Episode 81: One Last Burst – Gamma Rays and Afterglows
In this episode, Jacinta chats with Dr Simon de Wet about the discoveries he made during his Master’s and PhD theses regarding mysterious gamma ray bursts (GRBs). Meanwhile, the team takes a trip back to the Pendulum Room for a final farewell to the old studio.
Above: Dr Simon de Wet
Gamma Ray Bursts are some of the brightest bursts of high energy light in space, usually originating from the collapse of a massive star or two neutron stars colliding. Both of these processes create a black hole, which ejects very bright light into space. GRBs happen frequently, but far away from us!
Above: The optical afterglow to GRB 220427A as the faint source at the centre of the green circle. Image credit: Simon de Wet PhD thesis
Simon has begun his post-doc in Copenhagen where he will continue working on transient astronomy. Transient astronomy involves studying objects that vary in their nature. Simon talks us through the accidental discovery of GRBs, how we discovered that GRBs are from very distant galaxies. He also mentions that GRBs originate from collapsing stars as well as the formation of a black hole.
Simon’s PhD work focused on trying to capture the optical afterglow of GRBs using the MeerLICHT telescope in Sutherland. He found that the light curves of the optical afterglows observed did not behave as expected. Simon used radio data from MeerKAT, ALMA in Chile, ATCA in Australia and GMRT in India where radio afterglows were observed.
Above: MeerLICHT telescope. Image credits: SARAO 2018
Related Episodes
https://thecosmicsavannah.com/episode-73-african-skies-and-supermassive-black-holes/ – Dr Eli Kasai discusses his work on blazars using SALT and the Cherenkov Telescope Array.
Acknowledgements
Podcast Manager: Francois Campher
Podcast Assistant Manager: Kaashifa Saloojee
Social Media Manager: Sumari HvN
Transcript: Sisa Shibane
Audio Editing: Nick Rushton
A big thank you to Visual Pill Productions for filming this episode!
Above: Visual Pill Productions team (left to right): Reece Brice, Rizwaanah Saloojee, Salvadore Marcial.
Transcript
[00:00:00] Daniel: Welcome to The Cosmic Savannah with Dr. Daniel Cunnama,
[00:00:08] Francois: Francois Campher,
[00:00:09] Jacinta: and Dr. Jacinta Delhaize. Each episode will be giving you a behind the scenes look at world class astronomy and astrophysics happening under African skies.
[00:00:18] Daniel: Let us introduce you to the people involved, the technology we use, the exciting work we do, and the fascinating discoveries we make.
[00:00:25] Francois: Sit back and relax as we take you on a safari through the skies.
[00:00:30] Jacinta: Hi everyone. Welcome to today’s episode.
[00:00:32] Francois: Hey Jacinta.
[00:00:33] Daniel: Hello.
[00:00:34] Francois: Hi.
[00:00:35] Daniel: And yeah, just to turn announce we are for those listening online, we are back in the original studio that Jacinta and I began this whole thing in and yeah. Wave to the camera if you’re watching online. Yeah our tiny little studio, I think some of you may have seen it on social media a long time ago. We’re in sitting inside the old pendulum room at the SAAO and in a tiny little dusty room.
[00:01:00] Jacinta: It’s very different to the one button studio that you if you’ve been watching on YouTube, the last few episodes you’ll have seen we’re back in our roots just for no soldier’s sake and we very kindly have some amazing videographers who have volunteered to join us today, and they have hitched a camera up somehow magically to a… like metal rod in the roof and it’s a very wide angle lens because this room is teeny, teeny tiny.
[00:01:26] Daniel: Yeah.
[00:01:27] Jacinta: Anyway, so that’s where we are, Tshiamiso is unfortunately not able to join us today but that’s kind of fortunate because we can’t fit four people in here. But anyway, so the One Button Studio is all booked out. That’s why we’re in here.
[00:01:39] Francois: Well-
[00:01:40] Daniel: Yeah, also I think like Francois said a nice farewell to the pendulum room.
[00:01:44] Francois: It is, but we might need to use it again, so I dunno if it’s a farewell.
[00:01:49] Daniel: Okay.
[00:01:50] Jacinta: Anyway, so today’s episode we are talking with Dr. Simon De Wet, who is- who works on gamma ray bursts, and he’ll tell us all about he, what he found out during his PhD.
[00:02:03] Daniel: So Simon has now moved to?
[00:02:05] Jacinta: Copenhagen
[00:02:06] Daniel: Copenhagen? Okay. Where he’s doing a postdoc?
[00:02:08] Jacinta: Yes. Yes. Yep.
[00:02:09] Francois: Had DTU. He is I believe he’s studying transients now. So, Supernova mainly, but in today’s episode we’ll mostly be talking to him about his PhD and Master’s work, which is all on gamma ray bursts.
[00:02:23] Daniel: And who wants to go first?
[00:02:25] Jacinta: Okay, well, I’ll, I’ll ask the questions here because I dunno anything about gamma ray bursts? So right. First of all. I’m gonna ask Francois first because I know Francois works on transients and don’t, gamma ray bursts are classified as transients. I’m gonna assume so. GRBs gamma ray bursts. Francois, what is a GRB?
[00:02:46] Francois: A GRB is basically a incredibly bright burst of light energy from space. That is the, usually the result of either a collapse of a very massive star, which is like 20 times the mass of the sun, or of what? Well, we think it is the, also, it could be caused by two neutron stars orbiting each other and eventually colliding, forming a black hole. So basically in both cases, a black hole is formed and from this violent formation these incredibly bright bursts of light get shot into the universe. And when I say bright, okay I read this like last night about GRBs they basi- like the average GRBs amount of light that produces is equal to the total light of the sun over its 10 billion year long lifespan.
[00:03:44] Jacinta: Whoa!
[00:03:45] Francois: Yeah. Like if you add up all of the energy that the-
[00:03:48] Jacinta: Sun ever emits, ever?
[00:03:49] Francois: Yes, and that’s, that’s the average energy of A GRB.
[00:03:52] Jacinta: What? In like two seconds or something?
[00:03:54] Francois: Yes, in two seconds. Wow.
[00:03:55] Daniel: But then that’s obviously spread over a huge distance, which is why we can see them from very far away.
[00:03:59] Francois: Yes, exactly.
[00:04:00] Daniel: So when these gamma ray bursts are happening and we are observing them, they’re things which are happening very far from us. Not like the sun.
[00:04:06] Francois: Yeah incredibly far. Yeah that’s why we are all alive. They are all so far, at least most of the ones that we’ve discovered are decently far away enough so that the ozone layer can protect us from the gamma ray bursts. In fact, gamma ray bursts happen quite frequently. We see at least one, about one or two. I think a day is the average detection.
[00:04:28] Jacinta: Oh really?
[00:04:29] Francois: It depends, but the frequency is quite high. So basically in space, your chance of surviving has gone down. Again. I know it’s low already, but to this point it is impossible. Right so luckily for us, we have an ozone layer which protects us from these, the gamma ray bursts mostly. However that is only because they are decently enough far away, so the light is spread out enough for it, the ozone layer to protect us. But if one were to go off within our like galactic neighborhood, well we’d be done for basically.
[00:05:07] Daniel: It’ll be quick.
[00:05:08] Francois: Yeah, exactly. Yeah and we won’t know until it happens! So that’s fine.
[00:05:11] Daniel: Well, yeah and then you won’t know any either. Yeah basically you’ll never know. Pretty much and but, so detecting these gamma rays we can do that from earth.
[00:05:23] Francois: Yes.
[00:05:23] Daniel: But as you said, the ozone stops them. So what happens is you set up these arrays these gamma ray telescope arrays which detect the cascade of highly charged particles. So the, the gamma ray hits the ozone layer the upper atmosphere and explodes into, you know, well explodes, splits into many different particles. Which then cascade down to the surface of the earth and we kind of reconstruct that car crash to work out where, where the thing came from.
[00:05:53] Jacinta: So what kind of tele- like is it an optical telescope or like what kind of telescope detects though that cascade?
[00:06:00] Daniel: So in terms, so these gamma ray bursts are coming into the upper atmosphere, as you said, like they’re hitting the ozone layer and the particles there. So then it’s a question of how we detect them. So in space a gamma ray telescope in space can detect them, you know using regular, well not regular, but like a gamma ray telescope and it’s detecting the, the actual gamma ray light. But because the gamma rays don’t pass through the atmosphere, we have to build these arrays of detectors of the, of the secondary light.
[00:06:32] So what happens is the gamma ray hits the upper atmosphere and it passes its energy into, to a series of a cascade of particles which then come down towards earth and those particles emit glow, like a, a blue go glow. So then, you know the telescope can detect all of these particles and reconstruct the car crash that happened as the thing, hit the upper atmosphere and try and work out which direction it came from.
[00:07:01] Jacinta: Yeah, we talked about that a bit in a previous episode with Dr. Eli Kasai from Namibia about HES- the high energy? Oh? High energy, ste-reo-scopic?
[00:07:14] Daniel: Yeah ’cause it’s stereoscopic, right? Stereoscopic. Yeah. It’s stereoscopic. So that it can yeah, it can work out the direction right.
[00:07:20] Jacinta: So, sorry I’ve temporarily forgotten, but check out that episode we, we’ll link it in the show notes and that was also in preparation for the CTA Cherenkov Telescope Array which is gonna be built in the future. And you may notice if you’re watching this on YouTube that I’m no longer wearing headphones and now Francois…
[00:07:38] Francois: yeah, that’s a good point.
[00:07:39] Jacinta: is wearing the headphones of shame. Because he’s new to the studio recording in here and he’s making too much noise. So now we’ve given him the headphones so he knows when he is making too much noise. I also continually forget that we’re like being recorded on video right now because we never have video in the studio. So I keep doing things like.
[00:07:55] Daniel: Yeah, like pointing to the mic.
[00:07:57] Francois: That’s great.
[00:07:57] Daniel: It’s good, it’s good for the viewers. So if you’re listening online, maybe go back and look for that.. Also like Jacinta’s hair after taking off the, the headphones is…
[00:08:05] Jacinta: oh no! Give me my headphones back! Are you joking or are you serious?
[00:08:12] Daniel: I’m serious. Of course, I’m serious. Okay. But let’s, I mean, maybe we should actually get into Simon’s interview before we rattle too much on gamma Rays.
[00:08:23] Jacinta: Yes. Simon did his PhD on on GRBs, and he’s the expert. So yeah, let’s just, let’s just hear from him.
[00:08:35] With me now is Dr. Simon Devet from the University of Cape Town. Welcome to the cosmic Savannah Simon.
[00:08:41] Simon: Hi. It’s great to be here.
[00:08:42] Jacinta: Tell our listeners a little bit about who you are, where you’re from, what you do.
[00:08:47] Simon: Yeah, so I was born and raised in Cape Town. I’ve done all my studies here at the University of Cape Town and I’m an astronomer.
[00:08:55] Jacinta: Yes you are! Simon, you have just gotten your PhD in astronomy from UCT, so you are, you have been one of our PhD students in the Department of Astronomy at the University of Cape Town and you’ve submitted your PhD thesis after years of very, very hard work and your thesis examiners passed it and you’ve just had your graduation ceremony. So now you are officially doctor. Congratulations.
[00:09:24] Simon: Thank you. Yeah, it’s a great achievement. I’m re and I’m very proud of it.
[00:09:27] Jacinta: You should definitely be. How was your graduation ceremony?
[00:09:31] Simon: No it was, it was just a fantastic day, really. A lot of, lot of smiles, a lot of happiness. Yeah and also a lot of relief.
[00:09:37] Jacinta: I was gonna say, surely relief as well yeah. So Simon, today you are here to talking with us in the studio what do you think of our studio?
[00:09:49] Simon: I really like it. It’s a nice quiet room. It’s a good place to do some research.
[00:09:54] Jacinta: You reckon? I’ve never thought of that actually. It’s a very, it’s a very strange place, but a very cool place and we are really glad to have caught you for an interview now, because in a couple of days you’re actually flying off to another country to do your, to take up your first postdoctoral research job.
[00:10:15] Simon: That’s correct. Yeah, on Sunday I’m going off to Denmark and I’ll be doing a three year postdoc at DTU in Copenhagen, the Danish Technical University. I’m very excited for that.
[00:10:24] Jacinta: Wow. So you’re moving to Copenhagen for three years?
[00:10:27] Simon: That’s correct.
[00:10:28] Jacinta: Wow, that’s so exciting. What will you be doing there?
[00:10:33] Simon: Yeah, so I’ll be continuing within time domain astronomy or transient astronomy, which is the study of objects in the night sky, which vary over a range of timescales.
[00:10:45] Jacinta: So things that go bang in the night basically.
[00:10:47] Simon: Exactly.
[00:10:48] Jacinta: Things that suddenly glow brightly, which weren’t glowing before.
[00:10:51] Simon: Exactly.
[00:10:52] Jacinta: Okay. Awesome. So you’re gonna continue with that research in your first postdoc, so that’s what you were working on for your PhD can you tell us a little bit more about what you were doing?
[00:11:04] Simon: Sure. So over the course of my PhD I was studying a particular category of explosion called gamma ray bursts. These are, I guess they claim to fame is that they are the brightest explosions in the night sky and they really are fascinating. I can talk for a long time about them.
[00:11:20] Jacinta: Well that’s good because that’s what we’re here to do. So GRBs gamma ray bursts I don’t know where to start. What are they?
[00:11:30] Simon: Yeah, so gamma ray bursts are essentially the brightest explosions in the night sky. And one should look to the name to see where yeah, what these objects are. So gamma rays are the highest form of electromagnetic radiation, the highest energy form of EM Radiation.
[00:11:45] Jacinta: So they’re a kind of light, right?
[00:11:47] Simon: Exactly.
[00:11:47] Jacinta: So optical light is a kind of electromagnetic radiation. And how does that differ to gamma rays?
[00:11:54] Simon: Well, yeah, so optical light is also em radiation, but it’s much lower energy.
[00:11:58] Jacinta: Mm-hmm.
[00:11:59] Simon: So gamma rays are, they can actually penetrate through all kinds of materials, which makes them very, very harmful.
[00:12:05] Jacinta: Mm-hmm. So they can be harmful to humans.
[00:12:08] Simon: Indeed.
[00:12:08] Jacinta: Okay. And these gamma ray bursts, are they harmful?
[00:12:12] Simon: They would be if they were very nearby, for instance, in our galaxy. But most of them, pretty much all of them that we have observed have been in very distant galaxy. So we don’t have to worry too much about them actually harming us.
[00:12:23] Jacinta: So do we think that gamma ray bursts have ever gone off in our galaxy the Milky Way?
[00:12:28] Simon: Well, it’s actually quite interesting. Some people have put forward theories that say that some of the very large mass extinctions on earth were in fact caused by gamma ray bursts.
[00:12:38] Jacinta: Really?
[00:12:39] Simon: Indeed, yeah.
[00:12:40] Jacinta: Oh wow. Okay. So wait, what does that mean? Are we in danger?
[00:12:45] Simon: Well, if one did go off an our galaxy and was pointed right towards us, yes, we’d all be toast.
[00:12:50] Jacinta: Oh dear. Okay alright, so then wow, that was, that was blowing my mind. All right, so these are bursts of gamma rays, as the name suggests. Alright. So how were they discovered? Maybe let’s start there.
[00:13:06] Simon: So they were actually discovered by accident in the 1960s. So what happened was the the Americans put up a whole lot of satellites into space, and these were called the Vela satellites and they were launched to, with gamma ray detectors aboard to see whether the Soviet Union, the Russians, were actually keeping to their part of the nuclear test ban treaty. Because a nuclear test on earth would emit a whole lot of gamma rays that would be detectable by these satellites. So it was actually for almost espionage that they were sent up into space. And then, after a few years they discovered these mysterious bursts not coming from earth, but coming from space.
[00:13:49] Jacinta: Oh, and did they think it was atomic? Bombs or anything to begin with?
[00:13:54] Simon: Well, they knew that it wasn’t atomic bomb because an atomic bomb test has a very particular, signature which is quite different from the bursts that come from space.
[00:14:06] Jacinta: Okay, so they were coming from space. So then what did they find?
[00:14:10] Simon: They detected a very bright gamma ray sauce that would last for around a few tens of seconds. Over a few years, they detected quite a few of them coming from quite random parts of the sky and essentially for the first 30 years of, the fields of gamma ray bursts, people really didn’t know where they were coming from, where they’re coming from within our galaxy or where they’re coming from much further away.
[00:14:34] Jacinta: Right? Because, so they were seeing these sudden flashes of gamma rays lasting up to tens of seconds. We can see where they are on the sky, but we don’t know like distance, ’cause distance is so hard to study in astronomy and to to understand distances in space. So they could have been close to us in the Milky Way, but they could also have been from galaxies far, far away.
[00:14:58] Simon: That’s correct.
[00:14:59] Jacinta: And what was the answer?
[00:15:01] Simon: Well it, like I said, it took 30 years for us to actually figure out where these gamma rea gamma ray BOATs were coming from and that was due to the discovery of the first counterparts at other wavelengths in particular at optical wavelengths.
[00:15:17] Jacinta: So when you say counterpart, what does that mean?
[00:15:20] Simon: That means you see, an object at the position of the gamma ray burst, but at a particular wavelength or energy. For instance, at radio waves, x-rays or an optical light, you see light coming from essentially the same source.
[00:15:37] Jacinta: Okay? So from the same position as where the gamma rays went off, you see suddenly you see a glow, or in the optical you see a glow in the radio and, and all of these other wavelengths of light. Okay? So this is called the. Afterglow, is that correct?
[00:15:53] Simon: That’s correct.
[00:15:54] Jacinta: And it, so presumably from the name it comes after the gamma ray burst went off?
[00:15:59] Simon: Exactly. Yeah. So they, they’re these two types of lights that I guess come from gamma, gamma ray bursts. So you have the prompter mission, which is the gamma rays itself, and then very shortly thereafter you get the afterglow, which is radiation or emission from across the, the electromagnetic spectrum.
[00:16:17] Jacinta: Alright, so quick flash of gamma ray bursts and then after that then this glow at the other wavelengths. So you said it took them 30 years to figure out where these gamma ray bursts were coming from and that happened once they found these, after glows. Why was that important?
[00:16:32] Simon: The reason it took 30 years was that it was very difficult to localize gamma ray. It was very difficult to find out where exactly in the sky they were coming from and that is due to the gamma ray detectors themselves which are rather crude. In terms of, yeah, localizing the source of gamma rays, which is in contrast to say an optical image of the sky where you have very high resolution and you can separate objects nice and clearly.
[00:17:01] Jacinta: Okay, so when you say localize, you mean to know exactly where it was coming from. So you might see gamma rays in like, roughly that broad part of the sky, but you’d need something with a much higher resolution in order to figure out like to have a much smaller area to localize it to a much smaller area on the sky, therefore, knowing exactly where it’s coming from.
[00:17:24] Simon: That’s ex, that’s exactly right.
[00:17:25] Jacinta: Okay. And so an afterglow was discovered what? First with the optical, an optical telescope?
[00:17:31] Simon: Well, actually, the first afterglow was discovered at x-ray energies. But then a few months later, they discovered the first optical afterglow.
[00:17:39] Jacinta: All right. And then, so what did that tell us?
[00:17:42] Simon: Well, once you detect something in the optical, then you really can, precisely pinpoint its position. The optical light is really valuable because if you get take a spectrum of that optical source, you can actually figure out the distance.
[00:17:57] Jacinta: Right? And a spectrum is when you use a telescope and you split the light into tiny little chunks in frequency or in wavelength and then you can see particular features like what we call absorption lines. So basically you have gas and stuff absorbing some of the light. It’s a tiny little frequency ranges and if you can see exactly, what frequencies these are happening at it tells you the distance.
[00:18:25] Simon: Exactly.
[00:18:26] Jacinta: So by looking at this, this optical afterglow that helped to pinpoint the position. So then they know, okay, let’s point this other optical telescope, with this spectrograph at that position, we can get the spectra then, then they found the distance.
[00:18:40] Simon: Exactly. Yeah.
[00:18:41] Jacinta: And what was the distance? What did they find?
[00:18:43] Simon: So what they discovered was that these gamma ray bursts were not coming from our own galaxy. They were actually coming from very distant galaxies in the universe at pretty high redshifts, I would say.
[00:18:54] Jacinta: Okay. So not in the Milky way. Very high Redshifts. Meaning very, very far away?
[00:18:59] Simon: Indeed.
[00:19:00] Jacinta: So then they know that the GRBs, the gamma ray bursts are originating. Very far away. What do we actually think, is causing the gamma ray burst, like physically, what’s happening?
[00:19:11] Simon: Yeah, so I guess shortly after those very first afterglow discoveries, they noticed for a few, gamma ray bursts that there was a supernova associated with the burst and what that, allowed us to tell was that. The core collapse of like a very massive star is in fact related to the long gamma ray bursts.
[00:19:35] Jacinta: Okay? So massive stars at the end of their lives. They die in huge supernova explosions. So the, it is called a core collapse because the whole. Star collapses in towards the core and even the core, like the center of the star itself collapses and then stuff rebounds in this big supernova explosion and what can be left at the end of that is a black hole.
[00:19:57] Simon: That’s right. Yeah.
[00:19:59] Jacinta: So since you saw supernova go off at the same position as the gamma ray burst and kind of shortly after, so then the conclusion is that GRBs maybe are caused by this collapsing star in the formation of a black hole.
[00:20:12] Simon: Indeed.
[00:20:13] Jacinta: Cool.
[00:20:15] Simon: Yeah, no, they’re related.
[00:20:16] Jacinta: All right. So gamma ray bursts caused by the formation of a black hole. And do we know any more details about like what physically happens when this black hole’s formed to create this gamma ray burst?
[00:20:28] Simon: Sure. So our current best physical picture is that after the collapse of the star, you have a black hole and materials surrounding that black hole falls into the black hole and it creates this very strong, outflow or blast wave that is emitted from the black hole in two directions, and within that blast wave you have light being emitted and that is what we see as the gamma ray burst and also the afterglow. Yeah and that’s the fireable shock model.
[00:21:02] Jacinta: Cool. That’s a cool name. Fireball Shock model. Okay, so now we know where GRBs come from and we have an idea of what’s producing them. So what did you do in your research during your PhD?
[00:21:15] Simon: Yeah, so the aim of my PhD work was to follow gamma ray burst and try and catch their optical after glows. In particular, I used the MeerLICHT optical telescope, which is at Sutherland here in South Africa. A really great little telescope which is very good at observing explosions, yeah.
[00:21:37] Jacinta: Cool. and yeah, tell me what you did with MeerLICHT.
[00:21:41] Simon: So MeerLICHT, because it’s fully robotic and it has six optical filters, we are able to rapidly point the telescope, to the position in the sky where gamma ray burst has just gone off and obtain really nice optical data.
[00:21:58] Jacinta: Okay and What did you find?
[00:22:02] Simon: So over the course of my PhD, roughly two and a half years for which this program was running, we followed up I guess 29 gamma ray bursts, but in total we saw 10 after glows.
[00:22:15] Jacinta: Oh, cool. So you had a look at 29, gamma ray bursts that had gone off detected, presumably with gamma ray telescopes, and then you went to those positions with MeerLICHT and you were like looking to see if you saw any matching glow in the optical. And you saw it for, what did you say? 10?
[00:22:31] Simon: Yeah, I think roughly 10.
[00:22:32] Jacinta: Cool.
[00:22:33] Simon: About a third.
[00:22:33] Jacinta: And was there anything interesting about it that you observed?
[00:22:36] Simon: So we used MeerLICHT to track the brightness of the object as it evolves in time. And, you know, there’s kind of like a standard light curve that one expects but we observed some really unusual behavior for some of these bursts, and that’s why we were able to write a publication.
[00:22:54] Jacinta: Okay, so we have an idea of how bright this optical afterglow should be and how that should change over minutes and hours, like once you first spot it and it changes very, very quickly, and you observed that it wasn’t quite changing the way that we expected it to, right?
[00:23:16] Simon: That’s correct. Yeah so a bit, a big challenge of the follow-up of these gamma ray bursts is that. They evolve very quickly. So you rarely need to get on sky very quickly to, to see how it’s changing before it fades too much.
[00:23:29] Jacinta: So it’s a, it’s a game of speed, basically.
[00:23:33] Simon: Absolutely.
[00:23:34] Jacinta: Okay. So, so MeerLICHT and you use MeerLICHT in Sutherland, it can like. This burst goes off, there’s an alert that goes around and then MeerLICHT’s able to like look really quickly at that point and be like, look I got there really fast, and so then as soon as you get there, then it’s already, the amount of light is starting to change really quickly and so that was your advantage is like you got to spot what was going on, just shortly after the gamma ray burst. Right?
[00:24:01] Simon: Exactly.
[00:24:02] Jacinta: So this unusual what you call a light curve, this changing pattern of the brightness, what does that mean? what does that mean?
[00:24:12] Simon: Well, if we see something unusual, it’s, for one thing, it definitely requires further study. We want to know exactly what’s going on with this explosion. Are there, are there different physics at play? You know, what’s going on with the, with the collapsed star?
[00:24:27] Jacinta: So to be continued, right? We don’t know yet.
[00:24:29] Simon: No. So at this stage in the field, we want to observe as many gamma ray bursts as we can so we can put together the clearest picture we have of the physics of these explosions.
[00:24:39] Jacinta: Right? ’cause this is a really quite a new research field, isn’t it?
[00:24:42] Simon: I guess it started in 1997, and it really ramped up in 2004 with the launch of Swift, an amazing small NASA mission.
[00:24:54] Jacinta: Telescope to detect gamma bursts. Yeah?
[00:24:56] Simon: Exactly.
[00:24:57] Jacinta: Cool. So, yeah, this is a, it’s a really exciting field and, not that many observations and so your contributions are really, you know, providing what we call observational evidence. We just need to, we need to observe them and we need to observe them as quickly as possible, and for as long as possible and see what happens. So it’s like providing more observational evidence so that hopefully we can build our physical models over time and try and understand the physics of what’s going on, in these systems. And you mentioned there was something else interesting about one of the, after glows you saw.
[00:25:32] Simon: Yeah, so the last burst, which ended up as a publication was really interesting because we got a whole host of radio data, including with the Meerkat Radio telescope, which is also here in South Africa and the one of the most sensitive radio telescopes in the world.
[00:25:47] Jacinta: Oh, my favorite telescope is what I use for a lot of my research. Okay, so. We know you can have after glows in the x-rays, we know you can have after glows in the optical and so now you can have also after glows in the radio.
[00:25:58] Simon: Yes. And in fact I would say even to this day our understanding of radio afterglow emission is still in its infancy.
[00:26:08] Jacinta: Alright. So we don’t understand why it’s there.
[00:26:10] Simon: Mm-hmm. Exactly. So I mean there are not as many bursts that are actually followed up at radio wavelengths. Also, they need to be quite bright for there to be radio emissions, so that’s what makes it quite challenging.
[00:26:23] Jacinta: Okay. So you provided some more observational evidence by also getting the radio after glow. Was there anything interesting about it or we don’t really know yet?
[00:26:31] Simon: Yeah in fact it was a very unusual and interesting radio data set. So we got millimeter data with the Elmer Array, which is in Chile and by far the most sensitive millimeter, observatory in the world. And then we also got radio data from ATCA Australia Telescope Compact Array. Then MeerKAT, like I mentioned, and also a telescope in India called the GMRT, the Giant Meter Wave Radio Telescope.
[00:27:02] Jacinta: Cool. So you got radio data from all over the world. Did you find anything interesting?
[00:27:07] Simon: Yeah, so what was really unusual was actually at millimeter wavelengths in the Elma data, we saw this very strange re-brightening, which has never been observed before. And so it was my job to try and explain you know, using physics arguments what exactly is going on?
[00:27:25] Jacinta: I know this might be a bit advanced, but what, what did you find, what did you, what did you, what do you think was the reason?
[00:27:31] Simon: Well, what often happens in science is that there’s no conclusive, you know, there’s no very firm conclusion. But I did put forward a few different explanations. One was that it could be, a reverse shock, you know, a blast wave or a shock wave moving back-
[00:27:48] Jacinta: oh, towards the black hole.
[00:27:49] Simon: The black hole.
[00:27:50] Jacinta: Okay.
[00:27:51] Simon: Yeah.
[00:27:51] Jacinta: So that’s your best guess is like this kind of reverse blast wave.
[00:27:55] Simon: Exactly.
[00:27:56] Jacinta: Cool. That’s really awesome. Well, that is all extremely interesting, Simon. Thank you so much for taking the time, especially in this busy period just before you immigrate to a different country to speak with us and explain this really cool new field of, astronomy to us. And before you go, do you have any final messages for listeners?
[00:28:17] Simon: Yeah, I guess, you know, based on my own experience I just really encourage everyone if you really are passionate and interested about something just go full on into it because it really can be so, so, so very rewarding.
[00:28:30] Jacinta: Awesome. So throw yourself all the way in. Yes, again, congratulations on getting your PhD, your achievements and for speaking with us today. Thanks very much, Simon.
[00:28:41] Simon: Thanks very much.
[00:28:47] Jacinta: So, I thought it was really interesting hearing from Simon. A few things blew my mind, including that many of the mass extinctions on earth may have been caused by gamma ray bursts.
[00:28:56] Daniel: I didn’t know that.
[00:28:57] Jacinta: I did not know that either. Yeah. I mean, that matches what you were saying at the start, Francois, about how if something went off close to us, we’re in trouble.
[00:29:05] Daniel: Yeah yeah. We’d be toast.
[00:29:06] Jacinta: Yeah.
[00:29:07] Daniel: Yeah and I mean, I imagine the you know, things like the upper atmosphere the constant, like what it’s made of has changed over the years. So maybe we’ve gone through periods where it’s been slightly less protective. I mean, I don’t know how it would play out, but I mean, I know how the once off event would play out.
[00:29:22] Francois: Yeah, would be quick.
[00:29:24] Daniel: Fried! But a mass extinction event where like something survive. Anyway, this is not our area of expertise.
[00:29:30] Francois: No, not at all.
[00:29:31] Jacinta: Microbes would survive and have survived.
[00:29:34] Francois: Yeah. Some of them. I think that-
[00:29:36] Daniel: and we start from scratch again. Oh!
[00:29:37] Jacinta: Extremophiles yeah.
[00:29:39] Daniel: Man, we go back 4 billion years. Oh! All that effort.
[00:29:43] Jacinta: Oh yeah. Simon was talking about. One particular type type of GRB is called long GRBs right?
[00:29:50] Francois: Yeah.
[00:29:51] Jacinta: But if I understand correctly, there’s also short GRBs. Is that correct, Francois?
[00:29:54] Francois: Yes. So long is a relative, relative term long, just usually means greater than two seconds. Whereas short is less than two seconds. So short, GRBs we think are caused by neutron star mergers and they are therefore slightly shorter in duration usually. Lower than two seconds, but more often than not in the millisecond range of time for which they last.
[00:30:23] Daniel: One thing I forgot to mention earlier, which I saw just the other day, they detected the first, repeating one. So the whole idea with the gamma ray burst is like, maybe it’s a star going supernova, or it’s two neutron stars merging and these are what, once off events?
[00:30:40] Francois: Mm, typically.
[00:30:41] Daniel: So they had one which repeated. Three times.
[00:30:44] Jacinta: What? Three times?
[00:30:46] Daniel: Three times. So like, they witnessed it and then it was, I think it was in the space of a few hours it went three times. So that, obviously we love these things because we have no idea what it is but the idea is potentially it’s a star getting devoured by like an intermediate mass black hole.
[00:31:06] Jacinta: Oh!
[00:31:06] Daniel: In which case it’s not happening in one go. It’s like, like getting, like coming in clumps, being in eaten in clumps.
[00:31:13] Jacinta: Wow.
[00:31:13] Daniel: So like merging in clumps rather.
[00:31:15] Jacinta: So that’s incredible for multiple reasons ’cause we’ve never actually detected an intermediate black hole before.
[00:31:20] Daniel: No, exactly.
[00:31:20] Francois: That’s that’s a good point.
[00:31:22] Jacinta: That’s, that’s theoretical, right?
[00:31:23] Daniel: Yeah.
[00:31:24] Francois: Yeah.
[00:31:24] Jacinta: That’s cool.
[00:31:24] Daniel: Yeah yeah. It’s great. It’s like, you know, like there’s levels of excitement.
[00:31:28] Jacinta: The short gamma ray bursts are caused by something slightly different to the long gamma ray bursts. Right? So the long gamma ray burst, as Simon was saying, you’ve got this fireball model and you’ve got like the jets and shock from a collapse collapsing, star forming a a black hole but then the short burst that’s caused by something different. I have two favorite GRBs. The first one is the one that was detected at the same time as a gravitational wave.
[00:31:56] Francois: Yeah, of course.
[00:31:56] Daniel: Yes. Well, that’s everyone’s favorite.
[00:31:58] Francois: 2017 yes. The simultaneous detection of those two things is ridiculous considering how difficult it is to detect gravitational waves and also the fact that. Like you were saying earlier, they basically just turned it on.
[00:32:13] Daniel: Yeah.
[00:32:13] Francois: And that they detected it.
[00:32:14] Daniel: So, so a bit of background for those who aren’t aware of it, we definitely covered this previously but in 2017, there was the first ever detection of two neutron stars merging by a gravitational wave detector and simultaneously for the first and now only time, there was electromagnetic counterpart, which means normally when you get a black hole merger or a a gravitational wave merger. Because they’re black holes, there’s no light escaping. But in this case, the resultant merger presumably isn’t a black hole, or wasn’t initially. So a lot of the light escaped. So we witnessed thing this first in a gamma ray burst, and then it cascaded through the energy spectrum it was witnessed by salt, observed by SALT and various other things. Very exciting event in 2017. Everybody absolutely lost it and yeah, so, and then, yeah as you were saying, like they had sort of just turned LIGO on really for this and witnessed it and it was, at the time, they, it was calculated to be like a once in 40 year event, and it happened within like a couple of months. Now it’s been eight years and we haven’t seen another one so…
[00:33:24] Jacinta: think too soon right? Beginner’s luck. Wow.
[00:33:27] Daniel: Beginner’s luck yeah.
[00:33:28] Jacinta: But that was cool and then that basically proved how a whole bunch of the elements in the universe were formed, right?
[00:33:33] Daniel: Yeah yeah we ticked a whole lot of questions, yeah.
[00:33:34] Jacinta: Gold and platinum.
[00:33:36] Daniel: Like entire fields of astronomy just died that day. Ticked. Done.
[00:33:40] Jacinta: Solved. Moving on. Go get another job. And then my second favorite is BOAT.
[00:33:49] Francois: BOAT?
[00:33:50] Jacinta: BOAT. B-O-A-T, Brightest Of All Time.
[00:33:54] Daniel: Yes, the Lionel Messi of gamma ray bursts.
[00:33:57] Francois: Yeah.
[00:33:57] Daniel: That thing.
[00:33:57] Francois: GOAT. So the BOAT yeah, the BOAT was, it’s yeah nicknamed the BOAT ’cause it was the brightest just thing ever observed. It was in 2022, in October of 2022, and it fried some of the detectors that were used to detect how bright was.
[00:34:18] Jacinta: Because it was so bright. ?
[00:34:19] Francois: Yes.
[00:34:19] Jacinta: Insane.
[00:34:19] Francois: And it also caused a slight resonance in the ozone layer.
[00:34:23] Jacinta: What?
[00:34:24] Francois: Yeah it-
[00:34:24] Daniel: where was I that day?
[00:34:27] Jacinta: That explains a lot.
[00:34:28] Daniel: Yeah.
[00:34:28] Francois: It basically
[00:34:29] Daniel: made that ringing in my ears that day.
[00:34:32] Jacinta: 2022? I mean, we were probably still in lockdown at some or something like, or some sort of-
[00:34:38] Francois: Was that still lockdown?
[00:34:38] Jacinta: I mean, we were social distancing, I suppose. But anyway, a ringing in the atmosphere.
[00:34:44] Daniel: That’s, yeah that’s a good question. Back to the beginning of this episode when we were recording in here, when did we come back in here?
[00:34:50] Jacinta: when there was a long break of three years.
[00:34:53] Daniel: Where we just recorded online.
[00:34:54] Jacinta: Yeah. Because I got stuck in Australia for a year and a half.
[00:34:57] Daniel: Oh right.
[00:34:58] Jacinta: And we had to social distance before that, so.
[00:35:00] Daniel: Oh man. Yeah.
[00:35:00] Francois: You had to teach from Australia?
[00:35:02] Jacinta: I did, yeah.
[00:35:03] Francois: For a year?
[00:35:03] Jacinta: Yeah.
[00:35:03] Francois: That was my class.
[00:35:04] Jacinta: Yes. That was your class that I, that I lectured third year online from Australia. Which was not unusual at that point ’cause everyone had been learning online. But anyway. We digress significantly.
[00:35:14] Daniel: Sorry, that was my bad.
[00:35:15] Jacinta: But I think that, I think we’ve covered GRBs now.
[00:35:18] Francois: Yeah. Pretty decently.
[00:35:19] Jacinta: So why don’t we get back to what we used to do in here at the end of an episode, which is check in. How are you?
[00:35:23] Daniel: Oh yeah. Wow.
[00:35:24] Jacinta: Yeah. How are you Francois?
[00:35:26] Francois: I’m well, really busy with getting stuff ready for my thesis. I have something to write up at least now. Finished a little project, which I thought would take about two months and it took six, apparently that’s normal.
[00:35:44] Jacinta: That’s very normal yeah.
[00:35:46] Francois: Yeah and I’m making ready- I am getting ready to leave to Sutherland tomorrow. I have an observation run on the 1.9 meter telescope again, so looking forward to that.
[00:35:55] Jacinta: Cool.
[00:35:55] Francois: I actually quite like observing, yeah.
[00:35:56] Jacinta: Looking, well, I look forward to hearing about that when you come back next time.
[00:36:00] Daniel: Yeah I hope you get some good weather because it’s been absolutely diabolical. The trust me. I know. Actually, I think yesterday the wind didn’t get below 80 kilometers an hour.
[00:36:09] Jacinta: Gosh. Wow. And Sutherland of course where all the telescopes for the South African Astronomical Observatory are based. Dan, how are you?
[00:36:17] Daniel: I’m alright. It’s been a while since we’ve had a checkin, so I think a lot has happened, but, in general doing okay, thanks a lot going on as always. One of the things which is coming up which we can feature in an upcoming episode is the, it’s the 20th anniversary of SALT
[00:36:34] Jacinta: Yeah. Yes getting constructed.
[00:36:35] Daniel: So very busy with that, getting ready for some celebrations up in Sutherland again and yeah. Getting all the everything in, in a row for that and that’ll be very exciting.
[00:36:47] Jacinta: Yeah.
[00:36:48] Daniel and Francois: How are you, Jacinta?
[00:36:50] Daniel: Jinx.
[00:36:50] Francois: Jinx
[00:36:54] Jacinta: I’m well considering actually, I had a bit of a tumble down the stairs on the weekend and, have two bruised knees and a very bruised ankle. It’s about the size of a tennis ball.
[00:37:04] Daniel: How’s the ego?
[00:37:06] Jacinta: It’s humbled. Humble.
[00:37:08] Daniel: Also bruised.
[00:37:08] Jacinta: Yeah. Yes. Bruised, bruised, ego. That’s true but, I didn’t break anything, which is a miracle, so I’m very grateful for that. That is great and just appreciating how well most of my body works most of the time, at the moment. So, yeah. But, just moving slowly.
[00:37:24] Francois: That’s great.
[00:37:25] Jacinta: Very slow. I’m using an umbrella as a walking stick.
[00:37:29] Francois: Look a bit like Nanny McPhee, Mary Poppins, yes.
[00:37:34] Daniel: I’m just a spoon full of sugar.
[00:37:35] Jacinta: Yes so you saying-
[00:37:38] Daniel: That’s Jacinta singing.
[00:37:38] Jacinta: do I get to eat chocolate all day? That’s what I’m hearing.
[00:37:41] Daniel: Totally. Yeah.
[00:37:41] Jacinta: Fantastic, fantastic.
[00:37:43] Francois: Oh, I forgot to mention, I also just came back from my first ever conference overseas.
[00:37:48] Jacinta: Oh.
[00:37:48] Daniel: Oh, that’s incredible. Where’d you go?
[00:37:50] Francois: Hamburg, Germany.
[00:37:51] Daniel: Oh, nice.
[00:37:52] Jacinta: Tell us about it.
[00:37:53] Francois: That was great. It was actually, I met Simon there.
[00:37:55] Jacinta: Oh, cool.
[00:37:55] Francois: Come to think of it.
[00:37:56] Daniel: This really should’ve been mentioned earlier.
[00:37:58] Francois: Yeah, probably. Yeah I met Simon at that conference it was about the BlackGEM telescopes, which we will talk about in a future episode. But they are very, actually really, to do with what we were talking about ’cause they are designed to detect the optical counterparts to gravitational wave emissions.
[00:38:18] Jacinta: Oh, cool.
[00:38:18] Francois: Which we will probably discuss in the future episode.
[00:38:21] Jacinta: Well the time we’re on our camera’s about to go off. So we better wrap this up.
[00:38:27] Francois: Yes.
[00:38:27] Daniel: Should we do a final wave?
[00:38:31] Jacinta: Alright. So that’s it for today. Thank you very much for listening, and we hope you’ll join us again for the next episode of the Cosmic Savannah.
[00:38:38] Francois: You can visit our website, thecosmicsavannah.com, where we will have the transcript, links, pictures, and other stuff related to today’s episode.
[00:38:46] Daniel: You can follow us on X, Facebook and Instagram at Cosmic Savanna and now also on TikTok. I don’t even know what that is. That’s Savannah spelled S-A-V-A-N-N-A-H. You can also watch the podcast on YouTube with closed captions, which can be auto translated into many different languages, including Afrikaans, IsiXhosa and IsiZulu.
[00:39:04] Jacinta: Special thanks today to Dr. Simon De Wet for speaking with us.
[00:39:08] Francois: Thanks to our audio editor Nick Rushton, our podcast manager, me our social media manager Sumari Hattingh, our assistant manager, Kaashifa Saloojee and our other awesome interns.
[00:39:20] Daniel: Sisa Shibane, Karabo Rantwane, Kamohelo Letsoalo, Thato Nombewu and Charmaine Mputi.
[00:39:27] Jacinta: Thanks to today’s incredible videographers. From Visual Pill Productions, they are Rizwaanah Saloojee, Salvador Marcial and Reese Brice. Also thanks to Susie Cares for graphic design and Brian Masemola and Mija Wojcik for photography.
[00:39:43] Francois: We gratefully acknowledge support from the South African National Research Foundation, the Square Kilometer Array Observatory, the South African Agency for Science and Technology Advancement. The South African Astronomical Observatory, the University of Cape Town Astronomy Department, and the One Button Studio at UCT.
[00:39:59] Daniel: You can subscribe on Apple Podcast, Spotify, or wherever you get your podcast and we’d really appreciate it if you could rate and review us and recommend us to a friend.
[00:40:08] Jacinta: We’ll speak to you next time on the Cosmic Savannah.
[00:40:28] Daniel: When are you a doctor?
[00:40:31] Francois: No. No.
[00:40:32] Jacinta: Every episode can happen. Every episode.
[00:40:35] Francois: It takes a while.
[00:40:37] Jacinta: You haven’t started your PhD yet?
[00:40:39] Francois: No.
[00:40:39] Jacinta: You still masters?
[00:40:40] Francois: I’m stuck in Masters.
[00:40:41] Jacinta: You should say and not a master.
[00:40:44] Francois: Still not a master not even a doctor.
[00:40:47] Daniel: Just a, just a, just a bachelor.
[00:40:50] Francois: Yeah.
[00:40:51] Jacinta: Hello everyone.
[00:40:53] Francois: Hi, that’s, you know, we should probably look at the camera at some point, right when we say, we’ll do it in a minute when announce what we do.
