Episode 24: HIRAX

with Prof Kavilan Moodley

Episode 24 features Professor Kavilan Moodley who joins us to discuss another exciting project in radio astronomy in South Africa, HIRAX!

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio telescope array that will map nearly all of the southern sky over a frequency range of 400 to 800 MHz. The primary goal of HIRAX is to measure baryon acoustic oscillations (BAOs): these are remnant ripples in the distribution of galaxies that originate from primordial sound waves that existed in the early universe.

This can be used for charting the expansion history of the universe and for shedding light on the nature of dark energy.

All-sky map of the Cosmic Microwave Background temperature as obtained by the Planck space telescope.  Credit: ESA
A Rock Hyrax or “Dassie”

This week’s guest:

Episode Links:
HIRAX: https://hirax.ukzn.ac.za/
Planck and the CMB: https://www.esa.int/Science_Exploration/Space_Science/Planck_overview

Featured Image:
The HIRAX Prototype dishes at the Hartebeesthoek Radio Observatory, South Africa

Transcription – By Sumari Hattingh

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

Jacinta: [00:00:07] and Dr. Jacinta Delhaize. Each episode, we’ll be giving you a behind the scenes look at world-class astronomy and astrophysics happening under African skies.

Dan: [00:00:16] Let us introduce you to the people involved, the technology we use, the exciting work we do, and the fascinating discoveries we make.

Jacinta: [00:00:24] Sit back and relax as we take you on a Safari through the skies.

Hello. Welcome back to episode 24

Dan: [00:00:40] yeah, welcome back.

Jacinta: [00:00:41] Yeah, Dan’s still on Skype. How’re you doing over there?

Dan: [00:00:45] Yeah. All right. Locked in the house with little kids. So if you hear the kids in the background, you know, apologies for that.

Jacinta: [00:00:52] Yeah. And I’m still in my blanket fort and I have no little kids here, so I just made one. I have no excuse. We’ve expanded it now it’s got two rooms.

Dan: [00:01:01] Do you stay in it even when you’re not recording?

Jacinta: [00:01:05] Yup. And we’ve added fairy lights now as well. All right. So what are we actually going to talk about today?

Dan: [00:01:12] We are joined by Professor Kavilan Moodley, who is from the University of Kwa-Zulu Natal, who you actually interviewed at the South African Radio Astronomy Observatory Bursary Conference, and he’s going to be talking to us about dark energy and an instrument they they’re building called “HIRAX”.

Jacinta: [00:01:30] Yeah, exactly. So, as you said, I was at the South African Radio Astronomical Observatory – SARAO – Bursary Conference in December last year, the start of December, which was held in Durban, which was really great to go visit because I haven’t had much of a chance to explore South Africa yet. Just Cape Town and a few other places.

But, so Durban was really cool. And, it’s more or less like the South African National, like annual conference, of Radio Astronomy. And so there’s radio astronomers there from all over the country. So it was a great opportunity to get some interviews with some people, not from Cape Town. And Kavi is one of those. He’s the Professor at the Department of Astronomy UKZN, and he’s one of the people leading the charge in building a new telescope called HIRAX.

Dan: [00:02:20] Yeah, we’ve spoken a lot about MeerKAT; we’ve mentioned a couple of the other instruments, which are happening….at the SKA. But in addition to MeerKAT, there are all of these other instruments which are also getting built, which have different little niches that they work in.

They work in slightly different niches. They look at different things in space and different frequencies, different wavelengths, and have different science cases. This is one of those different instruments, which is also going to be built in South Africa.

Jacinta: [00:02:52] Yeah, so it’ll be made of 1000 dishes and they’re each going to be six meters in diameter. And HIRAX stands for the Hydrogen Intensity and Real-Time Analysis eXperiment. So another contrived acronym from astronomers.

Dan: [00:03:11] It’s quite a fun one because if you don’t know what a hyrax is; a hyrax is a little, well, it’s not a rodent. But you can think of it as a rodent – it’s a little thing that looks a bit like a bunny, but doesn’t have long ears. It’s brown, and they exist here in South Africa. They run around on rocks and on mountains and things, and they’re very sweet, and we call them “dassies”. But their proper name is a “hyrax”.

Jacinta: [00:03:41] Yeah, and it’s a super cute logo with a little, a little dassie on it for those from Australia. It kind of looks like a marsupial, even though it’s not; like a little quokka that’s on, like only on all fours and doesn’t stand up. So that’s how I would describe it. Well, we’ll put a picture on our website.

Dan: [00:03:59] The other thing that is always said about a dassie or a hyrax is that its nearest relative is an elephant. It goes all the way back on its own branch, all the way back to the common ancestor of the elephant, and the hyrax, which is pretty strange.

Jacinta: [00:04:14] That is strange. The dassie can be found in the Karoo and the Karoo is where the telescope is built. So we’re looping back to astronomy there.

Dan: [00:04:23] Yeah. And then, as you said, there are thousands of these little dishes and they’re six meters across, so they’re not as big as the MeerKAT ones, which are 13 and a half meters across.

And they’re also a lot simpler. So they don’t have the same demands in terms of the surfaces or the instrumentation. And that means that it’s a very cheap experiment. And we can build houses with these things, for a fraction of the process; a MeerKAT dish.

Jacinta: [00:04:51] Yeah, exactly. But it’s not built yet. Just like the SKA is not built yet. There is a prototype that’s somewhere near Johannesburg, I think.

Dan: [00:04:58] Yes, Hartebeesthoek. The original Radio Astronomy Observatory in South Africa was in Hartebeesthoek, which is just outside Pretoria in South Africa, and there’s a large radio dish there, but now there’s the prototype for the HIRAX, and that’s just to test the instruments.

To try and get a concept together of what it’s gonna look like and then use that to try and raise funding to actually build this thing.

Jacinta: [00:05:28] Yeah. And other than the dishes themselves, one of the main differences between HIRAX and SKA is that the HIRAX dishes are all going to be kind of in a high density, small area, so they’re all going to be clumped quite close together.

Now, you might remember that radio astronomers always talk about baselines, which is the distance between two of these dishes and short baselines mean that the dishes are closer together. If you have dishes closer together, your telescope is more sensitive to larger scale, so you can see things that are larger on the sky.

Whereas if you have, your telescopes are very far apart, long baselines, they’re more sensitive to things that are small on the sky; small structures. But HIRAX wants to see the largest structures on the universe, and that’s why it’s got a high density of very short baselines. And they want to see large scales because a lot of the science case for this telescope is cosmology.

So I don’t know Dan. Well, so Kavi does explain that a bit, but it’s kind of, well, I guess it’s the universe on the larger scales. And I guess we need to start from the Cosmic Microwave Background or CMB in order to explain that. So, Dan, do you want to explain what the CMB is?

Dan: [00:06:43] So I’ll, I’ll take a stab. So cosmology is basically the study of the very largest scales, as Jacinta said, we’re not looking at individual galaxies. We are looking at the clusters of galaxies and beyond that supercluster – how the matter in the universe is distributed on the very, very large scales – are these clusters, there’s voids where there’s no galaxy.

And why is the matter distributed like that? What you want to do is, see where these large dense regions or under dense regions formed from. Where did they originate from? Why is there more matter in one place than somewhere else? And one of the ways we can work that out is by measuring this Cosmic Microwave Background.

If you look in the microwave wavelength or frequency, you can see all around the earth, and this has been mapped in quite a lot of detail, first led by Kobi satellite, but most recently by the Planck satellite. And everywhere you look there is microwave radiation, which is coming from the very, very early universe, and it has tiny fluctuations in terms of the color or temperature of that light. And those tiny fluctuations make up what’s called the Cosmic Microwave Background and those tiny fluctuations are the hint. as to why some regions will be dense and some regions will be under dense. So by mapping this very early universe and these fluctuations, we can see where matter would fall and on what scales – where it comes from and in what form; in what scale. So we can measure in quite a lot of detail what sort of scales the fluctuations are on; on the Cosmic Microwave Background.

And then if we can measure by doing a galaxy survey of our local universe or the larger universe, we can see whether those correlate, if there are a lot of galaxies on one sort of scale and the surveys, does that correlate to these initial fluctuation? And it does. A Nobel prize was awarded for this.

This was a major discovery in recent astronomy or cosmology. And this gives us a very good idea of the distribution of matter within our universe.

Jacinta: [00:09:07] Yeah, exactly. That’s a challenging thing to explain, but I think you did great. I would just add that the thing that you want to pin down is the characteristic scale of the baryonic acoustic oscillations, and that essentially is like putting a ruler onto the universe at each time. So as the universe is aging, you’re trying to put a ruler against it at all of those times and see what the typical size of certain things is. So as you mentioned, you might do a galaxy survey and you might measure the typical distance between galaxy clusters, for example. But what HIRAX is going to do – it’s not going to look at galaxies. It’s more going to look at neutral hydrogen gas, which can exist between galaxies and therefore it could be a better tracer or a different tracer of this typical scale or typical size. And the reason why you want to do – why HIRAX is doing that – is actually to study dark energy because it’s this dark energy, which is accelerating the expansion of the universe.

And that of course was another Nobel prize to several people, including professor Brian Schmidt from our community in Australia. Shout out to Brian. So you’ve got dark matter, which is essentially adding gravity and pulling everything towards each other. But you’ve got dark energy, which is kind of like anti-gravity or negative gravity and pushes everything apart.

And this effect has changed in its strength over the history of the universe. So at the beginning, sort of after the Big Bang, it was relatively weak compared to the other forces, but now it seems to be dominating a lot more. So HIRAX is trying to look at the hydrogen, measure the typical length scales, and therefore make some conclusion about dark energy and maybe that lets us figure out what it is.

Dan: [00:11:00] So we basically get a different view of a different time in the universe. So the Cosmic Microwave Background is as early as we can look at 380,000 years after the Big Bang. And we can look at these scales and fluctuation. Now we can look at the galaxies now and see those scales.  But by looking at the neutral hydrogen with HIRAX, we can look at a time in between so we can look at the early universe beyond the CMB before galaxies formed, before a lot of the galaxies formed, and as you said, then we can get an idea of what the strength of dark energy was in those times and how the matter was distributed.

Jacinta: [00:11:42] Exactly. But that’s not the only thing HIRAX can do. It’s also looking at transients. Dan, do you remember what a transient is from the last episode with Patrick?

Dan: [00:11:53] I do. Okay. A transient is basically something which is out of varying with time in terms of its brightness, or another sort of factor. Or it’s something which goes – something which happens very briefly, once-off, and doesn’t occur again.

Jacinta: [00:12:11] Yeah. And in the previous episode 23 – talking to Patrick – we were talking about one type of transient object, which can be an X-Ray binary, where you’ve got black holes or whatever, sucking stuff off their partner stars. But in this case, HIRAX is looking for fast radio bursts or FRBs for short, and we don’t really know what this is at all, but it happens on millisecond scales.

So there’s just a sudden millisecond flash of bright radio light, and HIRAX is going to try and figure out what they are. And it’s an ideal telescope to do this because it’s going to see a wide area of the sky all at the same time. So if these things are quite rare and quite brief, you need to be looking kind of everywhere at the same time in order to spot them to have a good chance of spotting them.

But because they’re quite small, you also have to have good angular resolution as you need to be able to see things on small size scales. But we’ve already mentioned that HIRAX is going to have short baselines, and so it’s actually going to be better at looking at large scales, but they’ve come up with a way to solve that, which is the VLBI – very long baseline interferometry – which we spoke a lot about in episode,… what was it, back in season one, episode five with the EHT imaging of the black hole? Do you remember Dan?

Dan: [00:13:30] I may not remember which episode it was. I do remember discussing it.

Jacinta: [00:13:34] We were talking to Roger Dean and we went into a lot of details. If you want to know more about VLBI, you can go back to that episode, but basically you put a few telescopes out really, really far away. So long, large base lines away from your central core of telescopes. And these can be called outrigger stations. And that gives you the ability to see these shorter spacings on the sky. And so you’ve got a better chance of picking up these FRBs and to localize them, which means to figure out exactly where they’re coming from because some telescopes can see them, but say, okay, it’s coming from somewhere in this area, and with HIRAX, you want to be able to pinpoint exactly where in that area it’s coming from, and that’s going to give you a better chance of figuring out what’s causing it.

Dan: [00:14:21] Yeah. So we’ve given a good overview, I think of what HIRAX is going to be doing. We should probably hear from Kavi himself, who is the PI of this project, and he will be talking to you, Jacinta, about what it’s gonna do.

Jacinta: [00:14:35] All right, let’s hear from Kavi.

…music playing…

With us now is Professor Kavi Moodley from the University of KwaZulu Natal, welcome Kavi.

Kavi: [00:14:48] Thanks Jacinta.

Jacinta: [00:14:49] Kavi, tell us who you are, where you’re from, what you do.

Kavi: [00:14:52] Yeah. So I’m a professor at the University of KwaZulu Natal, as you mentioned to the listeners. My name is Kavilan Moodley. I’m interested in cosmology and astrophysics. So, I do research in this topic here in Durban.

Jacinta: [00:15:07] Okay. So tell us about the research group at the, at UKZN.

Kavi: [00:15:10] Yeah. So we’ve been – the research group at UKZN has been growing over the last few years. We now actually have set up an astrophysics research center at the university and we have a number of undergraduate students, postgraduate students and postdocs.

And our faculty numbers are growing. So the research there has two themes. One is more theoretical, looking at studying physical processes, gravity, etc. with application to astrophysics. And the second is more observationally; observational based. And that involves taking data from a number of telescopes and also building telescopes as we all talk about. And that’s focused more on extragalactic astronomy and cosmology.

Jacinta: [00:15:57] So we’re here in Durban at the moment for the SARAO Bursary Conference 2019 – we’re in Durban. And this is where UKZN is, is that correct?

Kavi: [00:16:06] Yes, that’s right. So UKZN, has two campuses, well, actually three campuses in Durban.

There’s a medical school, the Howard college campus, which has mostly engineering and the arts and social sciences. And then there’s the Westville campus where most of the science and management science are, and there’s another campus in Pietermaritzburg. And the education campus in Pinetown.

Jacinta: [00:16:28] So I came up early for the conference for the weekend just to check out Durban a little bit.

I just ended up kind of staying by the beach cause there’s a nice beach. The water is a lot warmer than in Cape Town and it’s kind of very tropical, lots of green all the way down to the beach. Tell us a bit more about Durban for our international listeners.

Kavi: [00:16:45] Yeah. Durban is fantastic. The weather is great all year round. There have been many reviews that have awarded it in one of the best destinations, including CNN and, you know, other websites though. Yeah, the water is warm so you can swim all year round. It’s a great location for getting access to the wildlife parks when you’re two hours away or the mountains; the Drakensberg is also two hours away. So, and Durban itself is interesting. It’s quite multicultural. People from many parts of the world are here. And you know, green rolling hills and, the food is interesting; very diverse.

Jacinta: [00:17:22] Yeah. I was just about to say the food. There’s the famous Durban curry and bunny chow.

Kavi: [00:17:27] Yeah, and that’s, I guess, part of my legacy being of Indian origin. So it’s quite exciting, but there’s quite an interesting multicultural mix in Durban.

Jacinta: [00:17:38] And, what exactly is bunny chow? I’ve been meaning to ask someone local from Durban.

Kavi: [00:17:43] It’s a, basically a hollowed out, a fraction or quarter or half of a loaf of bread, where the bread is not sliced and then it’s followed with the spicy curry.

Jacinta: [00:17:54] All right. Back to science. What research do you do in particular?

Kavi: [00:17:58] So my primary research interest is in cosmology. I’ve worked on the Cosmic Microwave Background or still work on in that area. And more recently I’ve moved into working on cosmology from using radio observations, generally trying to understand what the universe is made of – these mysterious components of dark matter and dark energy and just how galaxies form and evolve.

Jacinta: [00:18:24] What is the difference between astronomy and cosmology?

Kavi: [00:18:27] I guess maybe just terminology. Astronomy is interested in probably a wider variety of phenomena in the universe, and one would say it incorporates cosmology because cosmology is the study of the universe on the largest scales, including the large scale structure that we see; the Cosmic Microwave Background and a variety of other probes. Astronomy extends to studying stars, planets, galaxies. So one could say that astronomy covers scales that are much smaller than we study in cosmology.

Jacinta: [00:19:03] Right. And so as part of studying this cosmology, is it correct to say that you are helping in the development of something called the HIRAX telescope?

Kavi: [00:19:12] Yes. As I alluded to earlier, HIRAX is a project we are driving here out of UKZN and has a number of partners in South Africa and international partners. The goal is to build a radio interferometer array so that’s a collection of roughly a thousand dishes that are six meters in diameter. And unlike MeerKAT or other radio interferometers, the HIRAX will be a very compact array rather than the dishes being spread out.

And the idea there is that you have a lot of sensitivity to large scales, you know, which you need to map out the large scale structure in cosmology.

Jacinta: [00:19:51] First of all, tell us about the name HIRAX.

Kavi: [00:19:54] So the name HIRAX – it’s an acronym for the Hydrogen Intensity mapping and Real-time Analysis eXperiment.

It was cleverly devised because it’s the Latin name is Hyrax, spelled with a Y, not an I, refers to the rock dassie, which is a resident of the crew, like the MeerKAT is. And so HIRAX will be located in the Karoo site.

Jacinta: [00:20:20] So Hyrax is a little animal.

Kavi: [00:20:22] Yes. Actually a related, its closest relative is the elephant.

Jacinta: [00:20:26] Oh really? But it’s a tiny little animal, isn’t it?

Kavi: [00:20:29] One would think that it has relatives, which are more furry.

Jacinta: [00:20:32] So you’ve said that this is a thousand dishes in the Karoo near the SKA site?

Kavi: [00:20:37] Yes. It’s about 15 to 20 kilometers and currently we have actually funding up to 256 dishes, but we’re planning to expand to a thousand dishes.

Jacinta: [00:20:48] How is it different to the SKA?

Kavi: [00:20:51] The SKA has different scientific applications. Since we’re interested in cosmology in particular, we are trying to map out the hydrogen in the universe, but not on scales of the galaxy, but on much larger scales. We’re looking for a signal that’s a on scale a hundred times larger than the typical separation between galaxies. So to get sensitivity to very large scales, we need to have a very compact array. Conversely, if you want to discover things on very small scales, you have very long baselines. So you put your dishes far apart. And that’s what the SKA and MeerKAT are aiming to do.

Jacinta: [00:21:34] Right, so MeerKAT and the SKA are going to excel in sort of high resolution stuff, where you’re looking at smaller scales, smaller objects, whereas HIRAX is just to see huge large scale stuff. Is that correct?

Kavi: [00:21:47] Yes. That’s right, the volume that HIRAX will map out in the universe will be significantly more than many of the surveys that are will be undertaken by MeerKAT or the SKA.

Jacinta: [00:21:58] All right, and what are the main science goals of HIRAX?

Kavi: [00:22:01] There are two leading science goals. The primary one is, of course, dark energy, and the idea is to use the distribution of hydrogen in the universe on the very largest scales to map out a feature called the baryon acoustic peak. And that’s a characteristic scale.

As I mentioned, it’s quite large compared to the size of galaxies; 150 megaparsec so over around about 450 million light years. To do that, we need to map out a large volume in the universe. Once we measure the baryon acoustic feature, that gives us a unique lens scale, which we can then track over time because we measure the hydrogen at different frequencies and with that lens scale, we can then set a constraint on dark energy.

Jacinta: [00:22:51] So this is essentially a big telescope to study dark energy.

Kavi: [00:22:55] Yes, that’s right. Yeah. That’s its primary goal because we have a compact array, another important application of the telescope will be to discover transient phenomena and in particular fast radio bursts, which are a very hot topic at the moment, and pulsars,

Jacinta: [00:23:11] Okay, so what’s a transient and what’s a fast radio burst.

Kavi: [00:23:14] So a transient is an object in the universe that appears for a very short time. Fast radio bursts, for example, are very bright flashes in the radio sky – as bright as some of the other objects in the radio sky, and they only last for a very short duration, maybe a millisecond. Until recently, we’ve only had a handful of detections of these fast radio bursts, mainly because you need to cover a large area of sky and you need a broadband to detect these objects. Recently, a telescope like CHIME have changed that and are we now detecting hundreds of fast radio bursts. So HIRAX will be well positioned to detect lots of fast radio bursts in the Southern sky because it has a large collecting area and it has a large area.it surveys on the sky.

Jacinta: [00:24:05] And there any theories as to what could possibly be causing fast radio bursts?

Kavi: [00:24:11] Yes, there’s many theories out there. In fact, at one point there were more theories than they were actual detections of fast radio bursts. It’s pointing to some energetic event in the universe.

Probably the collision of, or the merger of, two massive stars is one theory. There’s a vast number of models out there, and collecting more data will help us to narrow down the range of models that we see.

Jacinta: [00:24:38] So HIRAX will hopefully help us figure out what is causing these things, right?

Kavi: [00:24:42] Yeah. And I think a key advance that we will make with HIRAX, which are the projects are also attempting, is, to try to localize these objects. Currently, it’s difficult to simultaneously survey a large area on the sky, and then have good angular resolution to pinpoint where they’re coming from. So typically, the localization of these FRBs, in the region where they’re detected, could be hundreds of galaxies.

So what HIRAX is hoping or is planning to do, is to have very long baselines, which would give us higher resolution. So we plan to build a small outrigger stations of about eight dishes. And place these working together with partners in other African countries at remote sites in these partner countries, and then do long baseline interferometry with these signals that will allow us to detect these FRBs.  And simultaneously localize them to within the galaxy, not just in a particular galaxy, but within a spiral arm in the galaxy.

Jacinta: [00:25:50] Okay, so you have HIRAX, which is a lot of dishes close together so that you can see large scale things, but also you want some telescopes associated with HIRAX, much, much further away from this compact central region so that you can do very long baseline interferometry, as you’ve said. And so therefore, if we can also see smaller details, therefore you can localize – so find out where the burst is coming from. So, which of these partner countries throughout Africa will potentially have some of these outrigger stations of telescopes?

Kavi: [00:26:21] We’re in discussion with a number of interested partners. Currently the most advanced partners are Rwanda and Botswana. We’re also in discussion where people from Namibia, Mauritius and potentially Mozambique and Kenya – but those are less advanced. So, in addition to the African partner companies, we have a HIRAX prototype at the Hartbeestboek Radio Observatory just outside of Johannesburg – that’ll also serve as another outrigger station. So we plan to start off with two or three outrigger stations before we expand to other partner countries. These stations are relatively easy to deploy because they just comprise eight dishes.

Jacinta: [00:27:06] So this has the potential to be quite a pan-African telescope.

Kavi: [00:27:10] Yes. And we’re hoping that we can contribute just a little in growing the interest in astronomy around the continent and in particular radio astronomy. These arrays are fairly easy to get up and running, and they would, they make excellent instruments for students and researchers to get their hands dirty.

Jacinta: [00:27:31] Yeah, exactly. There’s nothing like actually being at the telescope for the dish to boost your interest and your learning. Now, I wanted to get back to dark energy because we very briefly skipped over that, but it’s so interesting. Okay. Let’s just go through what is dark energy and why don’t we know what it is yet?

Kavi: [00:27:47] So dark energy is this mysterious form of energy, a component in the universe, which causes the universe to actually accelerate in its expansion. So if we had the regular matter, like the stuff that we’re made of and that we see around us, we would expect the universe to stop or slow down in its expansion, because the matter is putting it back.

However, a dark energy has a negative pressure and that’s almost like a repulsive gravity, and therefore causes the universe not to slow down in its expansion, but actually just speed up. So you may say negative pressure. That’s weird. And it is weird. It’s a strange stuff that we’re talking about.

The closest thing, and probably the best theory for dark energy at the moment is something called the cosmological constant, which Einstein proposed. Giving it a name doesn’t mean we know what it is. People think that it’s some form of the energy of the vacuum. So in the absence of all matter, this would be the only energy present.

But the theoretical predictions for this vacuum energy differ vastly by many orders of magnitude from what we observe for the value of the energy today.

Jacinta: [00:29:03] How is HIRAX going to help us figure out what it is?

Kavi: [00:29:06] So HIRAX will, as I mentioned, measure the large scale distribution of hydrogen in the universe that hydrogen chases the large scale structure.

And that structure has imprinted in it, something called the baryon acoustic peak, which is a unique lens scale that we can predict very accurately. So we will measure this lens scale with a percent level measurements and we will not just do that at one instant in time, but we will do that over a wide range of time.

So HIRAX will observe from about 11 billion years ago. To about 7 billion years ago. And that’s an important epoch because that is when dark energy was becoming important in the universe and was beginning – or starting after that period is, when it became dominant in the universe. So we will be able to measure how the universe – this lens scale – changes over time, over a wide range of time. And that will tell us what the behavior or properties are of dark energy.

Jacinta: [00:30:09] Okay, so it’s at least going to help us to understand more about the properties of dark energy and maybe that will lead us towards what it actually is.

Kavi: [00:30:19] Yes in particular, I mentioned the cosmological constant, that has a fixed equation of state, which is the ratio of the pressure to the density and its value is minus one, so it has negative pressure.

What we are hoping to do is to determine if they are deviations from that equation of state. So if the ratio is not minus one, that would point to very interesting new physics.

Jacinta: [00:30:44] Oh, lots of mysteries that HIRAX will help us solve. And when can we expect this telescope to be ready?

Kavi: [00:30:49] So at the moment, we are putting out a tender or bid for dishes for the telescope.

So that’ll be early next year. And we hope to by the end of having testing these dishes to install them at the Karoo site in South Africa.

Jacinta: [00:31:07] Great. And do you have any final messages for listeners?

Kavi: [00:31:11] Yeah. I’d like to direct the message to the young people out there who are fascinated by science and astronomy.

Certainly pursue your passion and it’s a hard journey, but don’t give up and you’ll be rewarded for it.

Jacinta: [00:31:25] Wonderful. And if people want to find out more about you and your research group and HIRAX, where can they go?

Kavi: [00:31:31] And you can look up the astrophysics and cosmology research unit.

ACRU , which is at UKZN, and we have a website. HIRAX also has a website which is hosted at UKZN. so it’s H-I -R-A-X-dot-U-K-Z-N-dot-ac-dot-za.

Jacinta: [00:31:47] And can we find you anywhere on social media?

Kavi: [00:31:49] We have an active social media presence through our research unit. So certainly if you look for ACRU on Twitter, Facebook, you could catch up with me indirectly through those social media platforms.

Jacinta: [00:32:04] Thank you so much for speaking with us today, Kavi, it’s great, to catch up with you as always.

Kavi: [00:32:08] Thanks very much Jacinta, and I hope you have a good day.

… music playing…

Jacinta: [00:32:20] So a lot of great science there. I do also have to admit, Dan, that I didn’t taste bunny chow in Durban because I can’t really handle a lot of spice.

Dan: [00:32:30] Well, you missed out.  I don’t know if the listeners know: I grew up in KZN. So I grew up on bunny chow – it’s delicious. I mean, it’s very high on the carbs because you’re having a lamb and potato stew inside half a loaf of bread. Yeah.

Jacinta: [00:32:51] You wouldn’t want to go back to work after that. You’d be very, very drowsy. Food coma.

Dan: [00:32:58] Yeah. You know, delicious. I could do one right now. I’m sure

Jacinta: [00:33:02] I tried one in Cape Town once, but I think it was like a really watered down Cape Town version ‘cause it wasn’t very spicy.

I want to know what dark energy is. Getting back to science again.

Dan: [00:33:15] I don’t we all, and I think that that’s one of the nice things. This is another great project, which is getting both in South Africa, and maybe we’ll answer some of those questions or at least get closer to answering those sorts of questions.

It’s great. We hear a lot about MeeerKAT. We hear about SALT and some of the other big projects that are going on, but there’s a lot of these other projects happening too. We’re exploring a lot of different realms of science all at the same time and it’s exciting.

Jacinta: [00:33:45] Yeah, definitely lots of different things.

It was a bit refreshing to talk about radio astronomy, that’s not MeerKAT, even though I love it. There are other instruments out there. Well, all of that talk about bunny chow. I kind of want to go and get some lunch now.

Dan: [00:34:00] Yeah, me too. All right. Thanks for joining us again, and we hope you’ll join us on the next episode of The Cosmic Savannah

Jacinta: [00:34:07] In the meantime, you can visit our website, thecosmicsavannah.com where we’ll have the transcript of this episode and related links. You can also follow us on Twitter, Facebook, and Instagram @cosmicsavannah, that Savannah spelt, S-A-V-A-N-N-A-H. Thanks to Sumari Hattingh, Brandon Engelbrecht, Lynette Delhaize, and Thabisa Fikelepi for social media and transcription assistance.

Also to Mark Allnut from music production, Janus Brink for the Astrophotography and Lana Ceraj for graphic design. 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 and we’ll speak to you next time on the Cosmic Savannah.

…music playing…

Dan: [00:35:13] All right. Thanks for joining us again, and we hope you’ll join us. Argh!

This is why we have a script

Jacinta: [00:35:25] so that you can not read it!