Episode 23: ThunderKAT - The Cosmic Savannah

with Prof Patrick Woudt

In Episode 23 of The Cosmic Savannah podcast, we are joined by the Head of Astronomy at the University of Cape Town, Professor Patrick Woudt.

Prof Woudt joins us to talk about an exciting project he is involved in using the MeerKAT radio telescope, namely ThunderKAT (The HUNt for Dynamic and Explosive Radio transients with meerKAT). ThunderKAT is looking for explosive things that flash in the radio sky!

The project has recently observed a black hole ejecting material at close to the speed of light out to some of the largest angular distances (separations) ever seen. These observations have allowed a deeper understanding of how black holes feed into their environment

Featured Guest

Featured Image:
South Africa has already demonstrated its excellent science and engineering skills by designing and building the MeerKAT radio telescope – as a pathfinder to the SKA. The 64-antenna array is located at the SKA site at Losberg in the Karoo, about 90 kilometres from Carnarvon. Credit: SARAO (South African Radio Astronomy Observatory).

Transcript

(By Brandon Engelbrecht)

Jacinta: [00:00:00] Welcome to The Cosmic Savannah with Dr. Jacinta Delhaize

Dan: [00:00:08] and Dr. Daniel Cunnama. Each episode, we’ll be giving you a behind the scenes look at the world-class astronomy and astrophysics happening under African skies.

Jacinta: [00:00:17] Let us introduce you to the people involved, the technology we use, the exciting work we do and the fascinating discoveries we make.

Dan: [00:00:25] Sit back and relax as we take you on a Safari through the skies.

Jacinta: [00:00:32] Hello everyone. Welcome to episode 23. Dan is joining us from home via Skype.

Dan: [00:00:38] Yeah. We’re all under lockdown. For the next little while, we’ll be having to do our recording via skype.

Jacinta: [00:00:44] Yeah, so of course, this is because of the coronavirus outbreak. South Africa has gone into lockdown now. Uh, like most of the world and we were considering whether or not to put out this episode weren’t we Dan?

Dan: [00:00:58] Yeah, but I think it’s, I think it’s good. I think that people are going to need some stuff to listen to and hopefully we can provide that.

Jacinta: [00:01:05] Yeah, I hope so too. Um, we all want a distraction. We all want to, you know, talk about something different and learn something new. So why not go ahead with that.

We’ll just have to put up with some low-quality sound from Dan’s end for a little while, but I think it’s okay and I’ve taken the recording equipment back to my house and I’m literally sitting in a blanket fort, which I made for myself for soundproofing.

Dan: Very professional.

Jacinta: Yes, definitely. I’m going to put a picture of it on the social media so you can have a look. I’m very proud of it. Right. Okay. So what are we talking about today, Dan?

Dan: [00:01:40] So today we’re joined by Professor Patrick Woudt he is the Head of Astronomy at the University of Cape Town here in Cape Town and he’s also the principal investigator for the ThunderKAT project, which is a large science project on the MeerKAT telescope.

Jacinta: [00:01:59] As we’ll talk about further when we chat to Patrick, the LSPs, as we call them, Large Science Projects are what MeerKAT is mostly going to be focused on during its run time and ThunderKAT is one of those.

It stands for The Hunt for Dynamic and Explosive Radio Transients with MeerKAT, if you can figure that one out, how they got to that acronym.

Dan: Just another contrived acronym

Jacinta: Oh, astronomers love it. Okay and so this is a survey in the radio with MeerKAT to look for transients.

Dan: [00:02:30] Yeah. So what is a transient?

Jacinta: [00:02:32] A transient is something that goes bang, basically an explosion, uh, in space. It’s something that wasn’t there before and then happens now. It is a transient event. So it happens sometimes and not at other times and one of these objects that ThunderKAT is going to be looking at is X-ray Binaries.

Dan: And what is an X-ray Binary?

Jacinta: Well, we did talk a little bit about it in episode 21 I think with Tanya Joseph, she talked a lot about these X-ray binaries. A binary is two stars going around each other and often one of these stars is a compact object. A compact object is something like a white dwarf or a neutron star or a black hole, something that’s, the fossil of the end of a star’s life and often it means that this compact object is going to be sucking material off its companion star, which is still a big normal star with gas on it and as this happens, it can release X-rays and then it’s called an X-ray binary.

Dan: [00:03:38] Yeah. So you’re basically looking at two stars, what was two stars orbiting around each other. One of them has now gone compact and the other one is just a regular star, right?

Jacinta: [00:03:48] Yeah, exactly and part of what ThunderKAT going to do is that they, there is several known X-ray binaries and there are X-ray telescopes looking at them and then MeerKAT is going to regularly look at the same binaries in the radio and check whether they’ve changed if they’re releasing more or less radio waves and then figure out what that means.

Dan: [00:04:09] And this is exactly what we’re gonna be talking about today right because they have already spotted one.

Jacinta: [00:04:13] They have actually found a new one while they were looking at one of these transients that they already knew existed. They spotted a new one and they’ve got a paper out on that and they also found one of these transients that they were monitoring doing something new and crazy.

And so they’ve published that in Nature Astronomy, which is quite a prestigious journal. They found that this object was emitting X-rays, so there was accretion happening, which means that the compact object is sucking in gas from its companion star, but then they found something special happening in the radio data with MeerKAT in that it was releasing jets.

So like huge ejections of material of matter, electrons and stuff near the compact object and it was being thrown out into space in one of the most energetic processes ever seen for this kind of event and being thrown out to one of the largest distances.

Dan: [00:05:09] Yes. I mean, it’s a very exciting discovery and great to see that these sorts of discoveries are already coming out of MeerKAT and some of the MeerKAT projects.

I think that we should probably speak to Patrick, who will tell us about all about it and also about the couple of other things we spoke to them about, such as the UCT Astronomy Department’s 50 year anniversary and the MeerLICHT telescope that we have mentioned once before.

Uh, which is another one of these multi-wavelength, a collaboration between MeerKAT and in this case, an optical telescope.

Jacinta: [00:05:41] Yeah. Great. Let’s hear from Patrick

With us, in the studio today is Professor Patrick Woudt, who is the Head of Department for Astronomy at the University of Cape Town. Welcome, Patrick.

Patrick: Hi Jacinta.

Dan: [00:05:57] Welcome to The Cosmic Savannah.

Patrick: [00:05:58] Hi Daniel.

Jacinta: [00:06:00] So Patrick, you are actually my big boss, I guess. Tell us about yourself.

Patrick: [00:06:06] I’ve been in South Africa for a long time. I did my PhD at the University of Cape Town, finished in ‘97 on large scale structures of galaxies under the supervision of Tony Fairall.

And I used many of the telescopes in Sutherland during that time. I went to ESO as a postdoc afterwards for two years and I came back to South Africa in 2000 and I’ve been here ever since, initially as a postdoctoral fellow and later as a senior lecturer, associate professor and now professor in the department.

Jacinta: [00:06:35] So you are from the Netherlands originally. But you’ve spent most of your career here in South Africa.

Patrick: [00:06:39] Indeed, yes. So I grew up in the Netherlands, did my first degree in The University of Groningen. Um, but then as I said, in 95, I came to South Africa.

Dan: [00:06:47] and you’re now the Head of the Astronomy Department, at UCT, right?

Patrick: [00:06:50] I am indeed. I’ve been for the last five years already.

Jacinta: [00:06:54] And you also have another role. You are one of the PIs, the principal investigator, of the ThunderKAT project, which is an LSP and that’s a “large science project” for MeerKAT. So we know from our previous episodes that MeerKAT is a big radio telescope in the Karoo in South Africa and most of the time we’ll be doing observations for these LSPs.

So these were proposed many years ago and went through a rigorous selection committee and in several of the large projects were chosen probably taking what, hundreds or thousands of hours, each and a ThunderKAT was one of those. So tell us about ThunderKAT. You’re actually the first PI of an LSP that we’ve interviewed

Patrick: [00:07:38] I’m honoured.

Jacinta: [00:07:40] So tell us about ThunderKAT

Patrick: [00:07:41] ThunderKAT is a large program on MeerKAT, which aims to study the accretion, the mass transfer of gas from one star to another and these are very compact binaries. So they complete one binary orbit, for instance, in about an hour, an hour and a half. If you compared it to the Earth going around the Sun, in one year or here you’ve got two stars, one very compact, the size of the Earth, the other one maybe the size of the Sun, completing one binary orbit in an hour and a half.

So that means they are very close together and when they’re that close together, they transfer mass and sometimes at mass when it’s transferred onto the compact central star, the most massive star, very exciting things happen. You get sort of explosions that throw material back into the interstellar medium and that sort of outflow, that mass ejection you can study in the radio.

Dan: [00:08:32] In this situation with compact binaries, the compact object is the more massive of the two right? And the Sun-like object or star-like object, that’s the one that’s losing its mass and slowly getting devoured by the compact object.

Jacinta: [00:08:49] Surely the compact object can’t be a normal star. If it’s the size of the Earth?

Patrick: [00:08:53] That’s right. So, so in my case, the objects that I study are the compact star is called what’s called a white dwarf, which is the end product of what our Sun eventually will become. But there are other compact stars like neutron stars and black holes, stellar-mass black holes that are even denser, more denser than the, than a white dwarf.

And so a neutron star has, has the mass of 1.4 times the mass of the Sun, but it’s the size of Cape Town, for instance, sort of 10 kilometres in size.

Dan: [00:09:20] So we’ve spoken previously about X-ray binaries. So X-ray binaries are basically a subclass of these compact binaries. You can have a binary system with a white dwarf as you are studying and then as you just mentioned, a compact binary with a black hole or a neutron star which are even more compact and these white dwarf boundaries that you are studying, they’re obviously not visible in X-ray?

Patrick: [00:09:46] They do have X-ray emission, but, um, so the different wavelengths trace the different components of such a binary. So in the white dwarf accreting binaries, um, the ultraviolet is the proxy for mass transfer.

If the ultraviolet emission is very strong, the mass transfer is very high. The radio is the proxy for outflow from the system through various emission mechanisms. In neutron stars, the proxy for accretion is not the ultraviolet, but even higher energy emission mechanisms, which is the X-ray. So when you study X-ray binaries, so you want to study them in X-ray to study the accretion onto the neutron star and in radio to probe the outflow that’s been induced by that accretion. Some of that material, excess material then gets thrown off the system.

Jacinta: [00:10:34] Okay, so there’s a normal star and then there’s a compact object, like a black hole or a neutron star or a white dwarf and you’re saying that some of the, the outer layers of this big star is being drawn onto this small compact object.

Patrick: That’s right.

Jacinta: If we see X-rays coming from this system, if we can detect the object in X rays, then that means that it is undergoing this process of accretion. So where the outer layers are being pulled onto the compact object and if we see it in radio waves, then that’s telling us that there is this sort of outflow, these big ejections of, of matter shooting into space.

Is that right?

Patrick: [00:11:13] That’s, that’s right.

Dan: [00:11:13] So what is the mechanism for these outflows? You’re talking about mass falling onto a compact star. Why do we expect an outflow?

Patrick: [00:11:21] Yeah, so there are different kinds of mechanisms in these binary systems, in the systems that I am most familiar with, the white dwarf accreting systems, you can have a cataclysmic outflow, which is a thermonuclear runaway on the surface of the white dwarf, which ejects the accreted material in an explosion and it blows it off at very high velocities, up to maybe a 10,000 kilometres per second, which is incredible; an incredible injection of energy. But they’re also more sedate ways of outflow and that, we haven’t talked about this yet, but the mass transfer from the companion star to a white dwarf normally goes through an accretion disk and sometimes that accretion disk gets into a higher state or hotter state, which allows the mass to flow more efficiently onto the white dwarf.

And you can have all sorts of wind mechanisms that blow material off. So you can have collimated winds creating an outflow.

Jacinta: [00:12:13] Okay. So you can have a thermonuclear detonation of the white dwarf, or you can have the star’s layers being pulled towards the compact object and in a disk sort of like a dinner plate shape, right?

Going around this compact object and then sort of trickling onto the compact object, right?

Patrick: [00:12:32] That’s correct

Dan: [00:12:33] So this isn’t happening all of the time right? These things are gonna have these little explosions, these outflows and then they’re going to disappear.

Patrick: [00:12:39] Yeah. So, so these binaries, they exist in a galaxy. There’s not many.

If you have a normal star, the fraction of having these sort of binaries requires a specific evolutionary pathway that leads to this close compactness at the most extreme and you can have two white dwarfs orbiting each other every five minutes, but those are extremely rare. The process of mass transfer is a very sedate one, it moves material into a disc, sometimes the disc goes into an outburst and the system brightens up. You can see that. For these cataclysmic variables, as we call them, that happens maybe once every month, in the process, and lasts a couple of days and then it goes back into a quiescent state. The nova outburst that, happens on the white dwarf that can happen on time scales of once every thousand years or, or once every few hundred years.

There are a few known in the galaxy that recur on a timescale of 20 years or 30 years, but typically that’s a much longer process.

Dan: [00:13:38] You’ve just published a paper on one such detection using MeerKAT. How exactly when these things are rare, how is, how is MeerKAT picking these up? Are you looking all the time for them or what is the strategy for finding these?

Patrick: [00:13:51] That’s an interesting question. So with MeerKAT, we’ve been using the telescope now since July 2018 a little over a year and a half and what we do in this particular program to study the X-ray binaries, so the accreting neutronl stars and black holes is to monitor a number of systems that are active and we know that they are active from the X-ray emission, what we discussed earlier.

So when you see X-ray emission, you know that there’s active accretion going on. So we follow active systems through X-ray monitoring. There are a number of X-ray satellites that pick these objects up and once we see them, we include them into our weekly monitoring list on MeerKAT once a week. We have a monitoring slot where we typically sample maybe four or five of these systems, for 10 or 15 minutes. It can be quite a short exposure because MeerKAT is so sensitive.

Jacinta: [00:14:43] Oh, wow. I didn’t realize it was so short. So this is the ThunderKAT project?

Patrick: [00:14:47] That’s right

Jacinta: [00:14:48] From past research and observations. You already know where these binary systems are, is that right?

Patrick: [00:14:53] Mostly, but some are new.

Jacinta: [00:14:54] Some are new, okay and then you can see them because they’re in the X-ray, which is picked up by a different telescope, is it SWIFT?

Patrick: [00:15:01] SWIFT is one of the telescopes that’s very good for monitoring. This particular one that we just published in Nature Astronomy is called MAXI J 1820+07 that just tells you where it is in the sky.

But the MAXI telescope is an X-Ray telescope that’s housed on the international space station.

Jacinta: [00:15:17] Cool! So this is obviously up in space. We need it to be above our atmosphere, which absorbs all of the X rays. All right, so these are, the telescopes are spotting these flashes of X-ray. So we know that something special is going on in these binary systems, probably some accretion and then, would this weekly monitoring program you have with MeerKAT, you go on and look at these systems with our radio telescope.

Patrick: [00:15:40] That’s right.

Jacinta: [00:15:40] Yeah and then what do you see?

Patrick: [00:15:42] We make images of these things. So we look at this variability or this time-domain astronomy, if you wish, with MeerKAT making images of the data and so we can spatially resolve phenomena that are related to such and such an event. So some of these systems, X-ray binaries are known when they are in this heightened state of mass transfer to eject a transient jet that comes from the system the jet moves at very high velocities, almost the speed of light and sometimes they appear to go faster than the speed up light, but it’s just a projection effect. What we do in this monitoring campaign is to study the behaviour of the X-ray binary during this bright state to understand how accretion is linked to outflow, how the accretion probed by the X-rays is linked to outflows as probed by the radio emission and in this particular case we saw the transient jet resolved in the image and move away at very fast, proper motions on the sky. So we could see the two jets on either side of the binary move very fast.

Dan: [00:16:45] A couple of things that a transient, a transient jet is something which just happens once. It happens for a short period of time?

Patrick: [00:16:53] So in these systems, when the X-ray binaries and acquires a mode of accreting it is thought to have a permanent jet that ejects particles and when the accretion switches on that permanent jet gets disrupted. So the accretion disk then dominates and a transient jet is sort of ejected at that point. So transient with transients we mean something that varies with time.

Jacinta: [00:17:15] Okay, so something that’s not always on, right? ThunderKAT has already put out its first publication, is that right? It came out in Nature Astronomy Journal on the 2nd of March this year, 2020 and Nature Astronomy is quite a prestigious journal. Meaning it’s a very important discovery. So tell us from the start, what this discovery was.

Patrick: [00:17:36] This particular observation made it into Nature Astronomy because it told us something new and something special about the bay X-ray binaries for a number of reasons. So we were looking at a X-ray binary that suddenly went into a high state of mass transfer.

We took images with MeerKAT over a long time about three months after the outburst, till half a year after the outburst and from that time series of images that we took, we could see two blobs, blobs, for lack of a better word, blobs on the sky, moving at very fast, apparent motion on this sky that was associated with this ejection of material.

Jacinta: [00:18:15] And do you know what the compact object was?

Patrick: [00:18:17] In this case, the compact object is a black hole, stellar-mass black hole.

Jacinta: [00:18:20] So it’s a black hole going around a normal star.

Dan: [00:18:23] The other way around.

Jacinta: [00:18:25] The black hole one has more mass than the other, right

Patrick: [00:18:28] Going around the common centre of mass.

Jacinta: [00:18:31] That’s our undergrad physics coming back to us. Okay so you saw these two blobs on the sky with radio and you mentioned that one of them seems to be superluminal, which is this beautiful word that means travelling faster than the speed of light. So what’s going on there?

Patrick: [00:18:48] The jet itself is moving close to the speed of light. And the approaching jet, because it’s closely aligned to our line of sight, it appears to be moving faster than the speed of light, but this is an apparent effect. It’s just a geometric effect that you can easily calculate. You could work out what the actual velocity is based on that. The real key aspect of this particular observation is that we observed it with MeerKAT which has 64 antennae based over an eight-kilometre baseline, giving you a specific resolution.

At the same time, we’ve also observed with the eMerlin radio telescope in the UK, which is an array of telescopes over the full length of the UK, giving us a much higher resolution image and so we were able to resolve the relativistic ejector on two different scales and by doing that, we can calculate the energy of the injection of energy into these jets.

And that wasn’t done before and we realized that the energy that was launched into these jets was much larger than we previously thought. So that was the new insight into the behaviour of X-Ray binaries and black hole ejections.

Dan: Relativistic ejector?

Patrick: Moving at the speed of light or close to the speed of light.

Dan: [00:20:04] You just throw that one in there hey? So, so basically this is the, so you’ve managed to measure the energy which this gas was thrown out of the system.

Patrick: [00:20:14] That’s right. By observing it with two different telescopes at the same time, but different resolutions and that allowed us that, that extra insight.

Dan: Very cool.

Patrick: So you mentioned earlier this was the first paper, but in fact, we have eight papers out already on ThunderKAT.

Jacinta: [00:20:28] Oh really?

Patrick: [00:20:31] Yeah.

Jacinta: Oh my goodness. I didn’t realize there are so many

Patrick: Exactly so there is a whole range of papers. We’ve discovered our first radio transient and it’s turned out to be a very unusual binary star and that paper was published also earlier this year by Laura Dressen, who’s a PhD student in Manchester.

Jacinta: [00:20:43] What was it? This weird system that you found.

Patrick: [00:20:46] In this case, it was a stellar binary of a star that is very active chromospherically, very active. So the Sun sometimes has chromospheric activity. This particular star is very active. It’s called an RS CVN binary named after its prototype. It has a 22-day periodicity and SALT was able to take spectra to confirm its nature and so with the radio, we could see it move up and down in brightness. Sometimes it wasn’t there at all. Sometimes it was, they’re very bright and so on this weekly monitoring schedule that we do, we are, we are hoping to find many, many more of these radio transients.

And this was the first one of its kind.

Dan: [00:21:27] You’ve detected all these things with ThunderKAT. For the one we were just talking about, the compact object. You followed up with another radio telescope and for this one, you were following up with SALT, is there a formal program for following up these things in different wavelengths for when you find a transient object, do you have the capacity to follow up with other telescopes immediately?

Patrick: [00:21:50] This is a very good question. The nature of this, this kind of astronomy is very much multi-wavelength astronomy. We mentioned earlier that the X-rays trace parts of the physics of these binaries, the radio traces another part of the physics.

In the optical with spectroscopy, we can characterize the binary using optical spectroscopy to see what the nature of the stellar component is or stellar companion is and so ideally you want to have a network of telescopes around the world that can follow these things simultaneously or quasi-simultaneously. Now, when we designed the survey to find all these new objects in the radio data trying to make MeerKAT and later the SKA has a transient discovery machine.

This particular question came up, how do we characterize these systems at other wavelengths? And so that’s when Paul Groot, who’s a colleague of mine, and Rob Fender and myself, sat together and said, well, let’s build our own telescope, the MeerLICHT telescope that will follow in real-time wherever MeerKAT is looking at the same part of the sky.

So we have an optical telescope that will always co-observe with MeerKAT. So if we find something, we will know in optical, what that part of the sky is doing and we can then relay that automatically almost directly to telescopes like SALT. There is a program on SALT that allows for immediate or very fast follow up of any, any unusual kind of behaviour.

Dan: [00:23:15] So that is basically that MeerLICHT, this optical telescope, tracks wherever MeerKAT is looking and the moment that something is identified as with MeerKAT, you see if it’s also visible in the optical.

Patrick: [00:23:32] That’s right.

Dan: and then if necessary, you can follow up with a larger telescope such as SALT

Patrick: That’s right.

Dan: [00:23:33] So then on what sort of timescale are you analyzing this data? Is the ThunderKAT data analyzed instantly?

Patrick: [00:23:39] Almost instantly. The aim is to do it in real-time. What we’re doing at the moment is that once the data gets taken from the Karoo, from where the telescope is, it gets moved to the archive, the South African Radio Astronomy Observatory archive and we pull it into our cloud-based compute resource at the university.

There’s the Inter-University Institute for Data-Intensive Astronomy (IDIA) and that is a cloud-based computing facility where we analyze all our data and within an hour of the data being taken, we move it across. That process goes quite quickly depending on how, how large the data set is and then we can immediately reduce and analyze our observations.

So within 24 hours we will know what’s going on.

Jacinta: [00:24:23] So you need a supercomputer cluster to be able to process all of this data?

Patrick: [00:24:28] That’s right.

Dan: [00:24:29] And is this automated or does somebody have to be sitting there?

Patrick: [00:24:31] It is fairly automated. There are a number of scripts that we can run and that that sort of then takes it in in a semi-automated way.

The goal is to develop this into a fully automated pipeline where we work in near to real-time. To see what’s happening so we can respond in near-to-real time. The optical data gets also transferred from Sutherland in this case, to the same compute infrastructure at the university and there an image gets ingested once it’s completed.

So every minute at the moment, we’ve got a minute cadence on the optical telescope, a minute repeat timeframe. So at the moment, every new image gets ingested into the database, automatically reduced and that’s then injected into a database of sources all over the sky.

Dan: [00:25:18] So does the feedback work the other way around too? If MeerLicht observes something that’s transient does it tell MeerKAT?

Patrick: [00:25:25] Eventually, yes, at the moment we are still testing out our transient detection algorithm on the MeerLICHT in the optical sky. Uh, you have to be careful for what’s called false positives and they can be artefacts in the data analysis that might look like a transient, but in fact, it’s, it’s an artefact of the data reduction.

And you have to be very careful not to issue false alerts. But eventually once that is working and once we’re finding transients in the optical database, we would like it and in some cases to feed that back to MeerKAT, but that needs to go through a program, maybe a ThunderKAT program where we have a target of opportunity where we can point the MeerKAT telescope and, but if a transient is occurring in the field, in the MeerLICHT of data, we most likely will have MeerKAT data on that field because the two telescopes are tied together in that sense.

So we should be able to see what’s going on in the radio at the time where we see an optical.

Jacinta: [00:26:22] And that’s really impressive that you’ve essentially attached this optical telescope to the radio and it tracks exactly the same position as whatever the radio telescope’s looking at at that moment. Has this been done before?

Patrick: [00:26:34] Not, not as far as I know. So the unusual thing here is that the MeerKAT telescope has a very large field of view, which is great for finding new transients. It increases your probability of finding something in the field of view because you just looking at a much larger field of view. But traditionally optical telescopes have a much smaller field of view.

So to match that MeerKAT field of view, which is typically one square degree of the sky. So imagine a grid of two by two full moons together to match that in the optical. We needed to design a wide-field camera that is both a simplistic and operation for robotic operation as well as giving you that wide field of view.

And so the design then led to the MeerLICHT concept, which has a single electronic camera underneath. With 110 million pixels, which can be read out in seven seconds. So, it’s a lot of pixels can be read out in seven seconds. So we take an image of the sky every minute and then seven seconds later we can take our next image.

The data flow from that is, it’s not too high. Although you mentioned earlier, the ThunderKAT data flows is quite large, at the moment it’s about a hundred gigabytes for every one hour of observation and that’s in the low time resolution, a low-frequency resolution that can easily be up to a factor of 30 more.

Jacinta: [00:28:02] I imagine that because you have, it has to have such a wide field of view to match MeerKAT. You’d have to have some sort of trade-off? Probably sensitivity?

Patrick: [00:28:11] Yeah, so, so we can do the optical design of the telescope that that simultaneously has that wide field of view. You optimize very quickly to a telescope size of about 0.6/0.7 meters.

So that’s smallish for an optical telescope. But within a minute of observation, we’d reached down to a magnitude of 21. 21st magnitude, for point sources for star-like sources, which is at this stage, the optimal limit for a spectroscopic follow up on SALT. The bigger the telescope, the more sensitive.

But with our current design within the minute we, we basically have an optimal follow-up for SALT and we can reach a very faint level of brightness.

Jacinta: [00:28:52] Okay. It’s got a pretty good sensitivity, or I guess brightness limit, which is the equivalent word in optical astronomy. Not radio. So this is going to say there was something seen with MeerKAT we saw at the same time in the optical. This is an interesting thing. Now let’s go and look at it again with SALT, which is a more sensitive, bigger telescope, right?

Dan: [00:29:13] So you seem to be pretty well set up to detect these transients and we, I mean, we were just chatting earlier about one you’ve detected and you have detected a few now with MeerKAT, we really are expecting some new discoveries. There are things we can’t expect to find. In your mind and in the field of transients, what are you expecting? What is exciting with MeerKAT?

Patrick: [00:29:37] The exciting thing in time domain astronomy is to look at things that vary on very short timescales. I think over the last 10,20,30 years, we very well characterize things that vary on a timescale of days or weeks or months. The Nova explosion, the Thermonuclear explosion on the white dwarf that I mentioned earlier, those are fairly well studied, but we know very little about how the objects in the night sky vary on timescales, less than a day on time scales of an hour or a minute or even below a second.

There’s very exciting objects called fast radio bursts and that gives you a single pulse of maybe 10 milliseconds in, in time that comes from cosmological distances in galaxies, far, far away and we want to characterize those sources. We are now discovering, astronomers are now discovering these in quite large numbers, but still with fairly poor localization in the sky, although that’s getting better.

So one of the things that MeerKAT and MeerLicht can do is to identify and locate them, but also locate the optical counterpart to those fast radio bursts, the host galaxy in which these things reside. These are once-off events if you’re not on the sky when, when this happens, you would have missed it. So by having the wide field of view, you have a greater probability of finding these things

Dan: [00:30:57] and nobody has observed that yet?

Patrick: [00:30:59] Some have been observed some of these systems are repeating sources and we don’t quite know why. Some are repeating and some are not repeating. But for some of the repeating fast radio bursts, they have been localized quite well and there are host galaxies associated with them.

Jacinta: [00:31:14] Well, we have so many questions about transients because we know so little about it and we can talk about it all day, but I know you’re a busy person.

We have to let you go soon. Before that, I’d like to just talk about the University of Cape Town Department of Astronomy because it’s celebrating a special anniversary this year.

Patrick: [00:31:28] That’s right. Thanks, Jacinta for asking that. This year, it’s our 50th anniversary of the astronomy department at the University of Cape Town. It was established in 1970 as a formal department, versus astronomy departments around the world which actually are part of a physics department. Ours grew out of the physics department at UCT the director of the observatory in Cape Town was an honorary professor of astronomy in the department of physics. But at the time when the observatory changed into the South African Astronomical Observatory and the Sutherland Observatory was being established in the Northern Cape in South Africa and the University of Cape Town decided that it was time to set up its own department of astronomy, which is now 50 years ago. So we’ve, we’ve been doing great astronomy in the last 50 years and there’s a lot of excitement, of course with SALT and MeerKAT to look forward to and we’re celebrating this wonderful milestone with a lot of activities, public talks, outreach events and so on.

Jacinta: [00:32:30] And I’m a part of the current generation there as a postdoc at UCT, are there any of the celebration events that some of our listeners, particularly those in Cape Town can participate in?

Patrick: [00:32:40] We’ve had a number of things already. We had a public talk by the president of the International Astronomical Union recently.

But throughout the year, we’ll host a number of talks and events. We will advertise them on our website and on our Facebook site as well. We will post them to the public and given the close history that our department has with the South African Astronomical Observatory who is also celebrating a major milestone this year. We will see how to coordinate the 200 anniversary of the SAAO with activities around the 50th anniversary of the Astronomy Department.

Jacinta: [00:33:11] Oh, great. Well, Dan’s sitting right next to you and he’s running those

Dan: [00:33:15] Patrick and I have spoken already

Jacinta: [00:33:17] Okay.

Dan: [00:33:19] we’ve, we’ve come up with some ideas which we will implement.

Jacinta: [00:33:22] And Patrick, are there any significant moments that happened in the last 50 years of the UCT Astronomy Department?

Patrick: [00:33:30] Sure. That’s a, that’s a big question.

Dan: [00:33:33] Well, at least what you can remember.

Jacinta: [00:33:36] Well, you gave a really great talk at the start of the year about the history of the department and there were quite a few

Patrick: [00:33:42] there. Lots of wonderful milestones. So we, we’ve had great people, great students coming through the department, people who’ve gone on to find significant posts across the country, across the globe in astronomy.

In terms of the work that we’ve been doing over the last 50 years. It’s quite interesting to see that the astronomy department started with, in 1970 was searching for supernovae and galaxies and studying compact binaries and the astrophysics of these cataclysmic variables that a lot of new insight has been gained in those, in those areas and that the astronomy department is still doing a lot of work in these areas, particularly, I think the highlight has been the inclusion of radio astronomy over the last 15 years with, with MeerKAT on the horizon. We’ve become specialized in radio astronomy, both in the stellar astrophysics side, but also in extra-galactic astronomy. The study of neutral hydrogen, for instance, is one of the strengths in the department I’m very proud of.

Jacinta: [00:34:41] Awesome and just lastly, before we let you go, are there any other final messages you have for listeners.

Patrick: [00:34:47] So, so one of the things that’s happened in the astronomy department over the last 15 years, since 2006, is that we restarted our major in astrophysics and that’s grown and grown.

And this year we have 25 3rd year students which is the largest group that we’ve ever had and we organize open days and so my message, to people who are out there who consider a career in astronomy is be curious, be inspired by what goes on in the sky. There’s a lot of things still to discover.

MeerKAT is a fantastic machine, so for the next generation of astronomers in South Africa and the learners at schools, if you want to know what the Universe is made out of you’re in the right place to come and study that.

Dan: [00:35:30] Great. Thank you very much for joining us, Patrick. We really appreciate your time.

Jacinta: [00:35:34] Thanks, Patrick.

Patrick: [00:35:35] Great pleasure.

Jacinta: [00:35:35] Talk to you again soon.

Dan: [00:35:37] Thank you. When you make another discovery

Jacinta: [00:35:49] All right. I think this concept of MeerLicht is very, very cool to have an optical telescope that’s essentially attached to the radio telescope so that it’s looking at the same place as the radio telescope at all times.

Dan: [00:36:02] Yeah, I, I mean, we’ve talked about ThunderKAT, that awesome discovery, there’s going to be a lot more from MeerKAT, but getting more and more wavelengths involved yeah and I think it’s just going to be another fascinating avenue of astronomy to go down. So the MeerLicht telescope is, is definitely gonna make some awesome discoveries and contribute to, to some of the discoveries we’ve already made. You know, a very, very exciting project. Very cool and as you said, the first time that this has been done somewhere in the world.

Jacinta: [00:36:31] Yeah, because usually, one telescope in one particular wavelength will spot an interesting object and then send out an alert to all other telescopes, which will then look at it. But in the time it takes for that alert to be made, the transient occurrence may already be finished. So it’s really great that you can have at exactly the same time, both radio and optical observations.

Dan: Yeah, you should note that sometimes those alerts go out in seconds

Jacinta: Sure. Yeah.

Dan: [00:36:58] and telescopes, can follow up, but the seconds are sometimes not enough for these transients.

Jacinta: [00:37:03] Yeah, exactly. All right. I guess so the 50th-anniversary celebrations of UCT and the 200th-anniversary celebrations of the observatory, is that going to be, I guess that’s going to be impacted a bit by this Coronavirus lockdown?

Dan: [00:37:19] Yeah, for sure. So we’re not really sure how this is going to go and where we’ll be in October most of the celebration were planned, but at the moment we are talking about various contingency plans, potential postponements, we planned a large astronomy festival. First of all, we are looking at maybe doing it virtually, which will be quite cool actually.

It’s definitely concerning, but the least of our worries right now, I think everyone’s health is is a bigger concern and trying to keep safe.

Jacinta: [00:37:48] Yeah, exactly. Everyone’s health and safety is by far top priority.

Dan: [00:37:53] Yes. Keep safe out there guys

Jacinta: [00:37:55] Yeah. Wash your hands, keep social distancing. You know the deal. All right. Good luck everybody and we’ll hope to chat to you again soon.

Dan: All right. See you later.

Jacinta: Okay. Dan’s logged off Skype, so that leaves me to do the credits. Thank you very much for listening and I hope you’ll join us again for the next episode of the cosmic Savannah. You can visit our website, thecosmicsavannah.com where we’ll have links related to today’s episode.

You can follow us on Twitter, Facebook and Instagram @cosmicsavannah. That’s Savannah spelled S. A. V. A. N. N. A. H. Special thanks today to Professor Patrick Woudt for speaking with us. Thanks to Mark Allnut for music production, Janus Brink for the Astrophotography. Lana Ceraj for graphic design and Thabisa Fikelepi for social media support.

Also to Sumari Hattingh, Brandon Engelbrecht and Lynette Delhaize for transcription assistance. We gratefully acknowledge support from the South African National Research Foundation, the South African Astronomical Observatory and the University of Cape Town Astronomy Department to help keep the podcast running. You can subscribe on Apple Podcasts, Spotify, or wherever you get your podcasts and if you’d like to help us out, please rate and review us and recommend us to a friend. Stay safe everyone and we’ll speak to you next time on The Cosmic Savannah.