and then you have the material falling back in doing the disk thing and self-destructing as an optical afterglow on the newly formed black hole’s event horizon.
Fraser Cain [00:25:31] Now, from what I understand, there’s only been like just like maybe two more kilonova. Yeah. So, yeah, we’re at the very beginning of this science. And a big part of that is that LIGO is has been offline for the last couple of years, but it’s coming back online in just a few months from now with its next iteration.
Pamela Gay [00:25:54] And with the next iteration, we’re going to have greater sensitivity. We’re going to have. I had the chance to hopefully be sensitive to more and more of these kinds of objects, and in combination with things like the Zwicky Transient Factory, with Swift and Fermi still being healthy up in orbit. And hopefully Alice’s tea. Alice’s tea. We need to return while LIGO is still running on the next run. Or launch start return. This has nothing to do with that.
Fraser Cain [00:26:26] Yeah. But yeah, yeah, yeah. I mean, we have this incredible opportunity to do observations of an extreme event that helped deliver the essential, heavier elements into the universe. And we are months away from the next iteration of like, like, like originally they detected, like, 1 or 2 events. Yeah. Then they did an upgraded version and they were detecting one a week. And now we’ve got the new version coming out in just a few months. That should crank that up even to the next level. Several gravitational wave events a week.
Pamela Gay [00:27:07] Yeah. Yeah. The the most optimistic I’ve seen is there are hopes of maybe one a day getting noticed. Yeah. So those are the most optimistic. Yeah. I choose to be an optimist.
Fraser Cain [00:27:22] Yeah. And hopefully a new class. Yeah. Of of objects like neutron stars colliding with white dwarfs. Like maybe other parts of these gamma ray bursts that are. There’s still some controversy can go away once we do more and more of these observations. So, so stay tuned. It’s going to be an exciting year, I think. Well, thank you, Pablo.
Pamela Gay [00:27:42] Thank you. And thank you so much to everyone out there in our audience who supports us through Patreon. We we could not do this without you. You allow us to have editors that make us sound good and get everything posted up on the internets so you can download us if you would like us to. If you would like to help us support these people, please consider joining our Patreon and this will also get you ad free versions of the show. This week I would like to specifically thank Berry Gowan, Jordan Young, Steven Wright, Nano Phillips, Andrew Plasterer, Venture Trust Charlie, Brian Cagle, David Trog, Buzz Pass act, Les Howard, Laura Carlson, Robert Plasma, Jack. Mudge, Joe Holstein, Richard Drum, Greg Davis, Frank. Tippin, Gordon. Davis, Alexis. Adam and these Brown, William Andrews. Gold, Roland. Warmer, Dom, Jeff Collins, and Kellyanne and David Parker. Thank you so much, all of you out there.
Fraser Cain [00:28:42] Thanks, everyone, and we’ll see you next week.
Pamela Gay [00:28:44] Bye bye. Astronomy cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.