Episode 57: From dust to dust

with Dr Omima Osman

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We are joined by Dr Omima Osman, a lecturer at the University of Khartoum in Sudan, who recently completed her PhD at the International Centre for Radio Astronomy Research (ICRAR) in Western Australia.

Omima’s PhD research was all about cosmic dust. She explains how this dust forms in the death throes of massive stars, how it grows in interstellar space and how it’s then, in turn, destroyed again by the death of stars.

Omima also spoke to us how her research into the “stickiness” and “chance of destruction” of dust grains can have an impact on simulations of star formation, and therefore our understanding of how galaxies evolve.

This Week’s Guest


By Moloko Makwetja and Justine Crook-Mansour

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

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

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

[00:00:24] Dan: Sit back and relax; as we take you on a safari through the skies.

[00:00:31] Jacinta: Hello, everyone. Welcome to episode 57.

[00:00:34] Dan: Dust? Anybody?


[00:00:38] Jacinta: Oh my God.

Daniel just said that to me. This is before we started recording and I looked at him like he was an idiot. And then he explained to me that it’s a reference. Would you care to explain to our dear listeners, Dan?

[00:00:51] Dan: It’s the reference from Little Britain, which if you haven’t seen Little Britain, take a moment. It’s ridiculous comedy.

Anyway, back to the task at hand.

[00:01:01] Jacinta: Okay. Anyway, we are talking about dust today. We are speaking with Dr. Omima Osman, who is from the University of Western Australia, International Center for Radio Astronomy Research, (ICRAR). It’s a long acronym there. So UWA-ICRAR, and yeah she’s just finished her PhD in studying dust.

Cosmic dust

[00:01:25] Dan: Well, yes. We’re talking about the dust out in space, around stars, interstellar media, and how it forms and how we go, sort of. I wanted it to say that there’s the thing everyone always says we’re all stardust. And today we’re talking about the stardust.

[00:01:41] Jacinta: Yeah. That’s right. We are essentially all made of stardust.

All of the, I guess elements that make us up were almost all forged in supernova, right?

[00:01:55] Dan: And I guess we’ll hear a little bit more about it from Omima, but you know, that stardust has to condense into some sort of form a planet, a rock, and ultimately a human. So we can take a couple of steps in that direction.

I don’t think we’re going to cover the entire way, through evolution and everything else to where we are, but maybe we can take a first couple of steps today with Omima.

[00:02:17] Jacinta: Yeah. So I had a really great time talking with Omima here in Western Australia, about dust and, it’s something that I’ve never really learned much about.

I mean, I know that within galaxies, there are stars there is huge clouds of gas, this huge clouds of dust. You know, we can see the dust clouds blocking our view of the centre of the Milky Way. When we look up at the sky at night, especially if you’re in the southern hemisphere, you can see the big dust clouds. But I never really thought about what it actually is and why it’s important in the galaxy and what happens to it.

But Omima explained really well why dust is important in galaxy evolution, which, you know, once she said that I immediately became interested because we all know that’s kind of my field of interest. And she was kind of talking about the lifecycle of dust. So how it’s forged in the death throes of massive stars or even smaller stars, you know, either through supernova explosions or through this thing called AGB, which is asymptotic like, what do they.

It’s Asymptotic Giant Branch. Okay, good. Everyone. See, I remember my undergrad. Asymptotic John Branch stars, AGB stars. Which kind of just means stars that are at the end of their life. Kind of like what will happen to our Sun at the end of its life. The outer layers will just kind of. Just stop drifting off into space.

And the metals in that area will form the dust or the more violent form of creation, which is like the supernova explosions. And then how the dust is. It’s the stuff between stars, the interstellar matter or ISM, as we like our acronyms. So, you know, we always think of the space between stars. It’s like empty vacuum, but it’s actually not.

It’s got lots of stuff in it. It’s got dust, and it’s got gas and it’s got molecules. So Omima tells us like, what’s going on with this dust, as it’s floating out there between the stars, what happens to it during its lifetime, how it grows and how it can be destroyed at the end. And actually, I didn’t realize how important the role dust plays in letting new stars form.

So I won’t spoil it, but that’s kind of the whole life cycle that Omima is going to tell us about.

[00:04:31] Dan: What is the difference between dust molecules and gas?

[00:04:35] Jacinta: So that’s actually a really good question and Omima answers that. So we’ll discuss that again at the end. Shall we hear from Omima?

[00:04:44] Dan: Perfect.

[00:04:52] Jacinta: With us today is Dr. Omima Osman.

Welcome Omima.

[00:04:55] Omima: Thank you so much Jacinta. It’s lovely to be here.

[00:04:58] Jacinta: It’s amazing to be able to speak with you today. First of all, for our listeners, can you tell us a bit about yourself, who you are and where you’re from?

[00:05:05] Omima: Certainly. Omima Osman from Sudan. I grew up and spent most of my life in Sudan, and then I spend a few years studying partly in Italy and here in Australia.

So I have just finished my PhD at University of Western Australia. And I’m a lecturer at University of Khartoum.

[00:05:27] Jacinta: Wonderful. So, first of all, tell us a little bit about that experience if you’re happy to do so, you know, what was your pathway through studying in Sudan and then ending up in Australia via Italy?

[00:05:40] Omima: Okay. Yeah, certainly I’m always excited to tell my story because I think it’s really important to travel around and see the world. I experienced different cultures and different systems, especially education systems. So I graduated from the faculty of science in 2010, University of Khartoum, major in physics.

And then I moved in 2011 to the International Centre for Theoretical Physics in Italy. I did the one year. Before I moved to Trieste University, which is also in Italy to do a masters in astrophysics and cosmology. I loved my time there. I always say that Trieste is my second home. And then, couple of years, well, actually four years before I started my PhD here in Australia.

So I finished my masters in 2014. And then I started my PhD in 2018. And I have just finished my PhD and I love staying in Trieste as well, so that I have three homes.

[00:06:46] Jacinta: That’s wonderful. What an international adventure. That’s an amazing story. Okay, so three homes, Sudan, Italy, Australia. Tell us the truth.

What do you think about Western Australia?

[00:06:57] Omima: Honestly, at the beginning, I hated Western Australia. I mean, it wasn’t a love from first sight at all. But then it just grew on me. I mean, I had the chance to go around to different beaches here in Western Australia, different cities. I have seen the ocean and I have seen the river.

I have seen the desert. I have seen the bush. So I just fell in love eventually and I think it’s the strongest love ever.

[00:07:28] Jacinta: Awesome. Well, that’s the correct answer. Of course listeners know this is where I’m from. I’m from Perth in Western Australia. So I’m glad that you managed to like fall in love with it eventually, which is awesome.

Okay. So tell us a little bit about your science. Now, you’ve just finished your PhD, and you are now doctor. So congratulations for that, First of all. What did you study?

[00:07:53] Omima: Yes. Thank you so much. Yeah, I did my PhD in cosmic dust, which is something I think many people have heard about. And I don’t know, for some reason they are just excited about it.

When I say I have studied cosmic dust, everyone lifts up and ask me what is cosmic dust. So basically cosmic dust is the dust that is produced by the stars. So, and it makes interstellar medium, or the space between the stars is actually not empty. It’s full of material. That is gas as well as very tiny solid particles that we call cosmic dust.

And this dust is produced by the dying star. So if you have a star that is exploded in supernova explosion, then this is what it produces. It produces metals. And some of those matters just solidify to form dust. So that’s basically the dust that I’m interested in, and it’s so tiny that some people say it’s the smoke, basically not dust.

[00:08:59] Jacinta: All right. So you basically study stardust, right? Or star-smoke in a way.

[00:09:06] Omima: Yes. It’s stardust , and they always love the expression that says “dust to dust, from dust to dust, to dust, to dust”. Which is like, capturing it perfectly because you start from a dying star and then the dust itself influence how the stars are formed.

So it’s kind of a loop.

[00:09:28] Jacinta: Dust to dust. That’s awesome. Hopefully that’s the name of this episode. Okay. So you mentioned that dust is created by stars and, then is destroyed by stars. Can you tell us more about that life cycle of the dust.

[00:09:40] Omima: Yes, sure. When the stars are about to die, so the stars themselves have their own paths of life and evolution.

And in their last stages of life, we have two different types of endings of star life. One of them is AGB stars. So, when the star is stopped, burning hydrogen, and it starts burning helium. And then just puffs off, and it starts to lose the external layers of the star. And in this stage, all the matters that are produced by the star, they cooled down and solidify, partially to form dust.

And the other ending is supernova explosions. And in those explosions, a lot of the material also is ejected of the star, and as the ejector is expanding, it cools down and also solidify into dust. So this is the initial source of the stardust, AGB stars, and supernova explosions. And once the dust is formed by those stars, it expands and and mix up in the general interstellar medium.

So that it’s not anymore in the vicinity of the star, it’s more in the general interstellar medium. And when it arrives to there, then it’s subject to different kinds of processes. One of them is destruction. So, but now we are still expanding in this kind of medium. So, the pre-existing dust is actually destroyed by the new supernovae expanding.

So it’s the source and in the same time, a sink for dust. And when the dust arrive into more dense environment like Milka clouds, so it’s more protected and it has a chance to grow in size and mass by accreting metals from the environment. So those are kind of, the main processing that is driving the dust revolution.

There are other details, but I think those are the main things.

[00:11:46] Jacinta: Well, so that’s really a life cycle, isn’t it? So they’re created this, the dust is created by the stars and then it kind of spends its existence. Growing into kind of more dust in interstellar space, and then it’s eventually destroyed by the same kind of supernova explosions that acrreted it in the first place.

So tell us more about what happens to the dust during its, I guess it’s not alive, so you can’t say lifetime, but during its existence, you mentioned that it can kind of grow or accrete. What do you mean when you say accrete, and how can dust grow?

[00:12:23] Omima: Yeah, sure, indeed. So dust, there are very small kind of solid particles that are just kind of floating in the interstellar medium.

And in this interstellar medium, there are other kinds of, well, let’s say atoms. There are lots of atoms, different types of like oxygen, silicone, magnesium. They’re also floating in the same kind of environment and, they frequently collide with the dust grains. And when they collide with the dust grains, they stick to the grain, resulting in a grow of the grain in mass, as well as size, but it’s not always, certainly like they don’t stick 100%.

They sometimes they just fly off that the surface. And this is basically how it grow. It needs frequent collisions, as well as the availability of those types of methods.

[00:13:16] Jacinta: All right. So when you say the dust is accreting, you’re saying that there’s these particles, whatever metals, whatever, it might be like oxygen or silicon on stuff, and it’s hitting the dust grains, and then it may or may not stick to the dust grains.

And then if it does, like this dust grain grows and then you kind of get this growing of dust clouds, I suppose. Does it always stick?

[00:13:37] Omima: Well, no. As I said, it sometimes the matters just fly off, of the dust surface. And this depends on a lot of things on the density, for instance, of those matters, how frequent they collide with the dust grain, and also the physics of the dust grain itself.

For instance, if it’s a surface that have high affinity, to the matters that are arriving in, then they really stick strongly to the surface. And it will be hard to be removed by, for instance, temperature fluctuations. But if you have a surface that is fully covered, for instance, with hydrogen atoms or when it’s covered with hydrogen atoms, then that means there’s no interaction sites on the dust grain surface. So, you don’t stick. The matter simply just don’t stick and in this instance, it’s not 100% ability of sticknes.

[00:14:32] Jacinta: That’s so cool. I’ve never heard of that before. Okay. So, if I understand correctly, you’ve got your dust grain and then you’ve got your metal hitting it.

And if the dust grain is covered in hydrogen atoms, it actually means that the metal can’t stick. It has a low level of stickiness, but if the hydrogen atoms aren’t there, then it has a high level of stickiness. Is this new? Did we know about this before?

[00:14:54] Omima: It’s not a new thing. Actually, we have known this for a long time for maybe over two decades, but it’s more recently that this field of research is started to be rejuvenated, because at some point it was just dropped off, like in the mid-eighties. And then now with higher the solution kind of hydrodynamic assimilations that we have today, and that we can implement those models that the field had kind of picked up again. But yeah, at least the physics of what is going on, we know to a good extent, I would say. Yeah.

[00:15:32] Jacinta: May I make a dust pun.

[00:15:35] Omima: Yeah, sure.

[00:15:38] Jacinta: So, the topic of dust stickiness was left on the shelf for a longer, bit dusty.

[00:15:43] Omima: Yes. I would say that. Yes.

[00:15:47] Jacinta: I’m very proud of myself for that one. Dan’s going to tell me off.

Okay. So you’re talking about simulations. Is that what you did for your PhD? Did you do some simulations of this dust, stickiness and growth?

[00:16:01] Omima: Yeah, I used the mainly hydrodynamic assimilations for my PhD to study dust, because we have a lot of theoretical models, but we haven’t been implementing them in hydrodynamic assimilations.

In the nineties, we have been merely looking at those using One-zone models. And those are not quite sufficient because you look at the galaxy as whole. And we know by now that, it depends on their location in the galaxy, and that’s why hydrodynamic assimilations are very suited for those kinds of studies, because we have a relatively better resolution to look actually at those certain patches where the dust more or less form more efficiently, or destroyed more efficiently. And we can understand exactly what is going on.

[00:16:52] Jacinta: Cool. So you use massive supercomputers. And in them you create model universes. You like you simulate universes. Well, you see me like galaxies and the stars and the stuff between them, so the interstellar matter. And then specifically you’re using these simulations, which we have talked about before on the podcast, but not very often. You’re using these simulations now to study the dust and in particular, what happens to the dust during its existence in how it grows, and it grows by stickiness. Right. So what did you find, how, how sticky is dust?

[00:17:29] Omima: Okay. Yeah. So, this is very interesting because people usually assume that in many of the models that I have seen and many of the applications, they assume that matter is stick to the dust 100%. So they just assume one, but due to many factors that I have excepted earlier that the physics of the surface, the interstellar medium conditions and everything, the matters doesn’t certainly stick to the dust grain, and what I found with this study, using simulations as well as observation. So I use observations as constraints of my simulation, so that I can constrain those, this parameter in particular. And I found that it’s between 50 to 100%, and 100% is not most of the time. So it’s most of the time, somewhere in between. What I found is the stickiness could be as low as 50% all the way up to 100%.

So it’s not all the time like that. And I use observation to constrain those models. So, the results are pretty much reliable, I would say.

[00:18:36] Jacinta: Okay. So you’re using simulations, and comparing them with observations and the observations say, okay, galaxies or the interstellar medium can have maximum this much dust or minimum, this much dust or something like that.

You use that and say okay, I know that, and now my simulation, I will only allow it to have this much dust. You know, you use it to set your parameters of your simulation. And then what you found is that dust stickiness can be 50%. So there’s a 50% chance that the matter will stick to the dust or not. Or up to a 100%, and this is important because previously a lot of people have been assuming that it’s a 100% chance.

So if the matter will hits the dust, it definitely sticks. So, they’ve been assuming this when they’ve created theoretical models for things. Theoretical models for what? Why do we actually care how much dust there is and how sticky it is?

[00:19:27] Omima: So why do we care about how much does we have? I mean, this is really a tiny fraction of the interstellar medium. It’s only 1% of the interstellar medium, but it has huge influence on the galaxy evolution. And this is because of two reasons. The first one is the fact that, dust influence the same dynamical balance of interstellar medium. So it influence how the interstellar medium cool and heat. Which means, you also influencing, by extension, the density of the interstellar medium, which means you are influencing how much stars you have. How much star formation you have, and the more or less you have stars forming, it’s influencing how your galaxy as hole is dynamically, morphologically evolving.

But also because dust is the most efficient pathway for the formation of molecular hydrogen. We know that there are gas phase pathway, and then there is the dust phase pathway. The gas phase is not very efficient. The efficient pathway is when the hydrogen atoms, both of them meet on the dust grain surfaces and then interact to form molecular hydrogen. So without those, we basically don’t have as much hydrogen, we don’t have as much dense environment from stars, and then we have less efficient star formation. So basically we owe dust, all the stars that we see today in the night sky.

[00:21:05] Jacinta: All right. So now we’re talking about galaxy evolution, which is my field. So now I’m on track now. I’m understanding what was going on. Okay. So, we want to know how galaxies evolve. A big part of that is, how many stars they’re forming. Their star formation rate. So, and then we need to know, okay, so if we want to figure out how much star formation there’s going to be, or we’ll be in a galaxy, we need to know how much of their raw fuel there is. Their raw fuel of course, is hydrogen gas, which first is, you know, all floating around in the interstellar space as nice neutral hydrogen gas, which I talk about a lot on the podcast because I work on HI, neutral hydrogen gas also, as our listeners will know.

So we’ve got that like nice, boring hydrogen gas just sitting there doing not very much. But then when the conditions arise in the interstellar medium, so when there’s the correct density and the correct temperature. So when it’s, I think you’re going to correct me in a moment if I’m wrong, but I think it has to be quite cool and it has to be quite dense. Then the hydrogen atoms can combine together to form molecular hydrogen, and it’s inside those clumps of molecular hydrogen that fusion can start and you know, baby stars can form.

So, what I think you’ve just told us is that the dust grains are like the dating app, of hydrogen atoms, which just gives them a platform to come together and meet each other and hold on to each other and create molecular hydrogen, which then leads to the formation of stars, which then leads to galaxy evolution.

Does that sound about right?

[00:22:37] Omima: Oh, yes. I love the way you put it as a dating app. Yes that’s exactly what happens. So what happens is you have your dust grain. It has much more surface than just having the hydrogen atoms, either forming molecular hydrogen or just bouncing off. But when you have them on the surface, what happens is the phrase hydrogen. It finds interaction site, active interaction site, and it’s like strongly bound to that side. So it’s not mobile.

And then you have another hydrogen atom which is still hopping on the surface. Then find that, tied hydrogen to the surface and then just interact with it. And once they interacted for molecular hydrogen, then the interaction is actually exothermic. So the energy released from the interaction will be enough to eject the molecule from the surface. And that’s how we get the molecular hydrogen.

[00:23:35] Jacinta: Ah, I’ve always wondered how molecular hydrogen is formed. And now I know. So the dating app, where one atom is kind of trapped in the other one comes to it. Okay. Let’s. We’ll probably stop the analogy there, otherwise we’ll get into trouble but, basically they all right, so then you’ve got this coupling of the two hydrogen atoms. It results in an exothermic reaction, which means it releases heat, which means it releases a photon of light, which allows the two atoms to let go of the dust and combine together as nice molecular gas.

And then presumably that photon means that energy has been released from the system. So the system has cooled down. So your gas, your interstellar medium has now cooled down. Is that correct? Is that, is that how it cools?

[00:24:24] Omima: So, molecular hydrogen formation is, I think it’s a little bit of a delicate kind of formation process. I don’t know the full details of it. So basically when you have your molecule is tightly bound to the surface, it’s kind of, it’s ground state, and it’s like, when you are trying to remove electoral from atom, you have to give it some energy. It doesn’t matter what kind of energy is. So it could be a thermal energy, it could be a mechanical energy, but you just have to give some kind of energy so that you can remove it from the surface. And this is what happens with molecular hydrogen. So your molecular hydrogen as a molecule is really tightly bound to the surface, and you have to give it this energy. And this is what happened when they are interacted.

There is this kind of energy. Where does it go? It’s basically absorbed by the dust grain, and then the dust grain is not in the stable state. So, it ejects your molecule, hydrogen molecule. But I think it’s more complex than that, but this is just my understanding of it.

[00:25:31] Jacinta: Cool. So it’s complicated. And, also, probably like that little photon of energy that the molecular molecules giving the dust atom is like the payment for the app. I’m assuming. And he says, this is a paid app, right. This one’s not free. So, I think I’ve taken that analogy far too far now. So we’ll move on to, okay. That’s what happens during the life of the dust.

And that’s why the dust is really useful for the galaxy to help it form stars. Now, you also mentioned from dust to dust, so the stars then destroy the dust. Tell us more about that what’s happening there. And how destructive is this process?

[00:26:03] Omima: Yes. Okay. So. How does it destroy it? Because as I mentioned earlier, the interstellar medium is a very harsh kind of environment.

There are all different kinds of explosions going on and you have also star formation. New stars, like just putting tremendous amounts of energy to the interstellar medium. So, it’s not a medium that you really would like to be in, unless you have to. So, when the dust is in the interstellar medium, and then you have supernovae going off nearby, what happens is that the supernova sweeps up the gas as well as the dust, which is mixed into the gas.

And what happened? The gas particles that are in that sweeped up gas, it start to, like collide with the dust grains like crazy, and starting to weather it out. So eventually, a bit by bit it’s like, it’s really like atom by atom. So in every collision you have a few atoms, like weathered off the surface of the dust grain.

And then this continues. If you have really small dust grains, they will just vanish, and if you have big enough dust grains, and when I say big enough, that one micron, a one micron kind of grains, those could survive the explosion. But, by the end of the day, you actually lost some mass of the dust because these ones they’re weathered out of the dust. They go to the gas phase in a form of metals. So you increase your matters in the gas phase, but you decrease them in the dust phase. And this process is actually very efficient. For long time we thought the dust is just formed and destroyed. But when we did the maths, we found that if it’s just destroyed, then we will not have as much dust as we have today.

So we figured out that the dust has to grow in the interstellar medium, and this is where the growth came in. It was proposed, but then we also figured out it’s actually happening in the interstellar medium.

[00:28:22] Jacinta: Well, so that’s fascinating. So we previously thought that, okay, supernova goes off, destroys all of the dust, but then that doesn’t explain how much dust there is. So, they can’t all get destroyed. Is this part of what you worked on during your PhD? And what did you find?

[00:28:37] Omima: Well, yes. So as much as I looked at the sticking coefficient, I also looked at how much of the dust is destroyed. So I looked also at the destruction fraction, and this is because we have a lot of theoretical models, and the results we have from those models, like very like crazy. Some of them tell us for certain type of dust, we have 100% destruction, and some of them give us as low as 9%. So, the range is just huge. So, I use the same kind of observations I use to constrain the sticking coefficient to also try and constrain the destruction fraction. And for that we found about 40%.

[00:29:21] Jacinta: Right. So the supernova can only destroy about 40% of the dust.

[00:29:25] Omima: Yes, that’s true. Before we have the dust growth, we have only 20% of the dust that could survive supernova explosions. And in some studies it shows even 10%, not 20%. So, without having growth. Supernova will just destroy most of the dust we have in the interstellar medium.

[00:29:48] Jacinta: Just one final question because I’m finding this so fascinating. We could talk all day. When you say dust, I mean, obviously I think about just all of the dust, that’s coating all of my things at home that I have been ignoring and not dusting. Is that the same sort of dust as what you’re talking about? Or are they different? And how how are they different?

[00:30:05] Omima: I think there is a vast scale between the dust we have here on Earth and the dust we have in the interstellar medium. There’s actually different types of dust. We have the dust that is surrounding the stars that are just formed. So what we call young stellar optics, and there’s dust, which is surrounding the dying stars.

And then there’s the dust that is in the interstellar medium. She’s the one that I study. And finally, the dust that we received by tonnes on Earth, is the interplanetary dust. Which is a dust that is like coming from burnout meteoroids and asteroids and whatever really we trim from the solar system.

But all of what we receive in air, here on earth. Mostly it’s not coming from the open interstellar medium, but rather from the limited space we have in the solar system.

[00:31:04] Jacinta: That’s so cool. So now I can go and dust the interplanetary dust off my bookshelf. Thank you so much Omima again for joining u. It’s been an absolute pleasure speaking with you.

And just before we go, do you have any final messages for listiners?

[00:31:17] Omima: Yeah. Okay. Thank you so much Jacinta for having me. It has been lovely talking to you. I always get very excited talking about cosmic dust or really the, whatever it is that I’m doing. So please get in contact if you’d like to talk further about this, I’m happy. Or you can look up my papers there on the arXiv under Osman, my surname to 2020. So you can get both papers and yeah. Thank you so much. Thank you for having me. I think that’s all. Thank you.

[00:31:51] Jacinta: Thanks very much.

[00:31:59] Dan: So, what is the difference between dust molecules and gas?

[00:32:04] Jacinta: Well, based on what Omima said, I think it’s, well, I loved how she called it. “Cosmic smoke”. How these particles of quote unquote “dust is so small that it’s kind of more like a smoke”. So then the question, yeah. What is the difference between dust and what is gas?

I think was, that the dust’s molecules clump together or atoms clumped together enough to be on the size of like the giant ones are on the size of one micron. One micrometer large. And then when the supernova comes through and everything bumps together, she was actually saying how the atoms is stripped off like one by one in each collision.

And so that atom that’s stripped off becomes gas, you know, because it’s a atom floating by itself and it’s not bonded with anything else. And so, yeah, it kind of just eventually dissolves and becomes gas.

[00:32:57] Dan: Yeah. So I think that we have this earthly impression of dust, and it’s very small. You can’t really see it floats around the, you can just see it floats around in the air, but you can’t see gas like, you know, gas is individual atoms, you know, a lot of the gas is small molecules. But dust is slightly bigger. It’s clumps of molecules which have formed into this dust, which then in space doesn’t settle on your desk, but it travels around like a smoke.

[00:33:27] Jacinta: Yeah, that’s right. And then it’s, as we were saying, it’s kind of like the dating app of hydrogen atoms so they can, you know, get together for molecular hydrogen.

And then essentially it helps with the cooling process. So dust helps cool things down. Which is kind of the opposite of what a dating app does. It’s meant to heat things up, but anyway, let’s stop with that analogy. We’ll stop with that analogy I’ll get in trouble, but you know, anyway, cool things down and then it manages to form stars. So, dust is important in forming stars.

[00:34:02] Dan: Yeah, that’s great. Like looking at the whole life cycle of dust, you know, and as we said, at the beginning, we’re all are stardust and ultimately we will be again. But, it’s kind of cool to see how the dust is helping form the stars, getting reformed when they explode, because inside a star, it gets completely destroyed in that process, but then gets recycled and the elements that make it up, get recycled and sent back into space to make more stars and planets and little creatures.

[00:34:34] Jacinta: Like us.

[00:34:35] Dan: Like ourselves.

[00:34:39] Jacinta: Oh great. Yeah, no, I thought that was… It was really cool to learn about dust. Yeah.

[00:34:44] Dan: And great to hear from Omima, who’s had an interesting journey from Sudan through Italy, to Western Australia. And just amazing to see how her career has progressed. And I look forward to seeing how it progresses further.

[00:34:57] Jacinta: Yeah, exactly. And she’s headed back to Sudan now for a little while, and she’s got a lectureship there. I think, at the University of Khartoum and yeah. Looking forward to seeing what she does next.

[00:35:09] Dan: Great. Thank you very much for the interview.

[00:35:11] Jacinta: Yeah, you’re very welcome. We were sitting in the recording studio at the University of Western Australia, which I managed to find. Although I’m not sure if I meant to be admitting it out loud, but anyway, they’ve got a really nice recording studio with carpeted walls and floor. And it’s so quiet, Dan, we need one of those,

[00:35:30] Dan: Well we had one of those, but then COVID came and,

[00:35:33] Jacinta: well, yeah, this was very professional.

[00:35:36] Dan: Yeah. Ours had character.

[00:35:40] Jacinta: Yeah. That’s right. Any echoes that you hear listeners it’s just character.

[00:35:45] Dan: Before we go; Jacinta, how are you?

[00:35:51] Jacinta: Yes. Oh, well, thank you for asking Dan. I’m great,

[00:35:56] Dan: It it?

[00:35:57] Jacinta: Yes, I am. I had a very exciting weekend. I finally managed to achieve one of my dreams, which was to give a TED talk.

[00:36:06] Dan: Oh yes. Congrats.

[00:36:08] Jacinta: Yeah. I spoke at TEDxMandurah, which is my hometown and it was so much fun. It was just, oh my God. It was like one of the best experiences of my life.

I found it really difficult, now you’ve given a TEDx talk before, haven’t you done?

[00:36:24] Dan: I have indeed.

[00:36:25] Jacinta: So how did you find the experience?

[00:36:27] Dan: Also, I mean, it was pretty fun too. It was so formal. I mean, normally you give a talk at a conference or something and you know, you put your slides together that morning over breakfast, and then walk in kind of half wing it, you know, you get questions and it’s like, it’s a formal talk, but it’s not as formal.

Whereas with TED, you know, you really delivering. So you have to have your thoughts and your notes. Everything is pretty streamlined, well thought out you’ve kind of practiced the words you’re going to say, even, and. I still work, I still winged it a bit, but,

[00:37:06] Jacinta: It’s your style.

[00:37:07] Dan: It is my style and yeah, but like super cool, the feeling behind it and it feels really special and, yeah. How was your experience?

[00:37:17] Jacinta: Yeah, it was very different, like you were saying very different to any other thing I’ve done before. We actually had weekly training for quite a few months beforehand. Workshopping of our talk. We didn’t have to go, but I went to most of these, and we kind of give our practice talk or, you know, whatever we had at the time we get feedback from the other speakers and the workshop leads.

And I found that really useful. I really put a lot of effort into it because I wanted to, make quite a lot of different points, but bring it all around into the one argument. The one idea worth sharing, which for me was the title of my talk was, “how can giant telescopes help humanity?” And so I wanted to take people on a journey through kind of astronomy, and radio astronomy, and the universe, and then bring it back down to the Earth and how it relates to our actual lives.

So, I ended up scripting it word for word, and then memorizing it word for word, which is something that I don’t. Yeah. Which is something that I, I’ve not really done before. I usually do the same as you kind of know what I want to talk about, but not exactly the words I’m going to use. And, actually it turns out to be very, very difficult to memorize word for word, like a 20 minute talk.

[00:38:31] Dan: Now, I can imagine.

[00:38:34] Jacinta: Yeah. And so the dress rehearsal was like two days beforehand or three days beforehand. And it did not go well. And so it scared me. I needed a prompter,

[00:38:44] Dan: because you couldn’t remember your words, not because you didn’t know what you were talking about.

[00:38:47] Jacinta: Yeah, for most sentences. I got like, almost a little bit of like stage, not fear, but like struck, you know, like my brain just went empty,

[00:38:57] Dan: stage fright.

[00:38:57] Jacinta: Stage, well suppose stage fright. Yeah. And I was just like, oh dear.

[00:39:02] Dan: Hahaha what have I done?

[00:39:03] Jacinta: So I spent the next few days just practicing it and yeah, it ended up going really well on the day. The first time that I got through the entire talk, start to finish without making a mistake or forgetting a bit was onstage.

[00:39:19] Dan: Well, it’s amazing what stress can do.

[00:39:21] Jacinta: Right. and adrenaline.

[00:39:22] Dan: Your brain operates on another level.

[00:39:24] Jacinta: Exactly. And, you know, before the talk started, I was backstage, you know, like getting

[00:39:30] Dan: hyperventilating

[00:39:31] Jacinta: ventilating, but just like that rush of adrenaline. I wasn’t nervous. I was just really excited. We had hair and makeup that morning. I’d been up early, you know, getting ready, looking good, happy with my outfit. And yeah, and it’s also really special because that particular stage that we did the event on, I grew up on doing endless dance competitions and school pantomimes and awards nights and all of that stuff.

So I’m very familiar with that beautiful theatre. So it was a really nice like full circle, having been around the world with my career and coming back, even though, you know, I’m stuck here at the moment, but whatever. Let’s pretend it was intentional, to be able to give the TED talk on that stage. So yeah, I was really happy with it.

And then once I came off stage, my ears were like, not ringing, but like, the adrenaline was like pulsing in them. So, I couldn’t hear the talk after that because I was so excited, but yeah, no really, really great experience. And I’m looking forward to seeing the video. I really hope that it came across as good as it felt, because I don’t want to be disappointed by the video and be like, ah, I didn’t know I looked like that.

[00:40:38] Dan: If I’m honest, I don’t think I watched one.

[00:40:40] Jacinta: You didn’t watch yours?

[00:40:42] Dan: No ways.

[00:40:43] Jacinta: Really?

[00:40:43] Dan: I hate watching myself.

[00:40:44] Jacinta: Really?

[00:40:45] Dan: I mean, I used to, like, when I first started doing the TV and things, I used to watch myself just to like, try and give myself feedback, like, oh, don’t say that, oh do this better or whatever. But it gets to a point where you can obsess over it and say, we know, I could have done that better.

Whereas the live performance is what it is. And the fact that it’s live is half of the joy, and that it’s not perfect. So, you know, it feels natural.

[00:41:14] Jacinta: Yeah. Interesting. Because in this one instance, I guess I was doing it a lot more for the video than the audience. Like obviously it was for the audience, but there was only like a very limited audience because of COVID and everything. So lot of it was for the video. I wonder, like watching it, I might be like, do I really stand like that? Why hasn’t anbody told me.

[00:41:39] Dan: Well, we’ll be sure to share the video as soon as it arrives.

[00:41:41] Jacinta: Yeah. So that you can all judge me.

[00:41:42] Dan: And if I can get hold of any of Jacinta’s ballet videos

[00:41:49] Jacinta: No. Absolutely not. Anyway, Dan enough about me. How are you?

[00:41:53] Dan: I’m also well, thank you. I am not feeling so overwhelmed at the moment, which is really nice. It’s winter in Cape Town, which is very cold and wet, but that’s fun. And yeah, I have a couple of exciting projects coming up. We’ll be making another planetarium film, hopefully just a little one. Which is always very exciting for me. And I have a bit of travel coming up too. So, heading to Europe and at the end of the month. Which is great. I haven’t traveled in a few years now.

[00:42:23] Jacinta: Travel. How dare are you?

[00:42:24] Dan: No I know, right. I know what it’s going to be like, hoping I can get through the airports. Multiple PCR tests. I think we’ll be in the offing, but yeah, I’m excited feeling energized and looking forward to the next few months.

[00:42:38] Jacinta: Great. Yeah, we should also mention that this episode we plan is to be the penultimate one of the season. So next episode will probably be a review of the, I don’t know, year plus, how long has it been since we started, these season? Like a really long time ago.

[00:42:55] Dan: I have no gauge of time.

[00:42:56] Jacinta: No. Time doesn’t really mean anything.

[00:42:58] Dan: It last a little while.

[00:43:00] Jacinta: Yes. So we’ll do a little bit of a summary and then we’ll take a break because Dan’s traveling, and I’m starting my first lecture course that I’ve ever run. So, Ooh, wish me luck that. Alrighty. I think we’ve prattled on for a long enough. So, that’s it for today. Thanks very much for listening and we hope you’ll join us again for the next episode of The Cosmic Savannah.

[00:43:23] Dan: As always, you can visit our website, thecosmicsavannah.com. We will have the transcript, links, pictures and other stuff related to today’s episode.

[00:43:31] Jacinta: You can follow us on Twitter, Facebook, and Instagram @cosmicsavannah. That’s Savannah spelled S, A, V, A, N, N, A, H. You can also find us on YouTube, where audio only episodes are uploaded with closed captions, which can be auto-translated into many different languages, including Afrikaans isiXhosa, and isiZulu.

[00:43:51] Dan: Special. Thanks today to Omima Osman, for speaking with us.

[00:43:54] Jacinta: Thanks to all social media managers, Sumari Hattingh, and our audio editor, Jacob Fine.

[00:43:59] Dan: Also to Mark Allnut for music production, Michal Lyzcek for photography, Carl Jones for astrophotography, Susie Caras for graphic design, and Justine Crook-Mansour, and Moloko Makwetja for transcription.

[00:44:08] Jacinta: We gratefully acknowledged support from the south African National Research Foundation, the South African Agency for Science and Technology Advancement, the South African Astronomical Observatory, and the University of Cape Town Astronomy department.

[00:44:21] Dan: You can subscribe on apple podcasts, Spotify, or wherever you get your podcasts. And we’d really appreciate it, if you could rate and review us and recommend us to a friend.

[00:44:29] Jacinta: And we’ll speak to you next time on The Cosmic Savannah.