Episode 46: A crash of clusters

Above: Scrolling transcript. Static transcript below.

with Dr Kenda Knowles

In this episode, we are joined by Dr Kenda Knowles who is a Research Fellow at Rhodes University, South Africa. Kenda speaks with us about her work as an observational astronomer working on the MeerKAT.

Kenda has just released a beautiful new dataset called the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). The Survey contains images of the radio emission from 115 clusters of galaxies!

The survey has detected very faint emissions from these clusters which can teach about how these clusters form and evolve and the gas and magnetic fields within them. They also contain a wealth of data still to be explored!

Here we see radio evidence of a powerful merger taking place between two or more massive groups of gas and galaxies. These structures (a so-called ‘halo’ near the center and two ‘relics’ surrounding it are seen in the galaxy cluster MCXC J0352.4-7401) trace the positions and strengths of cosmic magnetic fields and electron populations travelling near the speed of light. This MeerKAT image spans approximately 10 million light-years at the distance of the cluster, and is sprinkled with point-like radio emission from even more distant Milky Way-like galaxies. Adapted from K. Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights” (Astronomy & Astrophysics, in press). Image credit: SARAO.


Two giant radio galaxies (more than one million light-years from end to end) at the center of a large group of galaxies in the cluster Abell 194, revealing the presence of relatively narrow magnetic filaments in the region, as well as complex interactions between the radio emission from the two galaxies. The MeerKAT radio image is shown in orange, with an optical image dominated by normal galaxies shown in white. Adapted from K. Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights” (Astronomy & Astrophysics, in press). Image credit: SARAO, SDSS



This week’s guest

Episode Links

Kenda’s Twitter: https://twitter.com/kilokilok9

Rhodes Centre for Radio Astronomy Techniques & Technologies : https://ratt.center/

Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights“, accepted for publication in Astronomy & Astrophysics.

The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.


Transcript by Moloko Makwetja and Justine Crook-Mansour.

[00:00:00] Dan: Welcome to The Cosmic Savannah with Dr. Daniel Cunnama

[00:00:09] Jacinta: and Dr. Jacinta Delhaize. Each episode will be giving you a behind-the-scenes look at world-class astronomy and astrophysics happening under African skies.

[00:00:18] Dan: 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] Jacinta: Sit back and relax as we take you on a safari through the skies.

[00:00:33] Dan: Welcome to episode 46.

[00:00:35] Jacinta: Hi everyone. Today, we will be speaking with Dr. Kenda Knowles, who is a research fellow at Rhodes University, and we will be talking about the MeerKAT Galaxy Cluster Legacy Survey. But first Daniel, how are you?

[00:00:48] Dan: I’m well, thank you. Looking forward to a break over Christmas. How are you?

[00:00:52] Jacinta: I just called you Daniel. It felt really weird because I have never called you that before. I always call you Dan.

[00:00:58] Dan: I always introduce myself as Daniel, but then kind of, I don’t know… I leave it up to the person to decide whether they want to call me Dan or Daniel. You chose Dan.

[00:01:06] Jacinta: I think I only call you Daniel when you’re in trouble.

[00:01:10] Dan: Which is seldom or if ever.

[00:01:13] Jacinta: Of course. Anyway. Yes. Good. I’m good. I’m good. I’m here in Australia still. And I apologize if in the background you can hear my dog snoring. He has decided to be my office mate and he has fallen asleep on the job and he is sitting down beside me snoring. So, sorry if you can hear that.

[00:01:32] Dan: That’s a bit of charm.

[00:01:36] Jacinta: Yeah. So this week, I’ve been attending the SARAO bursary conference 2021. So that’s the South African Radio Astronomy Observatory. And it’s a conference of all of the radio astronomy students and postdocs and young researchers in South Africa. And it’s held every year. This is the 15th one, and it’s a very exciting one.

Same as last year. Well, similar to last year because there’s a lot of results coming from the MeerKAT telescope, which is of course one of the world’s best radio telescopes and is located in the Karoo in South Africa, and is starting to produce a lot of amazing results. And we’ve been talking about a few of those on this podcast, so it’s great to be able to hear a few more and get a few ideas of who else we might like to talk to on the podcast.

[00:02:20] Dan: For today’s episode, we’re speaking to Kenda Knowles, as you mentioned. You spoke to Kenda. I actually know Kenda from many years ago, and she’s also from Pietermaritzburg, where I grew up. And I was doing my MSc while she was doing her undergrad. And I used to tutor her or I dunno what do you call it when you… I don’t know… you… the… you demonstrate the prac like, so the physics practicals. I used to be the…

[00:02:45] Jacinta: Oh.

[00:02:45] Dan: The tutor for her.

[00:02:47] Jacinta: Okay. You were her lab demonstrator.

[00:02:48] Dan: Yes. Exactly.

[00:02:48] Jacinta: Or her prac demonstrator.

[00:02:49] Dan: Mm-hmm.

[00:02:49] Jacinta: Oh, okay, cool. Oh, wow. I didn’t realize that. Small world, small world.

[00:02:56] Dan: And Maritzburg is a very small town.

[00:02:59] Jacinta: Well, yes, I imagine so. Yeah, no, I talked to Kenda all about galaxy clusters, and the great work that she and her team have been doing with the telescope. And I know Dan that you actually did your PhD on galaxy clusters. So, you might cringe at a few of the questions I asked Kenda. I didn’t know much about it. Sorry about that. But yeah, I guess we can just maybe just briefly go through what galaxy clusters are and why they’re important. But Kenda will tell us more about that.

I thought we could start with discussing collective nouns for things, including galaxies. You don’t look impressed, but I’m gonna plough ahead with this. Okay. So Dan…

[00:03:43] Dan: Okay.

[00:03:43] Jacinta: Do you know…

[00:03:44] Dan: Go on.

[00:03:44] Jacinta: Do you know what the collective noun for crows are? What do you call a bunch of crows?

[00:03:49] Dan: A murder.

[00:03:49] Jacinta: A murder, indeed. Very good.

And here’s a South African related one. What do you call a bunch of rhinos?

[00:03:57] Dan: A clash?

[00:03:59] Jacinta: A crash.

[00:04:01] Dan: Oh, I was close.

[00:04:02] Jacinta: Very close, very close. I think that’s brilliant. A crash of rhinos. What about kangaroos?

[00:04:11] Dan: Mm, no, I don’t have that.

[00:04:13] Jacinta: I wanted it to be something like a skip, but it’s a mob. A mob of kangaroos.

[00:04:17] Dan: A mob. Oh, well that sounds about right.

[00:04:20] Jacinta: All right. What do you call… what’s the collective noun for a bunch of galaxies?

[00:04:24] Dan: A bunch?

[00:04:25] Jacinta: No, a group. A group of galaxies. So that’s like if you’ve got a few galaxies bound by gravity. And what do you call…

[00:04:33] Dan: Yeah.

[00:04:34] Jacinta: What’s the collective noun for a bunch of galaxy groups?

[00:04:37] Dan: I know where you’re going. You want me to say cluster, but if we’re talking about gravitationally bound, then correct.

So, what gravitationally bound means is that when you have a galaxy, all of the stars within that galaxy are held together by gravity. So they all have their own gravity. They’re pulling together this dark matter, and the stars can’t escape that galaxy. They’re bound by gravity.

A group of galaxies are, as you would imagine, a few to many galaxies who are quite close together and they also have gravity, they’re attracting each other and they’re bound in a larger sense. So they have space between them, but still they’re pulling in on each other. So they can’t escape that group.

A cluster of galaxies, it’s either, you know, a larger object or bound area of space with these groups of galaxies within it… many groups of galaxies, you know, potentially thousands of galaxies. The galaxies don’t necessarily have to be in groups and they obviously will be some groups and maybe some sedated galaxies within the cluster.

But all of those galaxies are again, gravitationally bound, sort of pulling towards each other in a cluster. So that’s a cluster of galaxies. Whether that’s the collective noun, I think is a matter of English more than physics. Because…

[00:06:02] Jacinta: Oh, boo. Play a long Dan. It’s a group of groups.

[00:06:07] Dan: Okay. We’ll go with it.

[00:06:07] Jacinta: It’s a group of groups. So it’s a collective noun. Okay. That’s my idea. And I’m sticking to it.

[00:06:15] Dan: Okay.

[00:06:15] Jacinta: Anyway, I think the listeners can get from this… that, you know, clusters are a bunch of galaxies, a whole big bunch of galaxies, which may or may not be in groups. You might have some galaxies that are in groups. You might have some that are not. But they’re all bound gravitationally together into this big cluster. And you don’t just have galaxies in groups, right… in clusters. There’s other stuff in clusters?

[00:06:40] Dan: So in between galaxies, there’s something called the intergalactic medium. Which is very diffuse gas. I mean, we are talking very diffuse, a few atoms maybe per square metre or cubic metre. And in a cluster or in a group of galaxies, this intergalactic medium is obviously denser than in the void of space. So there’s an intergalactic medium in a group in between the galaxies.

And there’s also something called the intracluster medium in a cluster where, you know, you have this medium, this diffuse gas, which is pulling the cluster. Kind of very hard to detect, and really not dense. So, we think of air as diffuse, but air is incredibly dense gas. We’re talking sort of very few atoms.

[00:07:25] Jacinta: I mean, clusters can collide with each other too, can’t they?

[00:07:28] Dan: Yeah. So in the formation of larger scale structures in the galaxy or in the universe, there’s… sort of galaxies don’t form in isolation as we’ve discussed, you know, they form in groups and clusters, generally. And those clusters, with their massive gravity wells, keep pulling in other galaxies and other matter. And when sort of two clusters eventually pull hard enough on each other, or for long enough, those clusters can join and merge into a larger cluster. You know, that’s how we go from groups to clusters. There’s a sort of continual merging process.

[00:08:05] Jacinta: And when these massive clusters collide, they can cause big shocks, heat up the gas and cause all of these crazy patterns that you can see with radio telescopes.

[00:08:15] Dan: Yeah, exactly. And I think that’s what we’ll be talking to Kenda about. She’s an observational astronomer. So, she’s working with MeerKAT to detect these interactions between clusters of galaxies. But as you said, these intracluster medium, even though it’s diffuse, the particles do interact and often they’re highly energetic. So they have a lot of energy and they’re moving quite quickly. And when they interact, you can think of it as… maybe as two waves crashing together and interact and well up and to make a sort of a larger wave or a bit of a splash, I guess.

[00:08:51] Jacinta: I mean, crashing clusters. So, what do you call… What’s the collective noun for a whole bunch of clusters? Maybe it can be a crash of clusters. Taking us back to the rhinos. Can we please call this episode a crash of clusters?

[00:09:07] Dan: Sure. You can have it. Whether it takes off or not, we’ll see.

[00:09:16] Jacinta: All right. Anyway, I think we should maybe hear from the expert now. So, let’s hear from Kenda.

With us today, we have Dr. Kenda Knowles, who is a research associate at Rhodes University. Welcome Kenda.

[00:09:36] Kenda: Hi Jacinta. Thanks for having me.

[00:09:38] Jacinta: Thank you very much for being here. Kenda. Can you quickly just tell our listeners who you are, where you’re from, and how you got into astronomy?

[00:09:45] Kenda: So, yeah, as you’ve really introduced me, I’m Kenda Knowles. I have my PhD in astronomy and cosmology. I’m from a city in South Africa called Pitermaritzburg. I grew up outside of a city with awesome night skies, but I only really got into astronomy my third year of undergraduate, when I found out about the South African SKA project. And it’s been astronomy ever since. It’s been great.

[00:10:09] Jacinta: Excellent. So can you just tell our listens briefly, what is the SKA?

[00:10:13] Kenda: So the SKA, the Square Kilometer Array… this is a project to build the world’s largest radio interferometers. So what that means is that it’s a collection of radio telescopes, or radio antennas that all get linked together to simulate one giant receiving area for radio waves. And it’s aimed to be… will be the most powerful radio telescope that we’ve ever had.

[00:10:37] Jacinta: And in the meantime we have MeerKAT, of course.

[00:10:40] Kenda: Yes, and MeerKAT is wonderful. I love working with MeerKAT data. I’ve been working with MeerKAT data since about 2018 now. Gosh, it’s been three years, and so MeerKAT is the South African precursor to the SKA. So the SKA is being shared between South Africa, and the African continent and Australia… Australasia, I suppose. And so each of those two countries basically built their own precursor instrument to test things like the engineering, but also to show that they can do the science and be able to host this massive project like the SKA.

So MeerKAT is South Africa’s. It’s 64 dishes in our Karoo desert. And it is extremely sensitive and has just been producing some wonderful science over the last couple years.

[00:11:28] Jacinta: Speaking of amazing science results, Kenda, I know that you have recently had a paper released using MeerKAT data. And so you lead, I believe the MeerKAT Galaxy Cluster Legacy Survey, is that correct?

[00:11:40] Kenda: Yes, it is. And we shorten it to the MGCLS because we like our acronyms.

[00:11:45] Jacinta: We definitely like our acronyms in astronomy. .

[00:11:50] Kenda: So this is a quite a large project. It’s actually a observatory-led program. So they took the data and decided which targets to observe. But essentially what it’s built up to is a collection of 115 targeted observations of galaxy clusters. And so each target was observed for quite a long time. So between 6 to 8 hours, and what that means is you get really nice deep images of each of these patches of the sky.

[00:12:20] Jacinta: Okay. And why were these patches of the sky chosen? What’s in these patches?

[00:12:24] Kenda: So at the centre of each patch is a galaxy cluster. In case the listeners don’t know what that is… So with the structure formation in the universe, you know, you start small with stars. Stars form together, or rather get bound together to create a galaxy, and then galaxies can then also be bound together to create these very large structures that we call clusters. Very ingeniously because it’s a cluster of galaxies.

And so these structures are very, very interesting, both for people who care about astrophysics. So plasma physics, you know, how do galaxies evolve, what’s happening with magnetic fields in the region. Cosmic ray, electrons, protons, you know, particles traveling very, very close to the speed of light. But it’s also… they’re also very interesting for cosmology because when we look at how many of them they are, how they’re distributed in the universe, they can tell us something about how our universe began and has evolved and maybe what might happen to it in the several millennials still to come.

So they’re very, very important objects to study for a very broad range of sciences.

[00:13:30] Jacinta: So you mentioned that these galaxy clusters are huge. They’re not just galaxies themselves. They’re clusters of galaxies. They’re groups of groups of galaxies. So these must be really enormous. How big are we talking here?

[00:13:43] Kenda: So when we’re working with them, we talk about mega parsec scales, just because they’re so large. But what it comes down to in light years is, you know, a couple millions of light years from one end to the other, if not more.

[00:13:56] Jacinta: And you mentioned that, like in these clusters, there’s glowing plasma. Is that right? And what is plasma?

[00:14:02] Kenda: So, yes. So galaxy clusters have the galaxies that we spoke about, but they also have large amounts of gas that’s are in between all the galaxies. And that’s essentially what this plasma is. It’s glowing, generally very hot gas with, you know, magnetic fields also intertwining throughout everything.

And you also then have dark matter that we can’t see, but dark matter is actually what is making up most of the mass of these systems. But of the things that we can see, it’s the galaxies and this hot gas.

[00:14:33] Jacinta: All right. So we’ve got magnetic fields, we’ve got plasma, we’ve got highly charged particles traveling really fast, we’ve got galaxies. So what does all of this look like? What do you see when you look at your data that you’ve collected with MeerKAT?

[00:14:46] Kenda: So with MeerKAT, because it’s just such a sensitive instrument and these particular observations were carried out for a long period of time, we see a lot of galaxies. Many of which will be part of the cluster, but many of them will be between us and the cluster and also behind the cluster. So those show up as, you know, point sources in our image, they just look like nice little spheres. Some of them have very interesting structures if they have jetted emission, which you see as sort of faint diffuse regions in the image. Then in some of the clusters, we actually see the hot gas shining in the radio. So it’s not in all the clusters, but in many of them we see the sort of very faint, diffuse region where the cluster is. And sometimes there’ll be large regions on the edges of the cluster as well.

[00:15:37] Jacinta: Yes. So I’m looking at your press release now, which is gorgeous. It’s got some images from your survey, and I’m looking at one that I think it’s a cluster.

So you can see lots of what you said with point sources, which just means like a dot of bright light. Really doesn’t look like anything, just actually a dot and there’s, I mean, there’s hundreds of them, if not thousands. And then you’ve got some slightly bigger dots, which I am thinking are bigger galaxies or more nearby galaxies. And then you’ve got this kind of glow in the background all over the place behind all of these point sources. Is this the glowing gas that you were talking about?

[00:16:12] Kenda: Yes. So in the one I think you’re talking about in the centre, there’s this big sort of glow that’s kind of looks like an ellipse, and then you… on either edge of those, you’ve got like a big arc shape that’s also glowing. So yes, the central bit is what we call a radio halo. And what we think this is from is when galaxy clusters bash into each other. So everything in the universe, we believe it builds up through merger activity. So small things merge into bigger things, et cetera.

You also get these massive clusters merging together with other massive clusters. And when this happens, you get a lot of energy that gets deposited into the environment. And this can accelerate the particles in this gas. So electrons, protons, and they can accelerate them to speeds – quite close to the speed of light. And when you also have magnetic fields, which we mentioned earlier, when you have those two things together, you get what we call synchrotron radiation.

And in order for this diffuse glow to cover the scales that we see… so that central glow is again, probably about a million like years across. In order for the electrons to keep emitting and to keep it the speeds that they need to be, there has to be this extra energy that keeps on being deposited. And we think that comes from the merger.

[00:17:36] Jacinta: Okay. So listeners can’t see this image and it’s really hard to describe it, but we’re gonna put it on the website. So do check it out. It’s a stunning image. It can be quite confusing at first, if you don’t know what you’re looking at. So what you’re saying, Kenda, I think, is that everything can collide in the universe. And so even groups of groups of galaxies. So galaxy clusters of… I don’t know how many galaxies can be in a cluster. Thousands?

[00:18:00] Kenda: Yes, definitely.

[00:18:01] Jacinta: So big clusters of thousands of galaxies. Those two can collide with one another, and all of the gas that’s between all of the galaxies kind of collide together as well, and glows. Is that what this kind of fuzzy, faint, glowing part of the image is?

[00:18:17] Kenda: Yes. Well, that’s what we think. There’s lots of different theories about how it might come about, but the one that seems to be most successful at the moment, at least for the diffuse glow in the centre, the one that looks like a blob is that, yes.

When you get these massive galaxy clusters merging together, all this energy gets deposited and you get a lot of turbulence happening because obviously it’s a very dynamic environment. There’s lots happening, lots of moving parts. And so there’s a lot of turbulent energy in this gas from both clusters. And it’s that turbulent energy that’s driving the particles and the gas to these relativistic speeds. So near the speed of light. And they need to be that fast in order to create the radio emission.

[00:19:02] Jacinta: So you said that this diffuse. Diffuse means kind of like a fuzzy cloud-looking thing. This is called a radio halo. What do we learn by studying the radio halo in a galaxy cluster?

[00:19:12] Kenda: So we can learn several things. One of the key points is about the magnetic fields within the cluster. So, magnetic fields are things. They’re everywhere. We think they’re everywhere. But surprisingly, we don’t know very much about them. And so studying these radio sources, as you say, diffuse blobs…. I call them diffuse blobs a lot because they’re intimately linked with the presence of magnetic fields. How bright they are in the radio depends on how strong the magnetic field is.

So if we can observe them, the first thing we know is that magnetic fields are there. The second thing that we can find out is how strong is the magnetic field. And if we start looking at these in different types of clusters, so ones that are very young, ones that are a bit older, massive ones, less massive ones, we can then start to see if there’s a difference in the magnetic field in these different types of clusters, and that can try help us understand how magnetic fields in the universe evolve.

[00:20:11] Jacinta: So if it’s glowing more, it tells you that the magnetic field in the cluster is larger, right?

[00:20:17] Kenda: Is, yeah. Is stronger.

[00:20:18] Jacinta: It’s stronger. Okay. So people will know what magnets are. We have magnets on our fridge and these are gigantic magnetic fields on the scales of not just galaxies, but on the scales of clusters of galaxy. So there’s this huge cosmic magnetism. I’m scared of magnetism on this scale because I don’t understand it. And it’s really complicated. It’s really hard to work with. So, where is this magnetic field coming from and what does it mean?

[00:20:47] Kenda: So these are some of the questions that we want to figure out. So there’s various theories about where cosmic magnetism comes from.

So I don’t work with that at a huge level in my day to day, but the main ones is that magnetic fields could be what we call primordial. So they existed right at the beginning, you know, at the start of time. And then they grow in strength as universe ages. There’s also theories that magnetic field growth or how they get stronger could be related to more dynamical activity, rather than just a general aging process.

But that’s one of the things that we really don’t know, and we need more observations in order to be able to answer these types of questions.

[00:21:33] Jacinta: So, this is actually the mystery and why you’re doing this sort of… part of why you’re doing this sort of work is to figure out where these magnetic fields came from.

[00:21:40] Kenda: Yes, that’s definitely one of the questions that we’d like to answer.

[00:21:43] Jacinta: Amazing. And when I say I’m scared of magnetic fields, I’m not scared as in, they’re not gonna hurt us. You know, these galaxy, these clusterized magnetic fields, they’re not gonna hurt us. I’m scared of it because it makes me nervous because we always have to consider magnetic fields in our research. And it’s just so hard that it always scares me away. But, now I’ve heard and you’re correcting me if I’m wrong, that you can study these magnetic fields through the polarization of the light that you’re looking at. Is that correct?

[00:22:12] Kenda: Yes. That’s the other thing that we can do. So not just on how bright the emission is, but we can actually study the alignment of the magnetic field, how it’s aligned, you know, with respect to the observer, so that’s us. And also what we’d call the fractional polarization. So that is how strongly polarized is it. Is it maybe a few percent? Is it many percent? Is it not polarized at all? And looking at that can also help us understand more of the structure of the magnetic field rather than just its strength.

[00:22:43] Jacinta: What does it actually mean for light to be polarized? Does this have something to do with like polarized sunglasses, for example?

[00:22:50] Kenda: So, yes. I mean, it’s quite a complicated concept, but to try to keep it simple; light arrives at a particular angle. So the wave is traveling at a particular speed, but it’s also got a particular angle compared to the observer.

And when you, so polarize glasses, for example, they will cut out waves, hitting the glasses at a certain angle and let in others. And if you twist those glasses, you tend to see that it then shuts out different light. So polarization of any light. So radio is still light. It’s just at the very low energies.

And so it’s a similar concept of when you observe polarization in the images that you make, you can observe an angle. You can also observe a amount of polarization and that’s related to the direction at the wave is traveling when it arrives at us.

[00:23:45] Jacinta: Great. Thanks for that, Kenda. I know it’s a difficult concept to try and get across, but I think that was a great explanation. So we’ve talked about the, what the galaxy clusters are. We’ve talked about the radio halo and how that’s teaching us about the magnetic fields. And now I wanted to ask you about these weird brightly glowing, giant arcs that are in the picture. So these are kind of like these huge curved stripes of bright light through your images around the outside of the cluster.

What are they?

[00:24:10] Kenda: So, these are what we call radio relics. So it’s a similar type of emission. It’s still very fast electrons, and traveling in a magnetic field over very, very large distances. But these have a slightly different formation mechanism; compared to the halo that we talked about before. So these relics, as you’ve said, you know, they’re on the outer edges of where the cluster is, and they have these nice arc shaped form.

These are related to shock activity in the cluster. So again, related to the merger. So, if you think you have two massive things bashing into each other, you’re going to have shockwaves traveling through the gas, traveling through the plasma. So these shockwaves are compressing the gas, and it’ll also be compressing the magnetic fields.

And so when you have massive shocks, you sometimes get these radio relics structures, which are related to these shocks, driving that energy that we said, we needed the electrons to be very, very fast. And there has to be some energy to drive that. So we believe for these relics that energy comes from the shock activity. Which is why you see them generally to be quite nicely aligned with the edges of the cluster, where you would see the shocks, in for example, x-ray observations of the gas.

[00:25:29] Jacinta: Wonderful. So huge shocks of these collisions. What can we learn from these radio relics?

[00:25:36] Kenda: So from the radio relics, they can tell us something about that shock itself. So how strong was the shock? And if we know that we can sometimes work backwards to try simulate the actual merger itself.

So was it just one thing bashing into another thing? Were there many smaller components, all coming in together from different directions? Again, it can tell us something about the magnetic field. So we talked about polarization. Relics tend to show polarization unlike the halos, and this is, because the magnetic field is getting compressed and it gets very nicely aligned at the edge of this arc shape structure.

And when you have a nice aligned magnetic field, you tend to see polarization. Whereas in the halo, because it’s such a turbulent environment and things are happening in all sorts of different directions. Well, there definitely are magnetic fields, but you tend not to pick up polarization because there’s no nice alignment of the magnetic field, cuz everything’s getting messed up during the turbulence.

So with relics, we tend to see very nice structured polarization. which tell us that there’s very nice structured magnetic field. And again, from that, we can tell things about the strength of the magnetic field, the structure of the magnetic field. You’ll see, in the image, the very bright one at the bottom left of the image.

If you look closely, there’s actually filaments that you can see, it’s not just one fat stripe. There’s filaments of radio emission that you can see. And those filaments will be tracing magnetic field filaments as well. So that relates back to the structure of magnetic fields and how they get distributed throughout this cluster environment.

[00:27:12] Jacinta: So Kenda, this is amazing. It’s just such a treasure trove of information that you’ve got here. Like what does it feel like when you look at these images?

[00:27:21] Kenda: Sometimes I just stare at them because I find them very pretty and very beautiful.

[00:27:26] Jacinta: Yeah.

[00:27:26] Kenda: But I think it’s also a.., An immense sense of achievement, not just for myself, but this was a massive team effort.

So, I might be the first name on the paper, but it took a lot of different people to make sure that this project got published. So that goes all the way from SARAO, taking the data, deciding what things to look at, to the people who were heavily involved with taking the data and making it into these beautiful images that we see.

And then once we have the images, then comes all the exciting science stuff of analyzing them and figuring out what we can do. And the thing I think that I like most about these data sets, is that it’s not just one science goal. So, in the paper that we published, we sort of gave highlights of several different types of science that you can do with these images.

So, we’ve talked a lot about this diffuse stuff, and that is my main interest. These diffuse emission in clusters, but you can also look at all those points of bright light that you swa. So, all those galaxies and use them to study things like star formation in the cluster. So in the ones where there’s this, you know, massive merger activity and all this energy, does that impact all the star forming in the actual galaxies themselves?

We can look at some of the galaxies that we see with these beautiful large structures to them. So they have their own jets, their own filaments, and we’ve been seeing structures that we’ve never seen before. So, they’re not just pretty, they’re also really, really interesting for our science and they’ve both helped us answer questions that have existed for a while, but the very exciting bit is that they’re just creating more questions as well.

And I think that’s what I love most about these data sets.

[00:29:08] Jacinta: That is a very exciting thing that your data is introducing new questions. I mean, that’s really what science is all about going, and looking at something and finding something that you didn’t even know was there. The unknown unknowns is so exciting.

So what is it about MeerKAT that makes this dataset so amazing? I mean, you mentioned that you’re finding things that you had never seen before. And when I asked you about MeerKAT, you smiled so enormously and most people smile, that give this huge smile, whenever we talk about MeerKAT and I certainly do.

Yeah. What is it about MeerKAT that’s special that lets you do this sort of work?

[00:29:43] Kenda: So with MeerKAT, there’s two things that really come together to make it a really powerful instrument for these types of studies. And the first one is the design of the array. So, where did they put the antennas when they put them on the ground?

So, there are some arrays out there, like the VLA where the antennas can move. MeerKAT is fixed, so they put the cement in, and then that’s where your antenna is, for the rest of its life. And they were very, very careful when they designed the array so that they grouped a lot of them together.

So what we call the core, there’s about a one kilometer diameter core of antennas, which is roughly, I think about 60% of the antennas were in this core. So they’re very tightly packed. And what this means is that you get very, very good sensitivity to large faint stuff on the sky. So, when we are talking about all these diffuse structures, the halos, the relics, that’s exactly what they are.

They they’re patches of very large scale, but very faint emission. And so MeerKAT is immediately very sensitive to that in a single observation. But they didn’t just worry about the core because if you’re sensitive to large scale stuff, that’s great. But as we see in these images, the sky is made up of a lot of small things.

And if you can only see things on the large scale. So if you think about smoothing something out or blending things together, you’re gonna miss a lot of that fine detail information which you need. And so MeerKAT, in terms of where the antennas are, there’s also and the rest, the other 40% or so of the antennas are more spread out.

And so you get these long separations. And what that means is that you get sensitivity to small things on the sky. So basically the array layout gives you the simultaneous sensitivity to big and small things to be able to probe a whole bunch of different scales in one single observation. So that’s the first thing.

The second thing is that, the engineering was fantastic and they just built it incredibly well. And it’s an incredibly sensitive instrument. So in terms of the receivers, the antenna gains and all the, you know, the technical engineering side of things, MeerKAT was designed to have certain specifications.

The astronomers said, to do our science, we need to have an instrument that is this sensitive. And then the engineers came along and basically doubled the sensitivity. So they made MeerKAT twice as sensitive as anyone was expecting. Which is great because it means you don’t have to look at something for as long to get a sensitive image.

So let’s say you wanted to gauge a certain sensitivity, and you said, I need 10 hours with the telescope to do this. With the way the engineers built it, you can get that same sensitivity in maybe six or seven hours, which means we can pack in more science. So it’s those two things that just make MeerKAT such a phenomenal instrument, particularly in the south where there isn’t really a lot in the radio other than South Africa and Australia now. There’s obviously been a lot of development driven by the Square Kilometer Array. And so that’s opening up the southern sky to us that we’ve never been able to see at these depths or with these sensitivities.

[00:32:51] Jacinta: Absolutely. Are you, looking forward to the SKA?

[00:32:55] Kenda: I am. I’m also a bit intimidated by the SKA in terms of how much data we’re going to be getting, and also how sensitive they’re going to be. I mean, we see these new images from MeerKAT and ASKAP as well from Australia. And, you know, we’re already starting to see things that we weren’t expecting to see. And so that’s opening up the new questions when the SKA comes along. So there, we’re talking about, you know, not 64 dishes, but thousands of dishes and over much larger, you know, separation.

So we’re gonna be really be able to get down to the very, very fine detail. It’s a bit mind-boggling to me about what we’re going to be seeing. So from the science side, it’s incredibly exciting; from the technical side, incredibly daunting, because with all that amazing power comes a lot of..,

[00:33:44] Jacinta: Responsibility,

[00:33:45] Kenda: responsibility to get the data, to do something. Yes. So, there’s a lot of very smart people already working on and trying to prepare ourselves for the SKA because the amount of data we’re gonna get through, we need to find ways to handle it in order to get this amazing science out, that we’re so excited to do.

[00:34:04] Jacinta: Yeah, absolutely. Absolutely. And what’s next for you Kenda? Now that you’ve got this paper out, you’ve published the data. I assume this is public and anyone can play with the data. What do you wanna do next?

[00:34:16] Kenda: So many things. So yes, this data is definitely public, you know, there’s, we have a website for it and you can access all the data through there directly, or just follow the links in the paper. Because the main goal of this legacy survey is exactly that, it’s supposed to be legacy data that will be available to the entire global community to do whatever science they want to do with.

So, from my side, there’s still projects using this data that we’ve got ongoing. As I said in the paper, we sort of showed highlights of things. So we’ve got some projects already underway about just going into a slightly deeper level. And there’s some students that we’re getting in for, you know, their masters and PhD projects and whatnot.

I also have other MeerKAT data, which is also on clusters. But the difference is that these are short observations rather than these very long ones. And so I have all that data that I’m busy working with and working with people both in South Africa and overseas on just trying to get as much out of MeerKAT as possible before it gets sort of amalgamated into the Square Kilometer Array.

[00:35:20] Jacinta: Oh, wow. So no lack of things to.

[00:35:23] Kenda: Definitely not. With MeerKAT, there never is a lack.

[00:35:27] Jacinta: Awesome. Thank you so much for joining us today. Kenda, before you go, do you have any final messages for listeners?

[00:35:32] Kenda: I would just say that, you know, I don’t know who the listeners are in terms of they’re you know, amateur astronomers or just ideal listeners, but keeping your mind open to the universe and what’s out there and trying to understand, even in a tiny way everything that’s going on, I think is a great thing to keep our minds and our imaginations active. So, thank you for listening to these types of podcasts.

[00:35:56] Jacinta: Absolutely. Thanks, Kendra. And if listeners want to find you online on social media, are you there?

[00:36:01] Kenda: I’m on Twitter. So, I don’t use it very much. I use it for rugby mostly, but they can find me on Twitter @kilokilok9. Otherwise they are the Rhode pages. There’s a page there, and I think my email address is on there as well.

[00:36:17] Jacinta: All right. And we’ll link to all of those on the website. Thank you once again, Kenda for joining us. This has been fantastic.

[00:36:23] Kenda: Cool. Thanks very much for having me. This’s been fun.

[00:36:33] Jacinta: When I was saying I was, scared of magnetic fields. What I actually meant was intimidated. I’m intimidated by the study of magnetic fields. It’s very difficult.

[00:36:42] Dan: Yes, it is very difficult. I think the physics of magnetic fields is very difficult. It’s not something we understand on a sort of theoretical level, what magnetic fields are and how they work in terms of the fields themselves.

We can model that, we can understand it. I think that the difficulty comes in these environments that we are looking at in astronomy, right? So, we are looking at intergalactic mediums or, you know, in galaxies or in clusters, intracluster media. And we don’t know what effect the magnetic fields have on those interactions.

So, you know, we understand how magnetic fields work, but we don’t understand how they work in these very extreme environments.

[00:37:26] Jacinta: And I feel like I didn’t quite do justice to the explanation of polarization. Do you a better explanation for us, Dan?

[00:37:35] Dan: It’s funny. I feel like that too.

[00:37:38] Jacinta: Hey,

[00:37:43] Dan: I think you explained it fairly well. I mean, with polarized lenses and your glasses. I think that the way I picture it, you kind of have to have a picture in your mind of how these things work. When you think of light, we can think of the light as a photon or a particle, but it has a wave nature.

It has a wave function, and the light is sort of oscillating in a sort of sinusoidal wave. And some of those photons are moving up and down. Some of them are moving left and right, and every other angle in between. So, you know, if you think of the face of a clock, all of those possible angles are coming towards us.

And if you have sunglasses, like you mentioned, it will cut out all of the angles except for one. So you’ll just get the up and down wave coming through, and that’s what a polarized lens does. It takes away all the glare and all these other elements of life. And when you’re looking at polarized light from a radio galaxy, you can detect that, you know, the light will be polarized in one way more than another.

And we have to understand why that happened. And generally why that happened is because there’s a magnetic field, and a magnetic field basically turns those angles or you know, eliminates some of the angles so that the light has a preferential kind of up and down, or left and right based on the gas that’s come from where the gas has traveled through.

How was that?

[00:39:11] Jacinta: Yes, that was a great explanation. Thanks Dan.

[00:39:15] Dan: Okay. I hope so. Yeah, so, I mean, it was fascinating to hear Kenda talking about the observational astronomy that’s happening now with MeerKAT, being such a sensitive instrument, you know, we can delve deeper. I can dust off my PhD, but you know, when I was doing my PhD, like the MeerKAT didn’t exist and, you know, I was doing the theoretical aspect and we need observations to try and compare our theory too, and try and understand how these structures are forming and what they really look like.

You know, having more and more data means that we can improve and refine our theories. And, you know, it’s just really exciting to hear these progress going on.

[00:39:57] Jacinta: Yeah, and I love the concept of a legacy survey. So that means that it’s meant to be this data set, which is so good and contains so much stuff that it’s like a treasure trove that people will be able to dig into for many, many years to come and find more and more stuff.

So, yeah, I think that over the years, this data set is gonna produce a whole bunch of research, a whole bunch of papers, and looking forward to seeing the results from those.

[00:40:22] Dan: Okay. So, just to note, we are almost in December, I think when this comes out, we’ll be well into December. And we will be taking a little bit of a break, both Jacinta and I over the first of season. And we will be back in January with small.

[00:40:38] Jacinta: Yes, indeed. And while we’re away, we hope that JWST will successfully launch. As we discuss that all in episode 35, we were mentioning how the launch date was December 18th. But since then it has been pushed to December 22nd. And by the time you’re reading this, who knows when the launch date will be, but hopefully it’s in.., It sneaks in, in 2021. And we really hope it’s a successful launch. So hopefully by our next episode, we can bring you the updates, with how that’s going.

[00:41:07] Dan: Yes. I wanted to wish all our listeners a very happy and joyful JWST launch.

[00:41:14] Jacinta: Yes. Indeed. And I will wish our listeners are very happy and a very safe and healthy holiday season. And we will see you back here in, 2022.

[00:41:25] Dan: Thanks as always for listening and we hope you’ll join us on the next episode of The Cosmic Savannah.

[00:41:32] Jacinta: You can visit our website, thecosmicsavannah.com, where we’ll have the transcript, links, pictures and other stuff related to today’s episode.

[00:41:40] Dan: You can follow us on Twitter, Facebook, and Instagram @cosmicsavannah. That’s savannah is spelled, S A V A N N A H.

[00:41:47] Jacinta: Special thanks today to Dr. Kenda Knowles for speaking with us.

[00:41:51] Dan: Thanks to our social media manager, Sumari Hattingh, and our audio editor, Jacob Fine.

[00:41:56] Jacinta: Also to Mark Allnut for music production Michal Lyzcek for photography, Carl Jones for astrophotography, and Susie Caras for graphic design.

[00:42:04] Dan: We gratefully acknowledge support from the South African National Research Foundation, the South African Astronomical Observatory, and the University of Cape Town Astronomy Department.

[00:42:12] Jacinta: 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 or recommend us to a friend.

[00:42:21] Dan: And we’ll speak to you next time on The Cosmic Savannah.

[00:42:38] Jacinta: I mean, I do have to be honest, I missed most of it because the zoom chat froze, but I trust that it was a great explanation.

[00:42:45] Dan: Oh, brilliant. I mean, it was excellent. I promise.

[00:42:50] Jacinta: Well, I look forward to hearing back this episode, and indulging in the explanation.

Carl Jones for astrophotography and Susie Caras for graphic design. Tonka. Stop it. He’s digging up the carpet. Hang on sorry, my dog..,

[00:43:13] Dan: What is his name?

[00:43:14] Jacinta: His name is Tonka, like Tonka truck. We didn’t name him. He’s a rescue.