Podcaster: Jacinta Delhaize and Dr Daniel Cunnama; Guest: Prof Matthew Bailes
Title: The Cosmic Savannah – Ep. 66: Meertime Mysteries – Pulsars & Prizes
Link : www.thecosmicsavannah.com ; @cosmicsavannah (twitter, facebook & instagram); https://thecosmicsavannah.com/episode-66-meertime-mysteries-pulsars-and-prizes/
Description: Professor Matthew Bailes returns to discuss his recent work on Pulsars as well as his thoughts and feelings on winning the 2023 Shaw Prize for the discovery of Fast Radio Bursts.
Professor Bailes was awarded the 2023 Shaw Prize in Astronomy along with Duncan Lorimer & Maura McLaughlin for the discovery of Fast Radio Bursts. Congrats!
During the episode Professor Bailes discusses new and exciting insights from his recent research, his work on the Meertime project, how his spam filter nearly cost him the Shaw Prize and why microwaves must be used with caution when searching for Fast Radio Bursts.
Bio: Dr Jacinta Delhaize and Dr Daniel Cunnama are astronomers based in Cape Town, South Africa. Jacinta is a Research Fellow at the University of Cape Town. She spends her time using huge radio telescopes to study gas and black holes in distant galaxies.
Daniel is the Science Engagement Astronomer at the South African Astronomical Observatory. He likes to use large supercomputers to create simulations of galaxies. Both Jacinta and Daniel love to promote the incredible astronomy happening across the African continent.
Professor Matthew Bailes is an astrophysicist from the Centre for Astrophysics and Supercomputing at Swinburne University of Technology and the Director of OzGrav. His work primarily focuses on millisecond pulsars and detecting Fast Radio Bursts.
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Transcript
[00:00:00] Jacinta: Welcome to the Cosmic Savannah with Dr. Jacinta Delhaize
[00:00:08] Dan: and Dr. Daniel Cunnama. Each episode, we’ll be giving you a behind the scenes look at world class astronomy and astrophysics happening under African skies.
[00:00:16] Jacinta: 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] Dan: Sit back and relax as we take you on a safari through the skies.
[00:00:34] Jacinta: Hi, and welcome to today’s episode. Today we are talking with Professor Matthew Bailes from the Swinburne University of Technology about fast radio bursts, pulsars, and things like that.
[00:00:46] Dan: Yes, so we’ve spoken to Matthew Bales some time ago, one of our early episodes.
[00:00:51] Jacinta: And we actually just reran it as a, well, as a rerun of the previous episode.
[00:00:56] So if you haven’t had a listen to that one yet, or you haven’t heard it before, go and have a listen to that. And Matthew’s going to give us an update on his work with pulsars and the MeerKAT telescope and his MeerTime project.
[00:01:08] Dan: Yeah. So a couple of things have happened since we last spoke to Matthew.
[00:01:11] MeerKAT itself is really operating really well. And Matthew’s working on that with some exciting updates, which he’ll be able to share with us. He also was recently awarded the prestigious Shaw Prize, which we’ll talk to him a little bit about. That was for his and his colleagues’ discovery of fast radio bursts.
[00:01:29] Jacinta: Yeah. And the Shaw Prize, it’s kind of like the quote unquote, the Nobel Prize of the East, or I think it’s awarded by Hong Kong, right?
[00:01:37] Dan: Yeah. And, and then often a precursor, sort of like a nomination for a Nobel prize, although it does come with.
[00:01:45] Jacinta: Substantial monetary prize money.
[00:01:49] Dan: It’s like that lottery ticket that astronomers take, you know, or all scientists take.
[00:01:54] You know, we don’t get paid particularly well, we get to do what we like, and one day we might win the lottery.
[00:02:02] Jacinta: If you happen to make a sudden discovery of something.
[00:02:05] Dan: I’m not saying that Matthew won the lottery by discovering fast radio bursts, but I’m just saying that he did state that C1 and it was a fast radio.
[00:02:13] Jacinta: Okay, good. We’ll end it there.
[00:02:15] Dan: Okay.
[00:02:15] Jacinta: Well done. Okay. Well, okay. Well, so, so Matthew’s going to describe it all to us, but just very quickly, what’s a fast radio burst?
[00:02:22] Dan: So, that’s something which we don’t know and we can ask Matthew that question, but essentially it is, a burst of radio light that’s picked up by a radio telescope, which we don’t really know the origin for.
[00:02:33] We’ve now detected more and more of them, and we have some ideas, which Matthew will talk to us about, what they could possibly be coming from. But it’s a very, very bright burst of radio emission, which we’re picking up. So not, not one of the normal observations we’re making.
[00:02:47] Jacinta: Mm hmm. And that is something that we think is slightly different, though could be related, to a pulsar.
[00:02:52] And what is a pulsar?
[00:02:54] Dan: So a pulsar is a very fast spinning star, generally a neutron star, and that it’s a very very dense object, it’s spinning incredibly quickly, sometimes milliseconds or less, and it is beaming out radiation, radio light again, like a lighthouse. So every now and again it passes by us, the beam passes over us, and we get this pulse, hence the name ‘pulsar’.
[00:03:18] And we can monitor these things with our radio telescopes, we’ve discovered a lot of them. And they all kind of have their own unique fingerprint.
[00:03:26] Jacinta: And that is as opposed to a neutron star?
[00:03:29] Dan: So a neutron star could be a pulsar, as I said, but a neutron star is a very, very dense star, something, you know, the mass of our sun, uh, which is 700, 000 kilometers across, but compressed into a very small star about 12 kilometers across. So the atoms, the hydrogen or helium within the star have collapsed, and they’ve lost their electrons. And now you have this very, very dense core of neutrons only, which make this very dense star.
[00:03:58] Jacinta: So 12 kilometers, that’s what the distance between Cape Town and
[00:04:02] Dan: Observatory, where we’re sitting at the moment.
[00:04:05] So it’s like, you know, it’s like the, the CBD of a, of a city. It’s really not a long distance.
[00:04:10] Jacinta: Okay. There you go. So that is what a neutron star is. And of course it’s, it’s produced in a supernova explosion, right? When massive stars die at the end of their lives, they can explode. And what can remain at the end of that is, is some sort of what we call an exotic object, which could be a neutron star, where essentially all of your protons and your electrons have compacted together and ended up just forming, pure neutrons, which is the densest object in the universe. Well, except for one, which is a black hole, where of course it’s so dense that not even light can escape and we can’t see it. So we call it a black hole. So those are the two possible end points of a massive supernova explosion.
[00:04:49] Dan: Correct.
[00:04:50] Jacinta: Yes. And, uh, I know my stellar evolution.
[00:04:54] And so of course, as Dan said, if your neutron star has a strong magnetic field and it’s rotating, then that’s what we might be able to see as a pulsar. And they’re really useful for tracking a whole bunch of things in the universe. They are useful for trying to figure out what kind of intergalactic medium or interstellar medium is between us and the pulsar.
[00:05:12] So like gas and dust and stuff like that, trying to figure out, it doesn’t really glow very much. So this is one way to try and probe or study that kind of matter in between. And also on the larger scales, timing or studying gravitational waves as well.
[00:05:27] Dan: So hopefully that’s given you a nice little overview of what we’re going to be talking about today.
[00:05:31] If you didn’t listen to the last episode with the with a rerun, then maybe some of the topics we’ll be talking about today might get a little bit technical. Matthew does get a little bit technical at times, but it’s a very interesting interview. And he, you know, he, he shares some wonderful anecdotes. So, so bear with us through some of the technical stuff, if that isn’t your area of expertise or interest.
[00:05:51] Jacinta: Don’t worry, I didn’t understand everything either. So just, but just power on through that.
[00:05:56] Dan: Uh, yeah. And we, we hope you enjoy the episode.
[00:05:58] Jacinta: Let’s hear it from Matthew.
[00:06:07] With us now is Professor Matthew Bales, who is a professor at the Centre for Astrophysics and Supercomputing at Swinburne University of Technology, and also the Director of the ARC Centre of Excellence for Gravitational Wave Discovery. Welcome to the Cosmic Savannah, Matthew.
[00:06:25] Matthew: Yeah, thanks very much Jacinta and Dan, it’s a pleasure to be here back here in South Africa.
[00:06:29] Dan: Yeah, pleasure to have you back on the podcast. We had you some years ago, back in 2019. And we replayed that episode just this last week.
[00:06:36] Jacinta: Yeah, it was episode 29.
[00:06:38] Matthew: All right.
[00:06:39] Dan: Now we’re over 60, I think.
[00:06:41] Jacinta: Yeah, I think we’re up to 65 now or something.
[00:06:43] Dan: But enough about us. Yeah, welcome back to the podcast.
[00:06:48] And since we last chatted, there’s been quite a few developments in your field of pulsars and FRBs. And thanks for joining us today to talk about them.
[00:06:57] Jacinta: Yeah. How have you been?
[00:06:59] Matthew: Oh, it’s good to be out the other side of the pandemic. I’ve really missed people. And, um, I’ve loved being back in the office and actually talking to people and relating to people and seeing their smiling faces and helping them with their work and it’s just been good to be re-energized by that human interaction.
[00:07:18] Jacinta: Yeah, and international travel as well, you’re able to come back to South africa.
[00:07:21] Matthew: Yeah, I haven’t missed the time on the aeroplane, but it is nice to be back visiting old friends.
[00:07:27] Dan: So your trip to South Africa this time, what are you visiting us for?
[00:07:31] Matthew: Yeah, a couple of things. We like to be able to get the South African next generation involved in pulsar and fast radio burst research.
[00:07:41] You’ve got such a wonderful telescope here that’s really at the forefront of radio astronomy. It’s situated in the best hemisphere to study neutron stars, the majority of which are in the southern skies. And the MeerKAT telescope has such an amazing collecting area and performance that it’s really excelling at monitoring neutron stars.
[00:08:03] So, we want to develop the next generation of African scientists to, to help lead this area especially with the coming of the SKA in a few years time.
[00:08:13] Dan: Great. So we’d really like to get into the, the pulsars and the, the new group which is sort of forming here and MeerTime and how we, you know, how we’re contributing to the pulsar discoveries.
[00:08:23] But before we go on to that, I just wanted to raise one other thing, which is that you were recently awarded the 2023 Shaw Prize. So a huge congratulations from us. And this was for the discovery of fast radio bursts, which we have discussed before. So yeah, congratulations. And maybe you can just give us a little overview of of how that discovery was made, what it means to have won the Shaw Prize.
[00:08:50] And the rumor is that the Shaw Prize kind of leads to the Nobel Prize at some point. I’m not saying, I’m just saying,
[00:08:59] Jacinta: Well, the Nobel Prize in physics for this year was awarded yesterday. It was announced yesterday and it didn’t go to astronomy. It did go to, uh, it did go to, um, what was it, Attosecond science and the fifth woman ever to win the Nobel Prize.
[00:09:13] It was split between three and one of them was a woman. Yes. Uh, but anyway, back to you, Matthew. So yeah, congratulations on the prize and maybe you can start by just telling us what FRBs are, fast radio bursts.
[00:09:23] Matthew: Yeah. The prize was co-awarded, if you like, to myself, Duncan Lorimer and Maura McLaughlin.
[00:09:30] They’re both professors of astronomy at West Virginia University. And many years ago, Maura developed a new technique of looking at the sky for bursts of radio emission. And, uh, up until that time. We were mainly interested in the high time resolution universe in order to discover radio pulsars, which are regularly pulsing bursts of radio waves, thought to arise from a sort of rotating lighthouse beam of radio waves that sweeps past your telescope once a rotation.
[00:10:03] And people have developed great techniques for finding these regularly repeating bursts of radio waves and and Maura was the first person to use the Parkes telescope to do a very comprehensive survey of the galactic plane and she discovered I think it was around a dozen new sources that were just one off flashes of radio waves and when she followed them up, she found that actually if you looked at them long enough, they would repeat. So there was this sort of flurry of activity to discover more of these one off radio bursts and her husband Duncan was supervising a summer student, um, called David at the time, but now likes to be called Ash, and she was looking through the survey data from a nearby galaxy, and saw this remarkable flash of light.
[00:10:57] I was very fortunate that I was at the… Parkes radio telescope with Duncan who coincidentally was my first ever student and I just asked him if he’d found anything interesting lately And he said, “hm”, he said “Have you ever seen anything, um in your data that was so bright that you saw it in more of more than one beam of the Parkes 13 beam receiver?”
[00:11:19] And I said, “Yeah, I, I, I have. Um, not very often, but, you know, it was a pretty bright millisecond pulsar we discovered not so long ago that also showed up in more than one beam. And so that was interesting. So we sort of downloaded the data and looked at what’s called the dynamic spectrum. This is the power as a function of both frequency and time.
[00:11:40] And there was just this amazing swept radio signal consistent with something coming from a very long way away, and we were a bit staggered to find out that instead of being in the nearby galaxy, it was actually about a billion light years away and had a trillion times the luminosity of any similar pulse that we’d ever seen in our galaxy.
[00:12:02] And I was like, “Oh!”
[00:12:05] Jacinta: My God! Okay, so definitely not in the Milky Way, really, really far away, right?
[00:12:08] Dan: It’s nice when we have these discoveries that are actually… Oh my god.
[00:12:11] Jacinta: Yeah. You just have a moment.
[00:12:14] Matthew: Yeah. No, I still remember looking at the plot and Duncan was next to me and Duncan’s this lovely fellow and he’s very understated and he just started laughing.
[00:12:24] He sort of chuckled because he, he was so struck by, by how bright the thing looked. And then we sort of downloaded various bits of data overnight and processed it and realized that the radio frequency interference automatic routine had actually deleted it in one of the 13 pixels. And when we turned off the radio interference remover, there was this amazing stripe which had saturated the receiver and caused so much damage to the 1 bit digitizers algorithm that it had concluded it must be interference, so it was almost deleted.
[00:13:04] Jacinta: So it was an automated algorithm that almost deleted the main event. Somewhat like your announcement of your Shaw Prize.
[00:13:11] Dan: Yes, go into that.
[00:13:13] Matthew: Yeah, look, I was in a bit of a grumpy mood and, you know, I had a lot of admin to do and I was just sitting at my desk on my computer going through lots of administrative tasks as we somehow seem to get caught up in these days as senior managers and there was a little boop on my, my screen. And it was a, a text message on Google chat from Duncan saying, “We just won the Shaw prize.”, full stop. And I wondered if it was some sort of spam bot or joke or whatever. And I thought, well, nobody’s told me, I thought this can’t be right. And I said, “Who won the Shaw prize?” And he said, you, me and Maura. Check your email. So I looked at my email. There was nothing there. I thought is it in spam and I went to spam and it’s congratulations, you’ve won one third of some large amount of money. Click here for more details I’m not clicking this link
[00:14:14] Jacinta: Oh my god
[00:14:14] Dan: So you did click the link?
[00:14:16] Matthew: Yeah, I did.
[00:14:17] Dan: And they did give you the money?
[00:14:18] Matthew: Well, I marked it as not spam.
[00:14:21] Dan: I need to go through my spam folder.
[00:14:23] Jacinta: Yeah, right? Just in case there’s a massive monetary prize there. Alright, so you found this, uh, you found this signal of this crazy bright object that’s far away.
[00:14:33] Do we know what it is yet? Do we actually know what causes it?
[00:14:36] Matthew: We do know that in our own galaxy there is a source. of fast radio bursts known as a magnetar. But that doesn’t mean everything is a magnetar that gives off a fast radio burst. So there could be other things in the universe that are capable of giving off fast radio bursts.
[00:14:55] Maybe they have the right combination of magnetic field and rotation or something. It’s almost certainly some sort of compact object. It’s probably a neutron star. The time scales involved in the fast radio burst emission are very, very tiny. So they can be just a few microseconds in duration. So whatever’s creating it probably isn’t much bigger than a few microseconds times the speed of light.
[00:15:23] And that’s consistent with something in the magnetosphere of a very magnetic neutron star. It’s about as much energy. In the Lorimer Burst as the sun gives off in a month, which sounds like a lot, but something like a rotating neutron star with a magnetic field, that’s about what a normal pulsar has would be able to give off one of these things every few seconds without violating laws of conservation of energy.
[00:15:55] And that’s partly because radio waves are such an efficient way of transferring information across the universe, and luckily sometimes to the Parkes Telescope.
[00:16:04] Dan: And if it is a magnetar, why is it a one off event? I mean, so we know pulsars are from, you know, rotating neutron stars like you mentioned, like a lighthouse sweeping over us.
[00:16:13] Is that just because of the orientation or is there something else going on?
[00:16:18] Matthew: Yeah, the um, the first fast radio burst discovered, not at the Parkes Telescope, was actually found at Arecibo, the giant 305 metre dish by Laura Spittler. And because it was the only one they had, they were doing a follow up campaign. And they discovered that this particular fast radio burst source did repeat. And so being imaginative people, we called them repeaters. So there are a class of fast radio bursts that repeat. They tend to have different time characteristics than what we call the one off fast radio bursts.
[00:16:59] It wouldn’t surprise me if they have a similar origin, but maybe there’s something about the environment of a repeating FRB that triggers fast radio bursts more often. Some of the repeating fast radio bursts seem to have seasons where they’ll repeat very often and then they’ll go away for a few months or and then they come back and somebody or a couple of groups have shown that there’s two that have almost like a periodicity of between a few months and six months or so.
[00:17:34] Where there’s a season, you know, roughly half the time that you can see repeats and there’s a season when you can’t. So there is a thought that maybe this is related to an orbit, of a neutron star around another star, or maybe there’s some precession cycle where at some angles it points at you and at some it doesn’t.
[00:17:58] Um, but it, it’s one of the great, sort of active areas of fast radio bursts. We’re sort of in two minds as to why to study them. One is to try and understand what’s causing them, and then the other is to use them as a tool in which to study the universe.
[00:18:13] Jacinta: And when you say season, you don’t obviously mean the Earth’s season, like summer or spring or anything, right?
[00:18:18] It’s, it’s like a patch of time related to the object itself, right?
[00:18:22] Matthew: Yeah, and it might be, like, in the same way that the Earth’s seasons are related to how long it takes us to go around the sun. Maybe the repeating FRB seasons are related to how long they take to go around their host star, or it might just be coincidental that it’s very similar orbital periods to neutron stars going around massive stars, which is usually somewhere between a few weeks and a few years.
[00:18:46] So it might be coincidental, but it might have nothing to do with orbits at all, which is kind of interesting.
[00:18:53] Jacinta: And you mentioned a Lorimer Burst. What’s, what’s that? Is that the same as an FRB?
[00:18:57] Matthew: Yeah, so the first paper to announce of a fast radio burst was led by Duncan Lorimer. And then I noticed at some point that we were going to conferences and people were talking about the Lorimer Burst.
[00:19:09] And I thought, well, that’s pretty cute. Um, it’s nice to have your first student have something named after them.
[00:19:15] Jacinta: Oh, Duncan Lorimer was your student?
[00:19:17] Matthew: Yeah, he did a master’s with me at Jodrell Bank.
[00:19:20] Dan: And she had the short breath.
[00:19:22] Jacinta: Oh, well, I know that part.
[00:19:24] Dan: Keep up.
[00:19:25] Jacinta: Sorry. Sorry.
[00:19:26] Matthew: Then we had a sort of an era of controversy where although the Lorimer Burst was ridiculously bright, nobody with any telescope could find another one for about five years.
[00:19:38] So there was a, a sort of moment of reflection and sort of, is this actually real? Maybe it’s interference?
[00:19:46] Jacinta: Is it a microwave being opened?
[00:19:49] Matthew: Yeah, I had a student, Sarah Burke Spillore, that I remember she excitedly you know, sent me an email saying, I just found another Lorimer Burst. I went, “Yes, this is awesome!”
[00:20:00] And then she said, but unlike the Lorimer Bursts, instead of in three beams, it’s in all 13. And I thought, “Oh dear”, because you can only be in present in all 13 beams, if you’re in what we call the near-field, which is a zone around the telescope where the radio waves light up all the receivers, you have to be at parks within a few kilometers to be in the near-field. I was like, “Oh my God, there’s something giving off Lorimer bursts in the vicinity of the telescope.” And it actually took many years to track it down. It was a, another student and an army of postdocs and. that eventually discovered that every time you open the microwave oven at the Parkes Observatory, it gave off something with somewhat similar characteristics to the Lorimer Burst but it never looked actually quite as perfect and it was sort of blotchy. So the true believers still believed in the Lorimer Bursts, but I must admit I was having grave doubts.
[00:20:57] Jacinta: Oh, so you were doubting the existence of Lorimer Bursts at all at that point?
[00:21:02] Matthew: Well, like some people. are naturally overconfident and others are full of self-doubt and I think I’m in the latter category which might seem a bit ironic for a Shaw Prize winner but, um, skepticism.
[00:21:16] I was a bit, a bit worried that it may not be real and that we might have been fooling ourselves. And then, fortunately, a bunch of us had decided to r- engineer the Parkes telescope with more of a digital, what we call, back-end to the telescope, which was much more sensitive to Lorimer-like Bursts. And one of the students at Manchester, Dan Thornton, found another four in a big survey that a big group of us were doing. And that was a great relief to see them. And a year earlier, a guy called Evan Keen had… I found what looked a bit like a Lorimer Burst in one of the Park’s old surveys. The only problem was it was right in the galactic plane, and it was a little bit unclear whether it was really just in our galaxy or far beyond it.
[00:22:09] I honestly believe that it probably was far beyond it, but it just, you couldn’t, it wasn’t completely unambiguous.
[00:22:15] Jacinta: Yeah, distances are really hard to measure in astronomy, notoriously hard.
[00:22:20] Dan: So you talk a lot about FRBs and, and, you know, how they’ve been discovered. With the advent of all these new telescopes, and you mentioned MeerKAT already, what’s next for FRBs?
[00:22:29] Are we, are we getting closer to a better understanding of them? Are we getting more and more detections of them?
[00:22:35] Matthew: Yeah, so each FRB used to be like a nature paper once upon a time. There’s now over 700 that have been published. There’s a remarkable telescope in Canada called Chime, which was actually designed to do neutral hydrogen cosmology, but it got re-engineered by a team led by Vicki Kaspi who’s a professor at McGill, and also a Shaw Prize winner a couple of years before us.
[00:23:01] Um. Mm. Mm. And they managed to turn that machine into something that finds about three fast radio bursts a day. They’ve only released a few hundred, or maybe seven hundred of them, I think it is, to date. But that thing’s really finding all sorts of repeating FRBs and strange FRBs, one that seems to be coming from a globular cluster, and it’s been helping to transform the field.
[00:23:29] On the other hand, there’s other instruments that are designed to localize them. So, although CHIME finds a lot of fast radio bursts, it’s only if they repeat that they can actually localize them to the host galaxy. There’s other telescopes like ASCAP in Australia, there’s a new one called DSA 110 in California, and of course, MeerKAT, that are very good at localizing them
[00:23:52] And that’s letting us work out… Which galaxies fast radio bursts come from, but what’s really interesting is if you’ve got a redshift to the galaxy, you can actually count the number of electrons in the universe and that’s a phenomenal application of fast radio bursts and I think why they’re they’re so interesting so you can effectively count the number of electrons by noticing what is the delay between the high frequency radio waves and the low frequency radio waves?
[00:24:22] And that tells you how many electrons there are between us and the source and that’s very interesting for cosmologists.
[00:24:28] Dan: So how many electrons are there?
[00:24:33] Matthew: It’s about one per cubic meter in the universe. Okay, that’s not a lot.
[00:24:39] Jacinta: Is that a lot or not a lot? That’s not a lot. Is it not?
[00:24:42] Matthew: It’s enough to cause… A delay of, of typically a few hundred milliseconds
[00:24:48] I’m glad it’s not too much more than that, or we would not be able to, uh, search for the fast radio bursts as efficiently.
[00:24:55] Dan: So this has implications for like this. scale of the universe for some of our standard candles.
[00:25:01] Matthew: Yeah, it’s not so much the, the scale, it’s more the density of the universe. Um, how much what we call baryonic matter, like the stuff you and I are made of, we can work out how much of that is, is present.
[00:25:14] And there was a famous problem in cosmology called the missing baryons. And these were atoms that were difficult to identify the presence of, because normal light doesn’t actually get affected very much by by electrons in the, in the galaxy, light just sort of goes straight past them. Fortunately, radio waves get this delay, and they give us this handle on how many electrons are in the universe.
[00:25:39] And most of the material in the universe is actually not in galaxies, it’s just floating around between them. So this is a really great way of doing a, a galactic census of the number of electrons and hence protons in the universe.
[00:25:52] Jacinta: So we can study the intergalactic medium, is that right?
[00:25:55] Matthew: Yeah, it’s a missing matter detector in some sense, although it’s not the missing matter, which doesn’t appear to be.
[00:26:04] Jacinta: So it’s not dark matter?
[00:26:05] Matthew: No, there’s too many matters, but I’m quite proud to be associated with what I call real matter, and other people can do the fantasy stuff.
[00:26:14] Jacinta: All right. Okay. So my, my, one of my research fields is galaxy evolution and AGN, active galactic nuclei, which are supermassive black holes in the centers of galaxies that are feeding and growing.
[00:26:25] So can fast radio bursts have anything to do with that or is it really not related to these black holes and more related to kind of individual stars, do you think?
[00:26:34] Matthew: Look, there’s so much energy that is generated when you fall into a black hole. You only need a tiny amount to come out in the radio to create a, a fast radio burst.
[00:26:46] Whether or not something orbiting a supermassive black hole has the right time scale to give rise to a sort of few hundred microsecond burst, I think that’s probably pretty improbable. But maybe a neutron star or a black hole that’s in the presence of a, a giant star that’s feeding it material. There might be something in the accretion disk of those that…
[00:27:09] It might be sparking, or it might be that something like material being accreted onto a very magnetic neutron star sort of sparks something in the magnetosphere that gives rise to a fast radio burst. I’d love supermassive black holes to be involved somehow, but there’s other ways to study them.
[00:27:31] Jacinta: Yes, there are, even with radio telescopes.
[00:27:34] Dan: Yeah, so we’ve talked a lot about FRBs but we’d also like to chat to you about pulsars. You know, recently there’s been some discoveries related to pulsars, notably the discovery of the sort of low pitched hum of gravitational waves seems to be pervasive in the universe. And you mentioned, you know, you’re working with MeerKAT and the MeerTime project.
[00:27:56] Can you give us a little background about what Meertime’s doing and what work you’re doing with the pulsars using MeerKAT?
[00:28:03] Matthew: Yeah that would be great. The radio pulsars that I personally love to study are ones called millisecond pulsars. These are neutron stars that rotate anywhere between 700 times a second and maybe 100 times a second.
[00:28:18] They’re thought to be once normal neutron stars, just born in a supernova explosion, that have accreted matter from a companion and had an accretion disk form around them, which not only seems to destroy the magnetic field, but also make the neutron star spin up very, very quickly. The speed of a rotation disk near a neutron star surface is near the speed of light and this makes it spin up to these millisecond periods.
[00:28:49] Fortunately a little bit of magnetic field is left alive and enough to power a radio beam and I spent my early years in astronomy searching for millisecond pulsars, and now I do what’s called timing them. The pulse as it sweeps past the radio telescope is a little bit random, but there’s so many thousand pulses coming at you every few seconds that the average pulse actually is a very stable quantity.
[00:29:17] And you can… Look at that average pulse and ask, when would it have hit my telescope? And you can do something we call pulsar timing, where you literally count every rotation of the neutron star And so any change in the path length between us and the pulsar gets recorded as a time delay.
[00:29:37] And because of this, we can study how neutron stars spin, whether they have star quakes or not. If they’re orbiting another star, we can measure that orbit to astounding precision. We can see the orbit shrinking,
[00:29:50] But most excitingly, If there’s supermassive black holes in the universe, they will be perturbing the effective distance between us and the neutron star and leading to a time delay which is potentially measurable.
[00:30:02] Jacinta: I’m sorry, you just said starquakes? What’s that?
[00:30:05] Dan: Is there a movie called that?
[00:30:06] Jacinta: I don’t know, but there should be.
[00:30:09] Matthew: Yeah, so we think that the magnetic field of a neutron star is anchored in the super fluid of the neutron star. So neutron stars actually have a fluid core, which we call a super fluid. It’s actually a superconductor, so it has no friction and it sort of spins forever. It’s also very good at transmitting currents, so it can anchor a magnetic field of a, a very high value, much higher than we can create here on earth.
[00:30:38] And if you spin a neutron star, there’s actually a torque exerted by the magnetic field as it rotates. Magnetic fields don’t like to rotate, they actually sort of protest. and that can occasionally cause the superconducting currents to snap, and that gives rise to what’s called a starquake.
[00:30:59] Instead of a starquake, it might be… thought of as a magnetic field quake and that gives rise to it a change in when the pulses arrive at the telescope and so if you look at a very young neutron star maybe once every few months to once every few years They have these star quakes and you can think of it If you had a an egg if you rotate an egg on a table The fluid actually rotates with the shell if you temporarily stop the shell, the fluid inside keeps spinning, and if you take your hand off the, the egg, it spins back up.
[00:31:35] Dan: Try this at home, kids.
[00:31:36] Matthew: And neutron stars do exactly the same thing. They have this crust of material around the neutron star, and they’ve got a superfluid inside it. And when they have one of these starquakes, you can actually see by counting the pulses and when they arrive at our telescope.
[00:31:51] Dan: Rad.
[00:31:53] Okay, star quakes aside, I mean, the other thing, which is a little bit like crazy and mind blowing is, so you’ve got all of these millisecond pulsars, which are essentially lighthouses out in space. And by looking at some correlation. Between the times that they’re reaching you, you’re measuring gravitational waves passing through the universe.
[00:32:15] So, now that the sort of background gravitational wave hum has been discovered, what are we going to learn from this array of pulsars that we’re observing with these new telescopes?
[00:32:27] Matthew: Yeah, so what we try and do is see if the arrival times of pulsars from different directions on the sky are correlated or don’t know anything about each other.
[00:32:39] If they don’t know anything about each other, um, they’re probably not… Experiencing the same delays. Fortunately, the Earth is the common thing, so we’re using telescopes on Earth to look at our neutron stars. And if the Earth is in a, a sort of a deeper potential well, if you like, or, or not, there should be correlations in the arrival times between pairs of pulsars that are near each other in the sky compared to ones that are, say, 90 degrees apart.
[00:33:08] Jacinta: So, and when you say correlations, you mean some sort of relationship between them?
[00:33:12] Matthew: Yes, the, the arrival time should arrive early in the same direction or late, um, between pulsars that are near each other on the sky. And if they’re a long way apart, there shouldn’t be a correlation between the arrival time.
[00:33:29] So if you look at… how correlated the signals are as a function of their separation on the sky. which should, um, demonstrate that the Earth is awash with, with gravitational waves.
[00:33:41] Jacinta: Okay, so… If two pulsars are really far away from each other, then they shouldn’t be experiencing any similar physical anything happening to their effects.
[00:33:53] And so the change in the arrival time of their pulses shouldn’t be related in any way, but we’re actually seeing that they are related. Is that correct?
[00:34:00] Matthew: That’s what we would. describe as tantalizing evidence.
[00:34:03] Jacinta: Tantalizing evidence. Okay. Very politically, politically correct answer there. All right. So there’s tantalizing evidence that there is some relationship between the arrival times.
[00:34:13] And then that is what is leading us to think that there’s some gravitational wave background. Is that right?
[00:34:19] Matthew: Well, galaxies at their cores have supermassive black holes in them. And if galaxies merge, eventually you would like to think the black holes will merge. When they do, they send out a burst of gravitational waves.
[00:34:33] We’ve seen these with what we call solar mass black holes with the LIGO gravitational wave detector. The galaxy full of pulsars is a bit like a supermassive black hole detector. But we’re unlikely to be lucky enough to see two black holes merge in the course of… days or weeks, but we might see them passing each other over the course of years and what we call the stochastic background, which is the sum of all of the black holes in the universe are all sort of making the earth wobble around a bit compared to the pulsars.
[00:35:07] And that’s what the, what we call pulsar timing arrays have published evidence of. So they’ve got. What we call a highly probable correlation somewhere between three and four sigma, which means that it’s kind of like 99 point something percent likely to be true, but it’s not completely unambiguous because other things cause correlations like a clock error at your telescope or an incorrect model of the, what’s called the planetary ephemeris, where all the planets are actually affects our arrival times, what the mass of Jupiter is important. And so it’s very important to show that the correlation is what we call quadrupolar as opposed to dipolar.
[00:35:53] Jacinta: Okay. Quadrupolar.
[00:35:55] Matthew: So when gravitation, when to supermassive black holes are near each other they cause a wave to travel out that stretches and squeezes space time. So, in the X direction it might be squeezing, but in the Y direction it might be pulling. And then, half an orbital period later, it’s the other way around. So you get this wave travelling throughout the universe. And that’s what gives rise to these… angular correlations between the pairs of pulsars. So,
[00:36:27] Jacinta: okay. So then we see like kind of stretching and squeezing of gravitational waves as they pass. And we’re detecting that through these pulsars, right? And how they changing.
[00:36:37] Dan: Can I try out an analogy on you? Tell me if I’m, tell me if I’m completely wrong.
[00:36:42] Okay. We’re standing on the beach. You’re looking at the waves. You said there’s the big waves. Coming in and they’re coming in fairly regularly and these are from let’s say, you know a large gravitational wave to emerging neutron stars or black holes something that LIGO can detect. This is a big wave what we’re looking at now is all these little ripples and waves which are going in all different directions
[00:37:06] Jacinta: Oh like the little ripples on the surface,
[00:37:07] Dan: You know, when you look at the sea and it’s like There’s just millions of little waves going in all different directions.
[00:37:14] Is that kind of what we’re looking at if we’re looking at the stochastic background?
[00:37:18] Matthew: Yes. It’s like what we call the superposition or the sum of so many little waves that we’re being buffered around in quasi-random directions, but they start, they still are spatially correlated because the Earth, is the common thing.
[00:37:34] Jacinta: Okay. So, so what caused all the little tiny ripples?
[00:37:37] Matthew: So little tiny ripples are probably just made from supermassive black holes that are so far apart that they will complete less than one orbit in a human lifetime. And there’s so many of them compared to the ones that are just in the midst of merging that they will usually dominate.
[00:37:56] If we get really lucky, we might have a pair of supermassive black holes somewhere in the universe that just merged while we turned our telescope on, but that’s fairly unlikely.
[00:38:07] Dan: So in back to my analogy Ultimately if we’re audacious astronomers Are we saying that if somebody throws a rock into the sea we’ll be able to know like we’ll be able to work out the source waves for each of these supermassive black holes and try and map that out based on the
[00:38:29] Matthew: Yeah, we’ll never be in a situation where we can describe the makeup of I’ll try that again.
[00:38:38] We’ll never be in a situation where we can identify the individual sources of the stochastic background, but we can say they have a certain spectrum, and we have good evidence of that from all of the pulsar timing arrays. Unfortunately, the pulsars themselves are not perfect clocks.
[00:38:56] They do things that help contaminate the signal and make it harder to find. So, the more pulsars you have… And the more accurately you can measure their arrival times, the more impact you can have in this field.
[00:39:09] Jacinta: The things that they do, is it starquakes?
[00:39:13] Dan: We do bigger things, bigger things.
[00:39:15] Jacinta: Okay, sorry.
[00:39:16] Matthew: The millisecond pulsars very rarely starquake, but they do do… strange things occasionally where they change their magnetic field geometry and their shape of their pulse changes. That’s annoying, but it’s not fatal.
[00:39:32] Jacinta: The universe is annoying.
[00:39:34] Dan: Sure is sometimes.
[00:39:36] Jacinta: Um, okay. So, so there’s this background of gravitational waves and tantalizing evidence has been found that it exists through pulsar timing.
[00:39:43] And that was announced in all over the news recently by a team called NANOGrav which I think is based in the US. Were you involved in that at all?
[00:39:52] Matthew: Yes, there are actually four announcements at the same time. NANOGrav probably have the most statistically significant detection, although there’s many different ways you can measure the significance of these detections, and the European pulsar timing array had a very similar statistical significance.
[00:40:13] Jacinta: So when you say statistical significance, you kind of mean like the strongest signal, right? Or the most reliable signal.
[00:40:18] Matthew: Or the one that’s most likely not to be a fluke. Okay, that’s a good way of saying it. Um, so the Americans had the giant Arecibo telescope, which was a very good pulsar telescope.
[00:40:29] Unfortunately, it It collapsed, and is no longer with us. They also have something called the Green Bank Telescope, which is a great pulsar instrument. The Europeans have about five or six telescopes that work in unison. And in Australia we have the old Parkes Telescope,
[00:40:46] Dan: Sorry, a single dish. Radiotelescope’s better for pulsars.
[00:40:51] Matthew: They’re certainly easier to find pulsars with, but there are some very interesting characteristics of interferometers that make their calibration more precise.
[00:41:01] MeerKAT was one of the first interferometers to be what I would call completely digital.
[00:41:07] So I think MeerKAT can have a great contribution to this field going forward and we were allocated over a thousand hours to look at millisecond pulsars all over the sky and we’ve been doing that roughly every two weeks since about 2019.
[00:41:23] Dan: I think firstly, just a basic, what is an interferometer? So that’s an array of radio telescopes working together essentially as one. And now you’re looking across the entire sky or a large portion of the sky.
[00:41:37] When you say you have a thousand hours, does that mean you’re observing constantly or every two weeks you just, have a look quickly or you know, how does that work because presumably these are these are pulses with pulses from pulsars which you want to be monitoring constantly
[00:41:53] Matthew: Yeah, so about every two weeks we get the MeerKAT telescope for between about 12 and 18 hours.
[00:41:59] And we run through a list of almost 90 millisecond pulsars. The very bright ones we don’t observe for very long, because we get a very good, what we call arrival time very quickly. Some of the fainter ones we dwell on for a little bit longer. And that gives us the maximum number of pairs of pulsars, which is what’s important for this gravitational wave detection.
[00:42:21] Jacinta: Okay, so you are the PI of a project on MeerKAT called MeerTime. So, um, you’ve already said a little bit about this, but can you tell us a bit more about MeerTime and what you hope to do with it?
[00:42:32] Matthew: Yeah, MeerTime actually got over 5, 000 hours of, of telescope time split between four themes. And one of the themes looks at millisecond pulsars in the cores of globular clusters.
[00:42:46] Another looks at… Neutron stars that are going around each other so fast that they display all sorts of relativistic phenomenon like light bending and what we call time dilation and gravitational wave emission. There’s the thousand pulsar array which is just monitoring a thousand pulsars that are quite slow but trying to understand why they emit radio waves the way they do. And then there’s the pulsar timing array, which is doing this search for supermassive black holes and how they perturb the arrival times of the pulses.
[00:43:20] Dan: And have you got any tantalizing hints yet?
[00:43:27] Matthew: I’m really stunned by the quality of the data and we’ve already, shown how accurately we can measure the arrival times and so if the background is, is present certainly within a year or so, we’ll be a world leader in the detection significance. We’re not yet at a point where we want to go public with, um, with what we’re seeing.
[00:43:54] Jacinta: Come on, we can get the scoop. No one’s listening.
[00:43:59] Matthew: Well, I think. Extraordinary claims require extraordinary evidence.
[00:44:03] Jacinta: Okay, I love that hint. I love that hint. Okay, so MeerKAT… it’s tantalizing. I’m tantalized.
[00:44:11] Dan: Okay, so, right, so some great stuff coming out of MeerKAT already and exciting stuff. But then beyond MeerKAT already, the SKA Observatory is on its way.
[00:44:23] I presume you’ll also be involved in that and its capabilities will be even better.
[00:44:28] Matthew: I’m involved in the construction and planning and lobbying for the SKA, but I actually intend to hand over the leadership of any projects to the next generation by the time it’s taking data.
[00:44:41] Dan: Very nice.
[00:44:41] Jacinta: Good, and I hope a large fraction of that is for the South African next generation, which will be awesome as well.
[00:44:47] Dan: Before we let you go, I have one last question. If you win the Nobel Prize, will you still talk to us?
[00:44:53] Matthew: You’ll be at the very top of my list.
[00:44:54] Jacinta: We heard that here first. We have that recorded.
[00:44:59] Matthew: But I’m um, I think there’s some things that are very obviously will win the Nobel Prize, and I don’t think fast radio bursts are in that category, but I didn’t think that about the Shaw Prize, so maybe I’m not very good. person to, to judge.
[00:45:12] Dan: Who knows what the Swedes think. Yeah.
[00:45:16] Jacinta: Hi Sweden if anyone’s from Sweden, hello. It’s the Swedish Royal Academy. Oh, that’s true. Okay. Um, well thank you very much for spending so much time with us today, Matthew. We know you’re a very busy person and we really appreciate it. Uh, we’ll let you go now and yeah, we hope to speak to you again when you come and visit us again.
[00:45:32] Matthew: That’d be great. Thanks very much.
[00:45:33] Dan: Thank you, Matthew. Take care.
[00:45:41] Jacinta: I loved your wave analogy, Dan. I’m not sure it works, but I loved the effort.
[00:45:45] Dan: Oh, thank you. I do love an analogy. I mean, it helps me to understand things. And I know, you know, it’s, it’s perhaps not the perfect analogy, but I have to have some sort of picture in my head. Otherwise, I can’t, I really can’t get my head around some of these topics.
[00:45:58] Jacinta: I know. And some of them are… so complex and abstract that you almost can’t have a picture in your head. And so you have to kind of like approximate dramatically.
[00:46:07] Dan: And I mean, the waves, you know, these gravitational waves, it’s a very recent discovery, a recent concept for us. The concept’s been around for a hundred years, of course, but you know, now that it’s a reality and we’ve observed gravitational waves, it’s very easy to think of the extreme events, black hole merges and you know, you can see this big ripple spreading out through space and time.
[00:46:31] But this idea of like a background gravitational hum, I quite like it. I think, you know, it was a really cool sort of discovery recently. And I think that there’s a, there’s a huge amount of information and data and stuff in there, which I think is just rich with,
[00:46:47] Jacinta: all right, give us your background hum.
[00:46:54] Dan: It’s so hard to catch the nuance though.
[00:46:55] Jacinta: Okay. Well, we’ll harmonize. Ready? Yeah. Three, two, one.
[00:47:02] Dan: Did you hear? There was a, there was actually a merger there.
[00:47:04] Jacinta: I heard it. I heard it. Well done. Just the vibe of the thing, right? We’re
[00:47:09] Dan: just vibing it out over here.
[00:47:11] Jacinta: Anyway. I would understand if you turn off at this point. Anyway. So we have had a little bit of a break where we kind of just ghosted everyone, so apologies for that.
[00:47:23] But Dan, how are you and what have you been up to?
[00:47:25] Dan: Uh, yeah, I feel like I always start the segment with the same thing, which is I’m busy as always. Uh, but no, I’m doing fairly well. Summer has arrived in Cape Town. This is a very exciting thing for Capetonians. It always delays by a month or two after you think it’s going to come.
[00:47:39] So everyone’s mood is vastly improved and, um, yeah. Doing well? You’re good. How are you?
[00:47:46] Jacinta: I am okay. Pretty good. Very tired. Very fatigued. This, uh, teaching semester has been really, really hectic, really chaotic and a lot of work. Probably one of the two most difficult things I’ve ever done academically along with a PhD.
[00:48:03] And honours. So, yeah, it’s been a lot, and so thanks for your patience while we’ve kind of had to take a break, but I think it was important for us to prioritise our mental health and not try and do too much, so that we’re still okay and we can come back to you when we’re ready and produce some more episodes.
[00:48:18] Dan: And another top tip for you if you are struggling with your mental health or anything else is to ask for help. So what did we do? We asked for help. Yay! And we’ve got a new producer, Francois. Yes.
[00:48:31] Jacinta: I was wondering where you were going with that.
[00:48:33] Dan: Francois Campher.
[00:48:35] Jacinta: That was a perfect segway, sorry for ruining it.
[00:48:36] Dan: Thank you. Thank you.
[00:48:37] Thank you.
[00:48:37] Um, yeah, Francois Campher has come on board as our podcast manager. The joke for me is that he will, you know, now also tell me what to do. So now there’s two people telling me what to do.
[00:48:47] Jacinta: And my joke is that I will now finally have someone to tell me what to do.
[00:48:53] Dan: Yes.
[00:48:54] Um, so yeah, we have Francois on board, which will hopefully streamline the podcast a little bit more.
[00:49:00] You know, he can, he can assist with, with the production of the podcast. And we’ll hopefully speak to him in the next episode, uh, briefly introduce you to our new podcast manager. So thanks, thanks Francois. Hi. Thank you Francois.
[00:49:12] And yeah, and thanks for, as Jacinta just said, your patience and hopefully we’ll be able to, uh, do better.
[00:49:20] Jacinta: Be more regular, I think. Yes, more regular episodes. Okay. I think that’s it for today. Yes. Oh, and I forgot to mention Tshimi, so she’s still a host. Don’t, don’t worry. She’s just busy at the moment and she’s going to give us an update on what she’s been up to in the next episode.
[00:49:34] Dan: Another useful strategy. Yes.
[00:49:38] Jacinta: All right. That is it for today. So thanks very much for listening and we hope you’ll join us again for the next episode of the Cosmic Savannah.
[00:49:45] Dan: As always, you can visit our website, thecosmicsavannah.com. We will have the transcript, links, pictures, and other stuff related to today’s episode.
[00:49:51] Jacinta: You can follow us on Twitter, or X, Facebook, and Instagram at Cosmic Savannah.
[00:49:57] That’s Savannah, spelled S A V A N N A H. You can also find us on YouTube, where audio only episodes are uploaded with closed captions, which can be auto translated into many different languages, including Afrikaans, isiXhosa and isiZulu.
[00:50:10] Dan: Special thanks to Professor Matthew Bailes for speaking with us today.
[00:50:13] Thanks to our new podcast manager, Francois Campher our social media manager, Sumari Hattingh. Our audio editor Jacob Fine. Also to Mark Wahlnut, music production Miha Warchek for photography. Carl Jones for Astrophotography, to Suzy Caras for graphic design. And thanks to Emil Meintjies for video creation.
[00:50:29] And thanks to Moses Makungu and Abigail Thambiran for transcription.
[00:50:33] Jacinta: We gratefully acknowledge support from the South African National Research Foundation, the South African Agency for Science and Technology Advancement, South African Astronomical Observatory and the University of Cape Town Astronomy Department.
[00:50:44] Dan: You can subscribe on Apple Podcasts, Spotify or wherever you get your podcasts and we’d really appreciate it if you could rate and review us and recommend us to a friend.
[00:50:52] Jacinta: We’ll speak to you next time on the Cosmic Savannah.
[00:51:00] That’s Cos That’s
[00:51:01] Dan: Cosmic, not S A V A.
[00:51:04] Jacinta: Too many mouth noises.
[00:51:06] Dan: I, um, I signed up for an Audible trial. Do you use Audible?
[00:51:21] Um, I’ve not got into audio books.
[00:51:24] Jacinta: I’m obsessive now.
[00:51:25] Dan: But anyway, there’s a, there’s a book I’m reading at the moment and I was just battling to get around to it. So I thought maybe I should just listen to the audio book as far so I can listen in the car or whatever. So I thought I’d went onto Audible and I listened to the sample, um, but the guy who’s since passed away, um, did the reading himself, the author who was like 80 or something.
[00:51:48] And just in the, just in the sample, which is supposed to sell the book, it’s just like,
[00:51:53] Jacinta: Oh no,
[00:51:55] mouth sounds.
[00:51:55] Dan: And I was just like, nope..
[00:51:57] I’ll read it myself.
[00:52:01] Jacinta: Fun anecdote.
[00:52:16] Dan: Back and relax, as we take you on a safari through the skies.
[00:52:19] Jacinta: I’m gonna try and do more water. I don’t know why my, it’s making it worse.
[00:52:23] Dan: I know, it is making it worse. Damn you, Jacob, with your ideas. I feel like dry mouth might have been better for me.
[00:52:30] Jacinta: No, it’s worse!
[00:52:30] Dan: It is worse.
[00:52:31] Jacinta: How does that make it worse?
[00:52:35] Dan: Where did you get your water from?
[00:52:36] Jacinta: I filter it from the tap.
[00:52:38] Dan: Maybe, um, um, maybe we just need to be self conscious.
[00:52:41] Maybe.
[00:52:42] Jacinta: Okay.
[00:52:45] Dan: So you might get fewer mouth noises, Jacob, but now you’ve got so much of us talking about mouth to listen through. So sorry about that one.
[00:52:54] Jacinta: Okay.
End of podcast:
365 Days of Astronomy
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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.
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Until next time let the stars guide your curiosity!