Episode 31: Cosmic Beasts and Where to Find Them

with Dr Jacinta Delhaize

Happy 2021! We’re looking forward to another exciting year of astronomy!

This year we get off with a bang as our very own Jacinta has a new paper out and takes her turn in the hot seat to tell us all about it!

Along with her colleagues, she has been part of the discovery of two giant radio galaxies using South Africa’s powerful MeerKAT telescope.

These galaxies are amongst the largest single objects in the Universe and are thought to be quite rare. The fact that MeerKAT detected two of these monsters in a relatively small patch of the sky suggests that giant radio galaxies may actually be much more common than previously thought.

Above: The two giant radio galaxies found with the MeerKAT telescope. In the background is the sky as seen in optical light. Overlaid in red is the radio light from the enormous radio galaxies, as seen by MeerKAT.
Credit: I. Heywood (Oxford/Rhodes/SARAO).
Above: Centaurus A is a famous example of a relatively nearby radio galaxy. Inside the galaxy is a supermassive black hole which is generatingthe large jets which can be seen emerging perpendicular to the disc of the galaxy. Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray).
Above: Part of the MIGHTEE radio map of the sky. A zoom in of each giant radio galaxy is shown in greyscale. The purple line traces around the radio emission from the giants. Image credit: I. Heywood (Oxford/Rhodes/SARAO)

This week’s guest

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Featured Image:

The two giant radio galaxies found with the MeerKAT telescope. In the background is the sky as seen in optical light. Overlaid in red is the radio light from the enormous radio galaxies, as seen by MeerKAT. Left: MGTC J095959.63+024608.6. Right: MGTC J100016.84+015133.0. Credit: I. Heywood (Oxford/Rhodes/SARAO).


Transcript by Lynette Delhaize.


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

Jacinta: [00:00:08] 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: [00:00:17] 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.

Dan: [00:00:34] Welcome to episode 31. Happy New Year, everyone.

Jacinta: [00:00:38] Yeah, happy New Year!

Dan: [00:00:39] We are once again recording over zoom. We are socially distanced and confined pretty much to our homes. So apologies for any sound issues or slight delay or. Jacinta and I talking over each other.

Jacinta: [00:00:55] We’ve got a fancy new setup now where I’ve got a home recording USB microphone set up. Thanks mum! It was my Christmas present. And Dan has our usual recorder in his house.

Dan: [00:01:07] Well, if you’re listening to it, then it’s worked. Yeah. All right. So 2021 from an astronomical point of view…

Jacinta: [00:01:13] there’s a new rover landing on Mars this year, right?

Dan: [00:01:16] Yeah. The Perseverance Rover will be landing this year, which is always exciting. We spoke about it a little bit last year. That’s super cool. They’re a few months away, I think. The launch of the James Webb Space Telescope should finally be happening this year.

Jacinta: [00:01:30] Oh I can’t wait!

Dan: [00:01:32] I’m not holding my breath.

Yeah. It’s gone through numerous delays over the years, so we’ll see. That’ll be very, very exciting and very, very stressful launching something like this.

I’ll be watching that launch with bated breath. In terms of celestial events observable from Earth, there’s nothing major. There’s a small eclipse visible from Cape Town, the 4th of December.

Jacinta: [00:01:57] Luna or solar?

Dan: [00:01:59] Solar, a small solar eclipse. But it’s a very small percentage visible just from Cape Town, not the rest of South Africa and actually it’s centered over Antarctica, which is quite exciting. If you can manage to get there. I’m sure we’ll get a couple of good photos out of that one. So, yeah, I guess we should get going with today’s episode.

Jacinta: [00:02:18] Yes.

Dan: [00:02:19] And what do we have in store today?

Jacinta: [00:02:21] Who are we interviewing today?

Dan: [00:02:24] Well, it’s the moment you’ve all been waiting for and I’ve been waiting for for some time. Jacinta’s long awaited paper is finally out. And so we can talk about it. I guess there’s an embargo until today, until it comes out and you can tell us all about it. So Jacinta… welcome to The Cosmic Savannah!

Jacinta: [00:02:47] No, you’re meant to call me Dr. Delhaize. Remember? Cause I’m the guest.

Dan: [00:02:52] Well, wait, let me do it…The Esteemed Dr. Jacinta Delhaize, welcome to The Cosmic Savannah.

Jacinta: [00:03:00] Yes well, hi, nice to be here. I’m actually quite nervous. I guess this is what it feels like to be a guest on our show.

Dan: [00:03:07] Just relax. It’s a conversation. That’s what we tell our guests, right?

Jacinta: [00:03:11] Ok, chilling. Well, I guess, well, you have to ask the questions, don’t you?

Dan: [00:03:16] Yeah. I have to ask the questions this time.

Let’s get into it. Your paper, you have discovered well, you and your team have discovered two giant radio galaxies using the MeerKAT telescope. And these galaxies are amongst the largest single object in the universe  and obviously quite rare.

Before we get into the discovery and what exactly it all means, I think we should do a sort of introduction to radio astronomy. Talk a little bit about what it is and how it differs from optical astronomy. What exactly are we looking at and how are we doing it?

Jacinta: [00:03:52] Sure. Okay, so astronomy uses the whole electromagnetic spectrum, some telescopes can detect optical light, which is the same light as we can see with our eyes.

So they’re just basically huge eyes, but then we can also have different telescopes that can see ultraviolet light, infrared, the whole range of wavelengths down to the lowest frequencies or the longest wavelengths, which are the radio. And radio telescopes kind of look like big satellite dishes. There are several around the world and a new one in South Africa is called MeerKAT.

That’s in the Karoo and it comprises of 64 individual dishes and combined together it’s called an interferometer, which is pretty much one of the best in the world, if not the best at what it does. This is a pretty new telescope. It was launched… What? June 2018?

Dan: [00:04:47] That’s correct.

Jacinta: [00:04:47] And since is starting to make some pretty cool discoveries, including this one that we’ve made.

Dan: [00:04:55] Yeah. So we’re basically looking at radio waves which are coming in. As you said, MeerKAT’s a 64 dish array. And the reason we do an array is because in order to detect these very long wavelengths, we’d ideally like to have a huge square kilometer big dish. But that’s kind of unfeasible. So instead we build these arrays and then combine the signals to simulate a much bigger telescope.

That’s interferometry.

Jacinta: [00:05:26] Well, that’s getting towards the SKA which MeerKAT is the precursor of, but yes, that’s what we’re heading towards.

Dan: [00:05:32] I don’t know what the combined collecting area of MeerKAT is, but it’s pretty big. 64 dishes which are each kind of 13 meters big.  You’ve spoken a little bit about MeerKAT launched in 2018.

What makes MeerKAT so special? Why is it so powerful and what are the technological advancements which we’ve seen from MeerKAT?

Jacinta: [00:05:52] The one thing about MeerKAT in particular is that it’s very, very sensitive, so it can pick up very, very faint light or light from very large distances. And this is because what we call the receivers, the part that received the light, the radio waves, these are cryogenically cooled and they perform even better than they were designed for. So this thing is really, really sensitive.

The other really good thing about MeerKAT is that because there are so many of these individual dishes, 64 of them, we can spread them out. Some close together, some really far apart. And the greater the number of different distances between telescopes the more completely you can see the sky.

So if you have telescopes that are closer together, if you have dishes that are closer together, you’re going to be able to see things on the sky that are much larger scale. And if you have telescopes that are further apart, you’re going to be able to see things on a smaller scale. And so because we have this whole range, we can see small features in the emission from the galaxies or from whatever we’re looking at. And we can see large features.

And the way this has helped to make the discovery that we’ve published today is that this makes the MeerKAT telescope really sensitive to what we call “diffuse emission”. This is kind of like large scale fuzzy stuff. That’s very, very faint and distributed over large patch of sky.

Dan: [00:07:17] Okay. So you mentioned your discovery. Let’s get into it. You’ve discovered two giant radio galaxies. Firstly, what is a radio galaxy and how does it sort of differ from a regular galaxy?

Jacinta: [00:07:29] Okay. So galaxies, as we know are big collections of stars and gas and dust and dark matter and such, and you might have what we call a normal galaxy or star forming galaxy, which is just chilling out and it’s forming stars and converting its gas into stars. And those stars go supernova and then etc.

But some galaxies are called active galactic nuclei. Most galaxies have a supermassive black hole in their center, and this black hole becomes active when you have stuff falling into the black hole. So whether that be gas or dust coming from the galaxy or coming from the intergalactic medium, which is the stuff between galaxies.

So this is trickling in into the black hole and it’s heating up a lot as it does so. Then we call this black hole active. We call this whole galaxy an AGN, an active galactic nucleus. This activity is emitting a huge amount of very high energy light. It can be emitted across the entire electromagnetic spectrum all the way from the gamma rays down to the radio.

And when you have a lot of radio emission coming from this region, it’s called a radio galaxy. And often this is in the form of two kind of beams coming usually above and below the plane of the galaxy itself. And we call these jets. There are relativistic particles. These are highly charged particles like electrons, which are traveling close to the speed of light and they are interacting with the magnetic field around the black hole.

These are spiraling in the magnetic field and emitting what we call synchrotron radiation, which is predominantly admitted in the radio. Right? So we have these huge beams of radio emission coming from above and below the black hole in these huge jets. And this is what a radio galaxy is.

Dan: [00:09:20] We really got you excited there didn’t we? Okay. It’s a lot to take in. So essentially a radio galaxy’s got the supermassive black hole at the center, which when it’s feeding, essentially taking in gas sometimes excites that gas and pushes out large jets of high energy particles, which we can detect in the radio wavelengths.

Jacinta: [00:09:48] Exactly.

Dan: [00:09:49] Okay. Got it. So what is a giant radio galaxy then?

Jacinta: [00:09:55] These jets of light, of which we will put a picture on the website for this episode. These huge radio jets, we think that they grow. So they start out small and then as the galaxy ages, they get bigger and bigger and bigger and bigger pushing further and further outwards from the galaxy.

They can come in a whole range of sizes. And the giant radio galaxies these are ones that are bigger than 700 kiloparsecs, which is around 22 times the size of our own galaxy, the Milky Way. So these are really truly enormous systems and these particular ones, we call giant radio galaxies.

They’re actually fairly rare. We’ve found hundreds of thousands, even millions of radio galaxies of all different sizes, but only about 800 or so of them are classified as giants. So relatively rare.

Dan: [00:10:44] Are they giant in mass or just giant in size?

Jacinta: [00:10:47] Giant in size. So we measured the size as the distance between the end of one radio jet and the end of the other. So the full extent.

Dan: [00:10:54] So they don’t necessarily have more stars in them. They’re just kind of more diffuse things.

Jacinta: [00:10:59] Yeah, exactly. So their end to end size is really enormous. The galaxy at the center, it can vary in what it looks like, but often it will be hosted by a galaxy that is what we call a red and dead elliptical.

So it’s an elliptical galaxy, which has very little gas in it and therefore it’s not forming many stars. So the stars that are inside it are kind of turning red because stars turn red as they age and without new stars forming that are blue, this whole galaxy looks red.

Dan: [00:11:26] Is that why these sort of large galaxies haven’t been detected before? I mean, is it because their stars aren’t quite so bright and they’re more diffuse?

Jacinta: [00:11:35] No. So what we call the “host” galaxy, the galaxy that is hosting the black hole and emitting the radio jets. That’s actually fairly bright. I mean, we can see it very clearly in the optical images, but what hasn’t been detected before is the radio emission.

The particular galaxies that we have found with MeerKAT, they have been found before in the radio wavelengths. So actually that was part of the work that I did in my previous postdoctoral research position in Croatia where we studied the same patch of sky with a telescope in New Mexico called the Very Large Array. And the benefit of the Very Large Array is that it has very, very good angular resolution.

That means that it can see details very, very clearly and very, very small details. And in that data, you can see these galaxies, you can see the radio jets, but only the inner parts of them, the very, very inner parts. So in that data, these look like radio galaxies, but not giants, just kind of small ones. So we’d found  them before  and we’d found their elliptical host galaxies, but they just looked small. What we found in the new data is that not only do they have these little inner jets, they’ve got these huge, enormous outer jets, many, many, many times bigger than the previous ones that were found. And so that’s how we now know that these are giant radio galaxies.

And it’s because of the excellent MeerKAT sensitivity to diffuse emission, which I said at the start, the ability to detect large scale, very faint emission or light on the sky. That’s why we can now pick up the giant lobes of this galaxy. Whereas we couldn’t see it in other data from telescopes like the Very Large Array or from the Giant Meter-wave Radio Telescope in India, which has also looked at this particular patch of sky called COSMOS.

Dan: [00:13:25] All right so you haven’t discovered new galaxies. You’ve just discovered a larger radio emission, a more diffuse radio emission than has been discovered before from these galaxies. And they’re not necessarily giant galaxies, although they are big, but they’re giant in the radio.

Jacinta: [00:13:42] Well, it depends what you mean by galaxy.

What do you mean by a giant galaxy? Classically that’s considered to be the size of the part of the galaxy that contains all the stars. But all of these radio jets, this plasma, this is also part of the galaxy.

Dan: [00:13:57] Ah touche.

Jacinta: [00:13:58] But we haven’t really considered that to be the size of galaxies before, because we couldn’t actually see it.

Dan: [00:14:03] Ah but then, I mean, you know, there could be this diffuse emission around all galaxies, but it’s just not getting lit up.

Jacinta: [00:14:10] Well, we’re looking with MeerKAT now, and we’re not finding that except for in a few examples such as these.

Dan: [00:14:16] Yeah. Then that leads me onto my next question. What does this mean for galaxy formation and evolution or our understanding of it?

Jacinta: [00:14:24] Okay. So, yeah, that’s a good question. There’s actually something else special about these galaxies and not only are they giants that hadn’t been identified as giants before, they’re also particularly special giants. We had a look at how these compare to other giant radio galaxies in size and what we call “luminosity” or “power”. By luminosity or power we mean kind of how bright the radio waves are, how much emission is coming from them. And they’re actually really quite faint. So we’ve found galaxies that are much larger and a bit fainter than most other giant radio galaxies that have been found. This means that they are quite unique objects and it probably means that there’s a lot more of them out there. There might be this extra population of giant radio galaxies out there that we haven’t seen before, simply because our telescopes couldn’t pick up this diffuse light, which MeerKAT can now see. This would actually match what we have predicted from models of how these radio galaxies evolve over time.

As I’ve said, we think that these radio jets, they start off small, so contained quite close to the stars, but then they grow outwards over time. If this is really why some galaxies become giants, then this would mean that we should see quite a lot more giant radio galaxies than we are actually seeing.

So it looks like they are there. We just hadn’t seen them before because of the limitations of our telescopes. And this is all information we need in order to understand how galaxies evolve or change over time, over cosmic time, since they were formed after the Big Bang till now. We need to understand all of these different physical processes that are going into them to understand the whole picture of galaxy formation and evolution.

Dan: [00:16:16] Yeah and you mentioned that, you know that there could be other giant radio galaxies like this, and we should be detecting them. These galaxies you detected, and you’re part of a survey called MIGHTEE, and presumably the MIGHTEE survey is going to carry on and is expected to detect many more of these. Can you just explain a little bit about MIGHTEE? What does it stand for firstly, and then what is its goal? What can we expect coming out from the survey in the next few years?

Jacinta: [00:16:46] MIGHTEE, that’s an acronym which I’ve just had to look up because I can never remember it.

It stands for the MeerKAT International Gigahertz Tiered Extragalactic Exploration survey. So mightee: M I G H T E E. And this is a galaxy evolution survey planned with MeerKAT and underway. So initially when MeerKAT was being planned  there were several large survey projects planned. So international astronomers got together and formed collaborations and decided what most of the time on MeerKAT was going to be spent doing. And they sent in proposals. And the plan for MIGHTEE was one of them.

This was to create a really large scale galaxy evolution survey. Now, what does that mean? It means that MeerKAT is looking at several large patches of sky. In total it’ll be about 20 square degrees. Now to give you an idea, the area of the full moon is about half a square degree. Fairly large patches of sky.

And their goal here is to pick up the radio light from many hundreds of thousands of galaxies. And in doing that, you can study for example, the hydrogen gas, the neutral gas within these galaxies, which is the raw fuel of star formation, which we have spoken about a few times previously on The Cosmic Savannah.

And you can also study what I mentioned earlier, the synchrotron emission. So that’s this special lightgenerated by these electrons moving really fast in the magnetic fields. Sort of weird other things like polarization, where the direction of the light, the angle of the light is changing, but we don’t need to go into all of those details.

There’s a lot of different components of this MIGHTEE survey, but it started off with Early Science observations or Pilot observations. So this is just to check whether everything’s going right. These are the first set of observations to see if the survey has been well-planned. So to do that, MIGHTEE looked at one patch of sky one square degrees in size. So about four full moons can fit into that region.

And we looked at a particular patch of sky called COSMOS, as I mentioned earlier, and this patch of sky has been looked at by many other different telescopes in the past, in the radio light, in the x-rays in ultraviolet, in the infrared. And so we have a lot of data to compare with.

That’s important because all of this extra types of data that can let us figure out how far away these galaxies are. And once we’ve done that, we can have a look at how much light we’re detecting from them. And we can figure out what the actual strength of the light is because of course if you’ve got a galaxy that is close to you, but a bit faint, it’s going to look the same brightness as a galaxy that is further away from you and quite bright.

One of the things that we found straightaway when we looked at this early science data and of the COSMOS field was we spotted these two huge extended objects. Which turned out to be these giant radio galaxies that I have published a paper on. And they really looked fantastic. We’ll post a picture on the website of a cutout from the radio map of the sky that MIGHTEE made. And you can see really clearly these big streaks, these fuzzy streaks across the sky. And those are these giant radio galaxies that we found. Now, this was really exciting because if there are only, let’s say about 800 giant radio galaxies known, and a lot of these have been found with the LOFAR telescope, which stands for the Low Frequency Array, which is sort of based in the Netherlands and Europe. With that telescope most of  these giant radio galaxies were found, and we looked at how they were distributed across the sky. And based on that, we really didn’t suspect to find even one giant radio galaxy in this tiny one square degree patch of sky that we looked at. The fact that we found two is incredible. The probability of finding two, based on what we know about the distribution on the sky of giant radio galaxies, is very, very, very small. Incredibly small.

So either we have been insanely lucky to find these, or there are many more giant radio galaxies than we previously knew. And so that’s how we came up with this very exciting conclusion that there may be many more than we knew before. And that we’re starting to find them now with surveys like MIGHTEE, that are able to detect this very faint diffuse emission because of how sensitive they are.

Dan: [00:21:10] That’s super cool. And how much of the sky is MIGHTEE going to look at and how long is it going to take and how many of these things can we expect?

Jacinta: [00:21:21] So it’s going to look at in total 20 square degrees. So for comparison, what I’m talking about was one square degrees. These early observations, which four full moons will fit into it.

So you times that by 20 that’s how big ultimately the field will be. It’ll take several hours. So the observations that we looked at of the COSMOS field, actually they took only about less than 24 hours. So it’s actually incredible how sensitive this MeerKAT telescope is because the same patch of sky with the Very Large Array we had to look at for 400 hours with the Very Large Array before we could get to the same level of sensitivity.

So it’s going to take quite a few more hours to finish the whole survey. But the thing is we have to share the telescope. So not all of the observations can be dedicated just to MIGHTEE. We have to share with other surveys.

Dan: [00:22:12] You’re not going to get 20 days straight up.

Jacinta: [00:22:14] No.

Dan: [00:22:15] It’s probably just as well otherwise you’d have a lot of work.

Jacinta: [00:22:19] Yeah. Right. Of course, this is definitely not just me doing it. This is an international team of several dozens of astronomers. This is led by Matt Jarvis at the University of Oxford and Russ Taylor at the University of Cape Town. And then there are many other people who work very, very hard on this, including Ian Heywood, who is the second author on my paper and many others.

So yeah, not just me.

Dan: [00:22:44] MeerKAT is a precursor to the Square Kilometer Array which we mentioned earlier, and that’s going to be coming in the next five or 10 years. Recently the SKA was ratified. There’s many, many partner countries involved, and I think the final signatures happened in December.

So it’s, it’s official now that the SKA is an international organization. There’s a treaty and construction can now start on the SKA. That’s obviously going to be even more sensitive than MeerKAT. What are you looking forward to from SKA in terms of this kind of research in this field?

Jacinta: [00:23:27] Yeah, that’s a good question.

So the SKA is just so incredibly exciting. Of course, it’s going to be built partly in South Africa and partly in Western Australia. Each of those two components of the SKA will detect slightly different frequencies of the radio light. And it’s going to be, I think, revolutionary for our understanding of galaxy evolution, our understanding of radio galaxies, and radio astronomy because it will combine the best qualities of all the different telescopes in the world.

So the best qualities of the Very Large Array, the VLA, the best qualities of MeerKAT and ASKAP in Australia. MeerKAT, as I’ve said, is very good at detecting diffuse emission. So it’s very good at detecting large scale things.

And it’s very, very sensitive. It has good angular resolution, meaning it can see smaller details, but not as good as the VLA. So the VLA has really good angular resolution. The SKA will have both will have everything, right? So it’s going to be very, very sensitive, even more sensitive than MeerKAT by many times.

And it’s going to have really amazing angular resolution. So can see very, very small details. If you can see details that are very, very small and very, very faint, you can see things that are very far away and everything in between there. And of course, as you’re looking further and further away, you’re looking back in time because of the amount of time it takes for light to travel to the Earth.

So we’re going to have this amazing new crisp view of the Universe as seen in the radio light. And I can’t wait to see what will happen. And hopefully not only will MeerKAT detect many more of these giant radio galaxies. So hopefully we’re even going to find more in MIGHTEE in the other fields that haven’t been looked at yet.

But then with the SKA who knows what we’ll find? Maybe we’ll find extra giant radio galaxies, or I dunno, what would we call them? Uh, humongous giant radio galaxy, or something like that.

Dan: [00:25:22] We’ve got a few years to try and come up with a good name.

Jacinta: [00:25:24] Yeah. I clearly, I’m not very good at naming, so we’ll have to do a workshop on that.

Dan: [00:25:31] Okay. Well, Dr. Delhaize, thank you very much for joining us on The Cosmic Savannah.

Jacinta: [00:25:37] It was a pleasure to be here, Dan. Thanks. It’s so weird!

Dan: [00:25:42] Congratulations on your paper. Well done for getting it out. That’s quite an achievement. It’s super exciting.

Jacinta: [00:25:48] Thank you. It’s been a long haul.

Dan: [00:25:51] Maybe we can just explain to the listeners, I mean, what does it mean to get a paper?

It’s not like an article in the newspaper, right?

Jacinta: [00:25:57] No. Yeah. And why it takes so long as well.

So a scientific publication or a paper is the goal of your work as an academic. It’s to make a discovery or a finding and then publish it. So tell other people. And the whole process can take several years. It can be very quick if you are very, very, very lucky and very efficient, but usually it takes several years. The way that it works for me, because I’m an observational astronomer is I wait for the telescope to take the data and I wait for team members to process the data. Because it doesn’t come out of the telescope looking like a nice, pretty map. You have to do a lot of complicated things to turn it into an image of the sky. And then you kind of look at that data and you find something interesting and then you analyze it. So this is usually using a lot of coding and a lot of programming.

And doing the analysis. So applying knowledge of astrophysics. So this is where your knowledge of physics and maths comes in. You read a lot of other people’s papers. You can’t just read textbooks on the topic to understand the research the field that you’re in because the textbooks aren’t updated quickly enough to be cutting edge because papers are coming out every single day with newer and newer and newer research.

And you have to be really up to date on the very latest stuff in this research field that you’re working on. So you have to go and read all of these papers and understand what the cutting edge is. And then you have to start to write your paper. You write up your discoveries and what you found, you compare it to what other people have published in the literature before.

And then you finish writing this paper. So mine is about 15 pages, but you can have shorter papers. You can have longer papers. That’s  about an average size, I’d say about 15 pages with very, very small font and double columns and figures and pictures in it and everything. And then you submit it to a journal. And a journal is a…how would you describe a journal, Dan? I’ve never really been sure how to describe them.

Dan: [00:28:01] It’s a publication, you know. It’s like a newspaper, except it’s a formal publication, which comes out generally once a month from an organization which collects and processes these papers. So they keep a record of all of the papers, which get published.

Jacinta: [00:28:21] And it used to actually be published in an actual journal, an actual magazine sort of thing, which was sent out to all of the institutes.

But now of course, most of it’s just online because we all got access to the internet. We can just download all of the papers. We can save paper, save some trees in the process. You can choose which journal. There are several that you’d want to submit to. Usually you try and submit to a journal that has a what we call a high impact factor, so it’s got a really good reputation.

You submit it to this journal. I submitted it to the Monthly Notices of the Royal Astronomical Society. And then they do this important process called a peer review. They send your paper to somebody else who is an expert in the same field, but who was not an author on your paper.

And they have to read through it and they have to make suggestions and say, okay, yes, this paper looks like it’s scientifically rigorous. This is really well done. All of the analysis is correct. Or they make suggestions for changes. They say, oh look, you’ve actually forgotten to factor in this. Or then they might make some small changes, they might suggest some big changes. And then you get it back and you have a chance to change things. And then you can submit it back to the journal and then it might go through that process again, or it might be accepted.

My paper was accepted in, I think it was December of 2020. And then you have to do some things like you have to make sure it’s all type set to the nice format of the journal and you wait for that to happen.

And then finally it gets published. And often you also put it on the public archive, which is where everybody can access it because some of these journals are closed access. So you actually have to have a subscription to access them. But we obviously want everybody in the world to be able to access science and what we publish. So that’s why we also publish a version of it in the public access area. And that’s the process from start to finish.

Dan: [00:30:09] Thank you.  I should point out that that practice of publishing things on what’s called the arXiv, which is a freely available archive of all of the papers, is kind of unique to astronomy.

Jacinta: [00:30:22] Is it?

Dan: [00:30:23] Yeah. Most other sciences and especially medical research and things are behind a paywall. So you can’t access these journals without paying. And that slows the whole process down quite a lot, actually. Whereas in astronomy, often people post on the arXiv things which have been submitted, but actually haven’t been peer reviewed yet. Just to give people an indication of what’s going on and what’s coming. 

Particularly if you’re experienced and confident in your work. Are you’re confident it’s going to get published without many changes. You stick it on the arXiv and people can read it that day. You can publish it one day and it’s out there the next. So it’s a really good way for astronomy to move forward quickly and for these discoveries to be shared.

Jacinta: [00:31:08] Yeah, we don’t have to wait for months and months for the journals to publish it.

Dan: [00:31:13] You don’t actually I have to wait for these articles to be formally published. You can read them almost instantly.

And then the last step of the publishing process, which you didn’t mention is once it’s out there, then you start again.

Jacinta: [00:31:27] Well, yeah, I’m avoiding that part.

Dan: [00:31:30] So take a deep breath and do it all again.

Jacinta: [00:31:36] That’s right. I mean, I guess I could mention if you want the next step.

Dan: [00:31:40] What’s coming next? You must have one in the pipeline.

Jacinta: [00:31:43] My bosses are listening to this. So yes, I’ve been working very hard. Yeah. So I guess you usually have several projects kind of going on at the same time that you’re working on. But I’ve got several ideas of where to go from here with regards to these giant radio galaxies. I’ve put in a proposal to observe them again with MeerKAT, but at a different frequency, at a lower frequency.

And this is going to give us information about the actual age of the electrons in different parts of the jets. So what we think is that we’re going to find that they’re very young towards the center and very old towards the outside. But we are actually trying to find out whether these galaxies are restarted, meaning that the black hole kind of switched off for a while and stopped forming jets.

The old jets kind of kept expanding outwards and then suddenly it switched on again so that you’ve got these new little inner jets and this would indicate restarted activity. Which means that the supply of gas or whatever is falling into black hole, stopped for a while, and then started again, this is going to give us a lot more clues about what’s going on.

So I’m waiting to hear whether or not my observing proposal was successful. So I submitted this application to MeerKAT. Then there’s  a time allocation committee who are going to assess it. Lots of people are applying for time, so it’s very competitive. So I may not get this time,  this round, but there’ll be another opportunity later to try again.

This is one idea, but another thing I can do is go and look through the rest of the MIGHTEE data. Some of it has been taken in other areas of the sky as I mentioned, it’ll be 20 square degrees in full. And so some of that data already exists. So I can go and check that out. Go galaxy hunting, and see if I can spot some more giant radio galaxies.

Dan: [00:33:23] Awesome.

Jacinta: [00:33:24] And they should be there, right? If we’re right that there are two of these in each square degree of the sky, we should be able to find, I mean, there should be 40 in the entire MIGHTEE region. So fingers crossed we find some.

Dan: [00:33:36] I bet you there aren’t. And then you’re going to have to rethink the whole thing again.

Jacinta: [00:33:40] No, Dan don’t say that! But actually that could be more interesting to be like, what on Earth is going on in this particular part of the sky?

Dan: [00:33:49] Yeah. That’s the fun. You never really know what you’re going to get.

Jacinta: [00:33:52] Yeah, exactly. And so that’s a risk, right? You might start a project and it could go nowhere because you don’t know what the answer is.

That’s the point of science is that you’re doing something that no one else has done before, but it could also be a really cool discovery. 

Dan: [00:34:05] Great so I think that’s it for today.

Jacinta: [00:34:08] Yeah. So thank you for having me as a guest. It was a weird experience. You could hear how nervous I was.

Dan: [00:34:16] That was great. I mean, we’ve been wanting to talk about your research for a while and you’ve kind of been holding it close to your chest because there is something about that.

This research and endeavor, you don’t want to get scooped either. You don’t want somebody else to see your idea before you’ve published it and then publish it themselves. Because that does happen too. So you do kind of hold these things a little bit close to your chest. Mostly it’s a kind of nice environment, but it’s rare.

Jacinta: [00:34:44] Mostly people are really nice and cool about that, but it can happen.

But, anyway, I wanted to time this with the release of the official publication of the article, of the paper, and also the press release. I wrote a little press release and I’ve sent it out to various places. And so if anyone wants to contact me to talk about it, you can.

Dan: [00:35:01] Yeah. Let’s, let’s hope it gets picked up.  You know, it’s a pretty cool discovery and well done.

Jacinta: [00:35:07] Thank you.

Dan: [00:35:08] And thank you very much for listening. We hope you’ll join us again for the next episode of The Cosmic Savannah.

Jacinta: [00:35:13] You can visit our website, thecosmicsavannah.com, where we’ll have the transcript, links to other stuff related to today’s episode.

And you can follow us on Twitter, Facebook, and Instagram @cosmicsavannah that’s Savannah spelled S a v a n n a h.

Dan: [00:35:29] Special thanks today to Dr.  Jacinta Delhaize for speaking with us.

Jacinta: [00:35:34] Thanks to our social media manager Sumari Hattingh, and all The Cosmic Savannah volunteers. Also to Mark Allnut for music production, Janas Brink and Michal Lyzcek for photography and Lana Ceraj for graphic design.

Dan: [00:35:47] We gratefully acknowledged 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.

Jacinta: [00:35:57] You can subscribe on Apple podcasts, Spotify, or wherever you get your podcasts. And if you’d like to help us out, please do rate and review us and recommended us to a friend.

We’d really appreciate it.

Dan: [00:36:07] And we’ll speak to you next time on The Cosmic Savannah.

Jacinta: [00:36:19] This is really good practice for me. It’s hilarious how, like, ah, I’m nervous and I’m stumbling and it’ll be good for like radio interviews to practice this stuff.


Bonus: Rerun – Event Horizon Telescope

with Prof Roger Deane and Dr Rodhri Evans

The Cosmic Savannah team are off on summer holidays, but Jacinta drops by to wish you all happy holidays and introduce you to this re-run of Episode 5 from Season 1.

This episode is about black holes, in celebration of the 2020 Nobel Prize in Physics being awarded to 3 astrophysicists for their black hole-related research.

Roger and Rodhri tell us about the Event Horizon Telescope, used to make the first ever image of a black hole, and the African Millimetre Telescope, which will hopefully help to image the black hole at the centre of the Milky Way.

Have a happy and safe holidays and we hope you’ll join us again in 2021!

This time-lapse video from the NACO instrument on ESO’s Very Large Telescope in Chile shows stars orbiting the supermassive black hole that lies at the heart of the Milky Way over a period of nearly 20 years. Credit: ESO/MPE

Feature Image

Artist impression of stars undergoing a ‘slingshot’ orbit around the supermassive black hole at the centre of the Milky Way. Credit: ESO/M. Parsa/L. Calçada

Related links

This week’s guests


Coming soon.

Episode 30: Pretty Planetary Nebulae

with Kelebogile Bonokwane

This week we’re joined by Kelebogile Bonokwane who is a National Astrophysics and Space Science Programme (NASSP) Master’s student at the South African Astronomical Observatory (SAAO).

Kelebogile talks with us about her MSc project on planetary nebulae. She is investigating whether binary stars sit at the heart of these magnificent structures and are responsible for their unusual shapes.

Her work utilises the Southern African Large Telescope (SALT) as well as NASA’s Transiting Exoplanet Survey Satellite (TESS). TESS is an all-sky survey mission designed to discover thousands of exoplanets around nearby bright stars. Kelebogile is using this data to study the central stars of planetary nebulae.

The “Starfish Nebula” Henize 2-47, a planetary nebula in Carina

Kelebogile was recently awarded the SAAO-SALT prize scholarship. She plans to do her PhD on X-ray binaries, investigating the relationship between X-ray and radio emission in order to study the accretion process and relativistic jet production.

This week’s guest

Feature Image

Planetary Nebulae He 2-47, NGC 5315, IC 4593, NGC 5307

Image Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Related Links

NASSP is a multi-institutional postgraduate initiative funded by the Department of Science and Innovation (DSI) through the NRF. The aim of NASSP is to train graduates in astronomy, astrophysics and space science in order to contribute to national programmes. Learn more about NASSP here.

SALT: www.salt.ac.za

TESS: https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite/


Social media by Sumari Hattingh.


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 world-class astronomy and astrophysics happening under African skies.

Jacinta: [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.

Dan: [00:00:23] Sit back and relax as we take you on a safari through the skies

Jacinta: [00:00:36] Hello and welcome to episode 30!

Dan: [00:00:40] Yay! Happy…Birthday? Yeah, 30th episode. Can’t really call it a birthday.

Jacinta: [00:00:49] Season 3 Episode 30.

Oh, that’s nice.

Dan: [00:00:52] Sure.

Jacinta: [00:00:53] Okay. 30. Well, we’re both in our thirties.

Dan: [00:00:55] Yes. Hubble’s 30 years old. We’re talking about Hubble! Well just a little bit. We’re talking about planetary nebula. Hubble takes nice photos.

Jacinta: [00:01:04] So I guess it was launched back in 1990 then. Yeah. Do you remember that year, Dan?

Dan: [00:01:09] Do you remember that year? Now I’m feeling old. It’s my birthday next week, happy birthday to me! Well, actually it will have been my birthday and I’ll be 36.

Jacinta: [00:01:23] I don’t remember 1990.

Dan: [00:01:25] I shouldn’t be telling people my age. Right, back to the episode.

Jacinta: [00:01:31] Before we get into the episode, what have you been up to this week, Dan?

Dan: [00:01:34] I put in a proposal for another planetarium film!

Jacinta: [00:01:37] Did you?

Dan: [00:01:39] I did. I put a funding proposal in for another planetarium film. And this time inspired by episode 28, a couple of weeks ago. The proposal for this one is African star lore. Finished. 24 minute film on African star lore. Multicultural, multilingual.

It’s going to be huge.

Jacinta: [00:01:58] I can’t wait!

Dan: [00:02:00] Yeah. Let’s hope they give me the money. Money is hard to come by. Right? What have you been up to?

Jacinta: [00:02:05] I’ve been attending the 2020 SARAO Bursary Conference. And SARAO is the South African Radio Astronomical Observatory. This happens every year and you’ve probably heard several of our episodes in the past where we’ve interviewed other people who are attending those.

So this year, of course, it’s virtual, it’s online. Just as the SAAO recent conference was online and it’s actually working pretty well. This year we have all pre-recorded quick 90 second talks, which get played in succession. And then there’s a question and answer session where people can ask us questions live and we are online to answer them.

And then we meet in this thing called Gather Town, which I hadn’t heard of before. But you’re kind of like in a video game and you’ve got your little avatar of yourself and you walk around the spaces of this online conference venue and you meet other people there and you can talk to each other. Because it turns your videos on and your sound on you talk to each other and it’s working surprisingly well, I really feel like I’m walking around and seeing these people who are on opposite sides of the world at the moment.

Dan: [00:03:10] That is weird.

Jacinta: [00:03:11] Yeah. So really well done to the organizers.

Dan: [00:03:13] Well I’m glad it’s working out.

Jacinta: [00:03:14] Yeah, it’s cool.

Obviously it doesn’t beat real life, but this is what we have to do at the moment.

So it’s working nicely.

Dan: [00:03:22] 90 second talks though!

Jacinta: [00:03:24] Yeah. That’s very quick, but at least everyone’s getting a shot to talk. So this is mainly for the post-graduate students and the post-docs who are being supported by SARAO and we meet every year and we’re hearing all about the amazing discoveries and detections that MeerKAT has been making this year.

So I think this was maybe the first time ever that we’ve had a particular session, which was this morning, dedicated just to new MeerKAT results. So, yeah, it’s the first year that they’re all just churning out and so many people have made so many different discoveries and it’s really exciting.

Dan: [00:04:00] And every is going to need an extra session.

Jacinta: [00:04:02] Hopefully. Yeah. That’s what we’re after.

Okay, so let’s get back onto this episode’s topic.

Dan: [00:04:09] So today we will be discussing?

Jacinta: [00:04:11] Today we’re going to be discussing planetary nebula, which are the endpoint of stars that are not particularly massive. So stars that are similar to the sun or maybe around two solar masses, meaning two times the mass of the sun. These stars, they don’t die in these big dramatic supernova explosions, which we often talk about. Rather, they kind of fade away.

So they start burning different elements other than hydrogen. And then they release their outer layers, which just kind of float off into space. And they are kind of lit up by the central remaining star or white dwarf, I suppose. And they create some beautiful colors that we’ve seen in pictures, particularly from Hubble.

Dan: [00:04:56] Yeah. So there’s these sort of cloudy shapes around the central star, which are in numerous different colors once they’ve been tinted. I think the shapes are incredible. They’re definitely some of the most eye catching images that come out of Hubble.

Jacinta: [00:05:13] So who are we speaking with today about these planetary nebulae?

Dan: [00:05:15] So today we are joined by an MSc student. She’s just finishing her MSc project at the University of Cape Town. And her name is Kelebogile Bonokwane. And she is from Kimberly in the Northern Cape originally, where our telescopes are. Not in Kimberley itself, but in the Northern Cape. And she’ll be talking to us about her project and some of the telescopes she’s been working on.

Jacinta: [00:05:37] Just a couple of things to mention.

First, sometimes she calls planetary nebula, PN for short. We also have a little discussion about spectrometry and photometry. So Dan, what’s the difference between those two?

Dan: [00:05:50] Photometry is basically collecting little photons of light and measuring how bright they are. And spectrometry is collecting little photons of light and measuring their frequency or wavelength.

So you can split them up into their constituent frequencies and look at the colours and frequencies, and you can tell completely different things other than just the brightness.

Jacinta: [00:06:14] You can hear some wind in the background there.

Dan: [00:06:16] It’s Cape Town. It’s summer.

Jacinta: [00:06:18] It’s very windy in Cape Town in summer.

Right. So that’s the difference between spectrometry and photometry and I think that’s all we need to know.

So let’s hear from Kelebogile.

Dan: [00:06:36] Today we’re joined by Kelebogile Bonokwane. Hello Kelebogile. Welcome!

Kelebogile: [00:06:41] Hi, thanks for having me.

Jacinta: [00:06:42] Welcome to The Cosmic Savannah. It’s a pleasure to have you.

Kelebogile: [00:06:45] I’m glad to be here.

Jacinta: [00:06:46] Can you tell us first just a little bit about yourself? Who you are, where you’re from and what your role is?

Kelebogile: [00:06:52] I am Kelebogile Virginia Stephanie Bonokwane. My mother gave me many long names.

So I am from Kimberly in the Northern Cape. I grew up in sort of a Kgosi township of Galeshewe. And right now I’m a bit of a student in transit between Masters and PhD in astrophysics. Specifically stellar astrophysics.

Dan: [00:07:20] Where are you based?

Kelebogile: [00:07:21] I am at the UCT and SAAO.

Dan: [00:07:24] So split between the South African Astronomical Observatory here with me, and at the University of Cape Town.

Jacinta: [00:07:30] With me!

Kelebogile: [00:07:32] Yes.

Dan: [00:07:33] Maybe you could just tell us a little bit about how did you get into astronomy? Where did you study your undergrad?

Jacinta: [00:07:38] What got you interested in the first place?

Kelebogile: [00:07:40] So I remember very particularly, I think I was in grade four and we were learning about the telescope and Galileo Galilei and I was like wow this is interesting!

And I sort of had this astronomy thing in my head ever since. Although I went to a technical school. So we did electrical, civil and mechanical technologies. I was like okay, maybe I might become an engineer. But I decided to just pursue astronomy instead. That’s what I found interesting. I was like, I’m going to be a scientist.

And so that’s when I came to Cape Town from Kimberley. I’ve been at UCT since undergrad. And I did physics as well as astrophysics majors in undergrad. And I decided to just stick to and pursue astronomy. It’s what I found interesting. It’s what I liked. And I wanted to be at a point later in my career where I was doing research and I was doing something that I really liked and enjoyed.

And so I am here now sort of in my post-grad continuing with astronomy.

Jacinta: [00:08:49] That’s

awesome. So what do you study? What’s your research been about so far?

Kelebogile: [00:08:53] So it’s been planetary nebulae since honours. Since my honours project. And I sort of continued with that into my Master’s project.

Dan: [00:09:04] Can you just explain for the listeners, what is a planetary nebula?

Because it’s not what you think it is, right?

Kelebogile: [00:09:10] Similar to people, stars evolve over a lifetime. They’re born and they die. And so the planetary nebulae, they are where a star evolves towards the end of its life time. And what happens is inside stars you have this constant, continuous nuclear reactions happening.

And you have these elements formed. Hydrogen, helium, the first few elements on the periodic table. So what then happens when a star becomes a planetary nebula, is that there’s been so much gravity on the star itself, that the temperature rises enough to sort of drive off the surface material off the star.

It does this through very strong winds. And so you have this expanded material of guests driven off the surface of the star and then this hard core at the center, sort of heats up this material. And that’s what you see as this glowing nebula. So that whole system is what you have as a planetary nebula. The core at the centre and this glowing nebula around it.

Dan: [00:10:20] And they have nothing to do with planets.

Kelebogile: [00:10:24] No.

Jacinta: [00:10:25] Do you know why it was named that way?

Kelebogile: [00:10:27] I’m not sure.

Dan: [00:10:28] I do. Actually I do. I mean, it was the earliest astronomers, maybe 200 years ago. I think it might’ve been William Herschel even. They were looking at these objects or seeing them through small telescopes and they looked more planet like than star like.

Because they had this extra sort of shape and colour. They’re beautiful objects, planetary nebula. We’ll post some pictures on the website. But Hubble has taken some incredible photos of planetary nebula. So I think that was why they were called planetary nebula at first.

Jacinta: [00:11:05] So it was thought that they were from planets?

Dan: [00:11:07] It was thought that they were planets. Cloudy planets or something going around a round planet. But now we know that, as you said, they’re the end point of a star’s life and have nothing to do with planets. In fact, if there was a planet there, then that probably wouldn’t end very well for


Jacinta: [00:11:23] So what do they actually look like, Kelebogile? Maybe you can tell us a bit more about the weird and wonderful shapes that they form.

Kelebogile: [00:11:31] Most planetary nebula are just spherical in structure or shape. But others have these bipolar lobes and jets, or these disks around the system. That’s what the ones look like that I’ve been studying. The sort of more interesting looking ones. The ones that have these interesting shapes that morphologies.

Jacinta: [00:11:57] And do you know why they have such strange shapes and morphologies?

Kelebogile: [00:12:01] Well, that’s sort of what we are trying to figure out. In the literature, it’s been speculated that it’s due to the stellar rotation and also others say that the magnetic field of the object can influence it. But those two scenarios don’t really support it, or wouldn’t be able to sustain that kind of shaping.

And so what’s been seen more recently is that there have been binary stars sort of discovered in these kinds of planetary nebulae. And so that’s what the basis of my research was. Trying to find binary central stars in these interesting PN  (Planetary nebulae) .

Dan: [00:12:45] Two stars within the planetary nebula itself? Or is the planetary nebula around the one star and the other star is further off?

Kelebogile: [00:12:53] Well, what you can have is the common envelope of the two stars. So most stars would reside inside of the common envelope and then the envelope can expand into the nebula and then sort of influence the shape like that. So that’s kind of what most simulations have modelled – how binaries can influence the shape of the planetary nebula.

Jacinta: [00:13:18] Okay. So there’s two stars in the very center and then the planetary nebula is very big and around both of them.

Kelebogile: [00:13:24] Yes.

Jacinta: [00:13:25] Okay.

Dan: [00:13:25] Oh right!

Jacinta: [00:13:26] Have you been looking into this problem with any particular planetary nebula?

Kelebogile: [00:13:31] Yes for my Master’s research, I looked at three objects. Hen3-1333,  Hen2-113 and Hen2-47. And Hen2-47 is the classically-known Starfish nebula. It looks like a starfish.

I looked at those because they were very interesting looking. They were all sort of multipolar in shape. So you had that interesting morphology, but also they had these extra features that added to how interesting they were and how they screamed that they must be binary central stars.

And that’s why I chose those objects. Those are the three that I looked at recently.

Dan: [00:14:15] And how are you observing them? Which telescopes are you using?

Kelebogile: [00:14:18] I used the South African Large Telescope SALT. And I also used the TESS telescope – the [Transiting] Exoplanet Survey Satellite, which is a space-based telescope. And the reason why I did that is because I wanted to do a very quantitative study.

So I got to spectroscopic data and also photometric data, to cover all bases.

Jacinta: [00:14:42] What kind of light does TESS collect? Is it optical light?

Kelebogile: [00:14:45] Yes.

Dan: [00:14:46] And it’s just collecting photometric data. So just brightnesses of stars, right? But it does that very regularly.

Kelebogile: [00:14:52] Yes, very.

Dan: [00:14:53] How regularly does it do it?

Kelebogile: [00:14:55] The data I had, it was taken at a 30 minute cadence.

And it does this continuously for about 27 and a half days.

Dan: [00:15:04] That’s amazing.

Jacinta: [00:15:05] So this satellite telescope is looking at the exoplanet every 30 minutes. Is that right?

Dan: [00:15:11] It’s looking at a field of the sky actually. So it’s looking at quite a large field of sky and it looks at it for 27 days consecutively taking an image every 30 minutes. So you’re looking at thousands of stars.

You didn’t use TESS specifically, you didn’t ask TESS to point for you. You’re just using TESS data, which they’ve released to you?

Jacinta: [00:15:31] From the archive?

Kelebogile: [00:15:32] Yes.

Jacinta: [00:15:33] And what did you find? What did you see?

Kelebogile: [00:15:35] Unfortunately, we had a non-detection in terms of finding the binary, but what we were able to do from our results is constrain the orbital period parameter.

And this is assuming that the features that we see, the shapes that we see, is because of a binary system.

Jacinta: [00:15:55] You were looking for a binary. You were trying to figure out whether these weird shapes were caused by binary stars at the center. You mentioned an orbital parameter. So you’re trying to find the amount of time it takes for the star to rotate around the other star?

Kelebogile: [00:16:09] Yes. And if you prove that does exist…

Jacinta: [00:16:13] then you’ve found a binary, right?

Kelebogile: [00:16:14] Yes.

Dan: [00:16:15] With the TESS data, you’re looking at the brightness of a star, or in this case the star at the center of a planetary nebula. And you’re looking for a change in its brightness, which will indicate that there’s another star there. Do these two stars have to be eclipsing?

I mean, does it have to be an eclipsing binary where the one passes behind the other in order for you to detect a dip in light?

Kelebogile: [00:16:37] It doesn’t necessarily have to be eclipsing, but you can tell from the sort of variation in the light curve that you make from this photometric data, if there is a signal detectable from that.

Jacinta: [00:16:54] Okay. So there could be some pattern in the light curve, even if it’s not eclipsing. Do you also look at the velocities of the stars? Like whether they’re actually wobbling?

Kelebogile: [00:17:03] Yes, so that was done with the spectroscopic data from SALT. I made radial velocity curves, and I had the light curves also to work from.

Jacinta: [00:17:15] Okay. So you’re looking at the variation in the light and whether the star is moving to figure out whether that’s a binary or not. Yes.

Dan: [00:17:22] So with SALT you’ve got a very high resolution spectrograph, a very high resolution spectrum. And from those lines, by looking at it at different times, presumably also fairly regularly, you can see  whether the star is moving towards or away from us. Correct?

Kelebogile: [00:17:38] Yes.

Dan: [00:17:39] And how regularly we were you doing that with SALT? How much data did you take from SALT?

Kelebogile: [00:17:44] It wasn’t an even sample, but the spectra that we had was taken over about 300 days. And so for the different objects, there was about 60, 58 and 35 amounts of observations. They were taken about 10 days between each observation. A little incoherent. So it was a bit of an uneven sample.

Dan: [00:18:11] So it was hard to find a sort of an easy period or pattern?

Kelebogile: [00:18:15] Yes.

Jacinta: [00:18:16] Were there any, maybe, slight hints of a binary?

Kelebogile: [00:18:20] There was for the Starfish nebula. There was this period that sort of stood out. It was 14 and a half days. What we do when we find a signal is that we try to phase up the light curve using that signal.

Jacinta: [00:18:36] Okay. So of the three planetary nebula you looked at to find binaries you’ve got “No. No. Maybe.” Is that right?

Kelebogile: [00:18:45] yes.

Dan: [00:18:46] Is the plan to carry on? Have you got plans to collect more data and try and clarify some of these things?

Kelebogile: [00:18:54] Well, because our results were saying no short periods, which is less than 10 days, we are assuming that they have very long orbital periods. And so we just need a little more data, or a lot more data! Because we have about three years of observations and we are assuming that the orbital period should be at least around thousands of days. So we need a lot more observations and monitoring with SALT to pin down if there is something.

Jacinta: [00:19:30] Okay. So your results don’t necessarily mean that there isn’t a binary. The obit of the stars around each other could be on a much longer time scale than you’ve already had a chance to look at.

Kelebogile: [00:19:40] Yes.

Dan: [00:19:40] And that wouldn’t be that long. If it’s a thousand days, that’s two and a half years or something.

That’s a slightly bigger orbit than the Earth, but not massive when you’re looking at two different stars. How big are these planetary nebula on the scale of the Solar System?

Kelebogile: [00:19:57] Very big. I guess if the Sun were to go into its planetary nebula phase, it might absorb Jupiter, I think.

Jacinta: [00:20:06] Oh, cool.

Kelebogile: [00:20:07] Yeah.

Dan: [00:20:09] That’s pretty big!

Jacinta: [00:20:10] Yeah!

Kelebogile: [00:20:12] And then there won’t be Earth by then.

Jacinta: [00:20:14] No. What would happen to the Earth?

Dan: [00:20:18] Vaporized.

Kelebogile: [00:20:19] Yeah.

Dan: [00:20:21] Vaporized.

Jacinta: [00:20:22] Yeah. I guess it would be already eaten up when the star becomes a red giant, right?

Kelebogile: [00:20:27] Yes.

Dan: [00:20:28] Is the sun expected to go into a planetary nebula phase? What are the requirements for a star to go into this phase?

Kelebogile: [00:20:36] Planetary nebulae progenitors, which are the first stages of the star are similar to the Sun. So they have similar masses, which is around two solar masses. So you would expect the Sun to follow the same evolution as a regular planetary nebula. So you would expect it to go into a planetary nebula phase.

Dan: [00:20:59] Yeah. So first it expands into this big red giant, and then that will kind of dissipate into a planetary nebula phase. Oh, that’s not a bad way to go.

Jacinta: [00:21:08] And do you know why they make all of these beautiful colors?

Kelebogile: [00:21:11] So it’s the elements often and then sometimes also the part of the spectrum it’s observed in. But for PN, from what I can tell, it’s mostly the elements.

So you have oxygen, nitrogen and sulfur making the blue, green, and red that you see. And those colors are sort of composites made. And then that’s how you see these different colors or what you would have perceived the PN to look like.

Jacinta: [00:21:44] So, do you think you would see those colors if you looked at it with your eyes or are they sort of false color images meant to represent the emission of different chemicals or elements inside the planetary nebula?

Kelebogile: [00:21:56] It would be because of that. False colors.

Jacinta: [00:21:58] Yeah. We spoke to Jayanne English a few episodes ago and she was actually one of the people at NASA who was making the image composites.

Dan: [00:22:06] And from Hubble too. So she presumably did play with some of the planetary nebula.

Jacinta: [00:22:11] Yeah, maybe even some of these planetary nebula. What are your plans for the future?

Kelebogile: [00:22:15] Well for now, I think I can only tell you about three or four years into the future.

Dan: [00:22:21] Oh, that’s more than I could say.

Kelebogile: [00:22:24] I’m starting my PhD next year, early next year. And that’s sort of going into a bit of a new field in X-ray binaries, working with X-ray and radio data. Which is something very, very new for me. But it’s an exciting challenge, I guess. But it’s still sort of sticking with stellar and binaries. Sort of a theme that I have going on.

Dan: [00:22:49] Where will you be doing that?

Kelebogile: [00:22:50] I will be at the SAAO. Okay, cool.

Jacinta: [00:22:53] Okay. Congratulations!

Okay, great. So I think when we’re nearly at the end now. Do you have any final messages for listeners?

Kelebogile: [00:23:00] Well, if they’re already listening and watching this, they’re already doing something good. But a message for them, I’d say, continue to listen and watch, learn about the science and whatever interests you in the field.

And also just continue to expose yourself to the different people that come here and tell you the paths they’ve taken to get to where they are. It can be something inspiring for you as an individual, regardless of whatever you are doing. And just continue to take care of yourself, stay safe with these times that we are in and be kind.

Jacinta: [00:23:42] That’s fantastic. Is that the advice you’d give yourself if you could go back in time and see little you when you were in grade four and interested in astronomy.

Kelebogile: [00:23:51] Yes.

Jacinta: [00:23:52] Great.

Dan: [00:23:53] Thank you. And thank you for your inspiration.

Kelebogile: [00:23:55] Thank you so much.

Dan: [00:23:56] It’s greatly appreciated.

Jacinta: [00:23:58] Yeah. Thank you very much for joining us and we hope to speak to you again soon.

Kelebogile: [00:24:01] It was nice being here.

Jacinta: [00:24:11] Okay. So interesting to know that these pictures of the planetary nebula, which have fascinated me since I was also very young, are false color images.

Dan: [00:24:19] Yeah. So we’ve discussed this previously, as you mentioned, episode 17 if you want to go back and listen, and we chat to somebody who does exactly that. So it’s more than just making up some false colors to make it look pretty. It’s not just sticking it into Photoshop and making it look nice. They actually try and hold onto the science. So adjust the image according to its frequencies and then use the different colors to represent those frequencies. So you actually, to use quite a big word, ‘elucidate’.

You shed light on what exactly is going on.

Jacinta: [00:24:52] Yeah.

Dan: [00:24:53] Yeah, a great chat to Kelebogile too. It’s really cool to hear stories of people who grew up in South Africa, getting interested in astronomy at a young age, and then having the opportunity to study it and become an astronomer. It’s really special and wonderful to see.

Jacinta: [00:25:10] Yeah, definitely.

Cool. All right. Well, it was really awesome to talk to Kelebogile. 

Dan: [00:25:15] Yeah, and we’ll let you get back to your Bursary Conference. Some exciting science I’m sure coming out and hopefully we can earmark some people to interview, including yourself. And l keep trying to get you to talk about your new paper.

Jacinta: [00:25:28] It’s not accepted yet, but as soon as it is…

Dan: [00:25:30] okay. Soon, soon, soon.

Jacinta: [00:25:32] Yeah. I’ll be the guest on one of the episodes.

Dan: [00:25:36] And do let us know if there’s anything else exciting coming out of the conference.

Jacinta: [00:25:40] Oh, there is. I’ve already written a whole list of people that we need to interview on what their topics were.

Dan: [00:25:44] Ah excellent.

Jacinta: [00:25:45] And I’ll let you get back to your funding proposals.

Dan: [00:25:47] Yeah. I’m just holding thumbs at this point,

Jacinta: [00:25:52] which for those not in South Africa means crossing fingers. That’s the very South African phrase.

Dan: [00:25:57] Oh right, yeah! I alway forget that that’s a South African thing.

Jacinta: [00:26:00] Okay. Well, that’s it for today. So thanks very much for listening and we hope you’ll join us again for the next episode of The Cosmic Savannah. You can visit our website, thecosmicsavannah.com where we will have the transcript, links and other stuff 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.

Dan: [00:26:22] Special thanks today to Kelebogile Bonokwane for speaking with us.

Jacinta: [00:26:26] Thanks to our social media manager Sumari Hattingh and all the Cosmic Savannah volunteers.

Dan: [00:26:31] Also to Mark Allnut for the music production, Janus Brink and Michal Lyzcek for photography and Lana Ceraj for graphic design.

Jacinta: [00:26:38] 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.

Dan: [00:26:48] You can subscribe on Apple Podcasts, Spotify, or wherever you find your podcasts.

And if you’d like to help us out, please rate and review us and recommend us to a friend.

Jacinta: [00:26:56] We’ll speak to you next time on The Cosmic Savannah. [Music ends.]

Uh, and we also have a little discussion about photometry and spectromedy…Oh. [Laughs]

Dan: [00:27:14] Do you want to leave that in there?

Jacinta: [00:27:17] No, that can be for the bloopers.


Dan: [00:27:20] And that’s it for today. Thanks very much for listening and we hope you’ll join us again for the next step of the next ep… why is that one first?

Jacinta: [00:27:26] Cause that’s always first.

Dan: [00:27:27] Is it? It feels like it should be last.

Jacinta: [00:27:29] No, we have it again at the end. “We’ll speak to you next time on The Cosmic Savannah.” Don’t question the method now! We’re three seasons in! [Laughing]

Dan: [00:27:40] I was like, this doesn’t make sense. It seems so final!

Jacinta: [00:27:41] It does, doesn’t it?

Dan: [00:27:43] What’s TikTok? Should we join TikTok?

Jacinta: [00:27:45] I don’t know Dan.

Dan: [00:27:47] I don’t know. I’m 36 now.

Jacinta: [00:27:49] Yeah, I’m not going to say how old I am, but I’m a bit younger than you.

Dan: [00:27:53] Not far. [Laughing]