Ep. 677: The Answer is Always Dust

Whenever astronomers discover something surprising, the answer often turns out to be dust. Dust obscuring our view, dust changing the polarity, dust warming things up, dust cooling things down. It’s always dust. Until it isn’t.


(This is an automatically generated transcript)

Fraser Cain [00:01:49] Astronomy Cast Episode 677. The answer is always dust. Welcome to Astronomy Cast for weekly, facts based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain and the publisher of Universe Today. With me is Doctor Pamela Kay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Hey, panel, how are you doing? 

Pamela Gay [00:02:11] I am doing well. I have to admit, dust is one of those things that likes to get involved in every aspect of our lives, and we’ve avoided this show for a long time. But at a certain point, the dust catches up with you. 

Fraser Cain [00:02:26] Is it a is it a spring cleaning thing? Is it an allergies thing? Something put dust into our minds? Maybe it’s the dust itself choosing this show. 

Pamela Gay [00:02:36] It’s like microplastics. It’s in everything. 

Fraser Cain [00:02:39] Yeah. As Carl Sagan said, we’re made of star dust. 

Pamela Gay [00:02:43] Are microplastics technically dust? 

Fraser Cain [00:02:46] I don’t know. 

Pamela Gay [00:02:49] They probably. 

Fraser Cain [00:02:49] Should. We just stop the show right now and dig into this? No, no. We’ll put a pin in. You will wait for the helpful emails. 

Pamela Gay [00:02:57] That’s true. 

Fraser Cain [00:02:57] Which is? Which is being written right now. Oh. All right, well, whenever astronomers discover something surprising, the answer often turns out to be dust. Dust obscuring our view. Dust changing the polarity. Dust warming things up, dust cooling things down. It’s always dust until it isn’t. So I guess before we talk about how it’s always dust, what is dust in astronomically speaking. 

Pamela Gay [00:03:23] It is, molecules of stuff, and the molecular nature of it is kind of the key. And the molecules can be really, really big, like polycyclic aromatic hydrocarbons. Pages. They can be things like methane molecules. But dust is, is where you start to get collections of larger and larger molecules coming together. This is where you start seeing amino acids and eventually as dust bigger, you start getting grains of ices and grains of silicates and and eventually things get big enough that we no longer refer to them as dust. But that stuff we can’t generally see at a great distance. 

Fraser Cain [00:04:13] So what would be? What would be no longer dust? 

Pamela Gay [00:04:17] Dust is really defined at a certain level by its behavior. If you have a cloud of dust and you shine light through it, it is going to preferentially scatter out the shorter wavelengths of light. You’re going to see the blue getting sent sideways. This is how you get the really cool reflection nebulae, while the longer, redder wavelengths are able to make it through. And as the dust gets thicker and thicker, you’re eventually only going to get the longest shades of infrared light coming through. But once you start getting to things that are big enough that they’re just like, hi, I am solid, right? It’s just going to block light. 

Fraser Cain [00:04:57] So when the moon passes in front of the sun and we get an eclipse, that is not dust. 

Pamela Gay [00:05:02] That’s right. 

Fraser Cain [00:05:03] Dust. Okay. So I think that sets an upper boundary. And what about a lower boundary. Like when is it too small to be dust. 

Pamela Gay [00:05:10] Well so this is where you start getting at the gas dust boundary. And and so like if you have a cloud of carbon dioxide carbon monoxide, you can see all of the molecular line transitions. And and it is behaving like a gas. Now once you start saying we’re seeing polycyclic aromatic hydrocarbons. Is that necessarily a gas? No not really. That’s a really, really big molecule. So we’re starting to call things dust. And so the question becomes exactly at what point do you say that molecule is sufficiently complicated that we’re going to refer to it as, as dust. And this is where I think a lot of people gloss over. What is the boundary between these two things by, by looking at, oh, that’s an amino acid, that’s EPA. And by naming it instead of saying dust versus gas, right. You avoid the entire problem once it’s ionized. It’s a it’s it’s a gas. 

Fraser Cain [00:06:19] Right. But but it sounds like you did put like one pretty big constraint on it, which is that you get this, this bluing of the light as it’s passing through it all, or. 

Pamela Gay [00:06:33] A reddening of. 

Fraser Cain [00:06:34] The light that’s passing through it. Like I think about smoke, like when we have we have forest fires here on the west coast of Canada. And there are times when you can see the sun with your unaided eye because it is hidden behind so much smoke. 

Pamela Gay [00:06:50] Yeah. 

Fraser Cain [00:06:51] Don’t do it. But but it’s but it’s there. And so the light from the sun is not getting obscured by the moon or, you know, boulders thrown into the air. There is something that is changing the nature of the light that is coming from the sun to us. And yet the rest of the time you’ve got air, nitrogen, carbon dioxide, oxygen, various atoms that are in the air in between us in the sun. And they’re not doing that same kind of thing. So it’s this range where gas ends and rocks begin. Yeah. And it changes the nature of the light as it passes through to I sort of have constraints on. 

Pamela Gay [00:07:38] Yes, yes. And it starts to get ugly. There was a paper a couple of weeks ago, I think we both covered on a newly discovered, or newly understood exoplanet that is, large and far, far, far away from the pair of cool stars that orbits. And so it has silicon grains in its upper atmosphere that range in size from the the most diffuse smoke you’ve seen coming off of a candle, two grains like you’d experience in a sandstorm. And and so I think that way of looking at it. But then you start getting to the is this grain starting to be called a rock? And. 

Fraser Cain [00:08:25] Yeah. Okay. So now that we’ve defined dust and like, you know, to ask astronomers to define dust is to then begin a two hour argument where people will just describe the terminology. And you may not get the answer by the end of this conversation. So so, you know, we’re not going to cover it in this podcast. But. What can dust do to mess up your observations? 

Pamela Gay [00:08:53] Everything. I think the day that I was like, oh, no, it even affects me. And I think every astronomer who’s had this at a certain point while working my dissertation, I was, trying to estimate the distance to galaxy clusters by looking at the colors of the galaxies in the clusters, because we didn’t have spectra to use yet. And I had to take into account how much the color of the galaxies gets shifted by the dust within our own galaxy. And I had to do the. All right. There are five different maps to use. This is the one that’s most referenced. All right. I will use this map. And it’s very unsatisfactory because people have done their best to look at a variety of objects that should all be the same color to to look in different wavelengths, to all different methods of trying to figure out how to effectively map the dust. Looking for tracer species that we can see in millimeter radio light. And at a certain level, it’s not like we can actually go out and measure of the dust. And, and we just know it’s out there affecting the color that we see. Thanks. And while I can start to make estimates of how much dust is within the Milky Way, who knows how much dust is just, like, randomly scattered through the universe between me and the galaxy clusters, I’m trying to estimate the distance to right. It gets annoying. 

Fraser Cain [00:10:31] All right, we’re gonna talk about that some more, but it’s time for another break. 

Pamela Gay [00:10:35] Like a lot of you out there. My heart belongs to science, but I still work to keep up to date with what’s happening in aerospace, from rocket launches to newly funded missions. I’m like you, I am a podcast listener, and bringing these two things together in one well-produced show is the Team Space Daily podcast hosted by Maria Vermeer. This scripted podcast summarizes space industry news and will help you keep up with all that is going on in commercial space, from Leo Labs to Space Acts. They are following the Launcher’s trackers and everyone in between. Every weekday. T-minus covers space tech, business and governance with analysis, intelligence briefings and engaging discussions with prominent experts from industry, academia, research organizations and government. This brand new show is the first space industry podcast to bring us updates every weekday, Monday through Friday. They are there to let you know who has launched, gone Bankrupt or landed that hot new contract. Stay current the easy way with T-minus SpaceX daily from end to K available all the places podcasts can be found, or check out their website at SpaceX that Entercom. That’s T-minus SpaceX daily your daily space industry podcast. 

Fraser Cain [00:12:04] And we’re back. So I guess, look, I think of an analogy like, say you had like a bright searchlight that was pointed at me. Yeah. And and then there was a fire in between. And now suddenly the color of the searchlight has changed from, say, bright white to red. And the brightness has changed from hurting my eyes to it’s not so bad. Yeah. And so now I can no longer be certain about what color the light was. Right. The searchlight was. And I can no longer be certain about how far away the searchlight is, and I can’t be certain about how big the searchlight is, like, all of. 

Pamela Gay [00:12:43] These things are true. 

Fraser Cain [00:12:44] All right. So. So what characteristics does dust have on the observations that you try to make on some kind of object? 

Pamela Gay [00:12:57] So first order it makes things redder appearing right. Second order it makes things fainter. And which order. You put those two things and really depends on what you’re trying to measure. Then there’s also this really annoying characteristic of light going through dust getting scattered will end up having a preferential polarization. This means that as the light is moving through space, you have light waves. And the way those waves are oriented is is related to a whole lot of different things. One of which is, has that light been scattered off a surface like dust? And when we look at light and we see all the light has a similar way that those waves are going through space, we can say, yes, that was likely scattered by dust and that can mask other effects, or it can be caused at a place different than where the light originated. Right. And it can do things like confuse how we look at the cosmic microwave background, because there’s a whole lot of dust between here and there. 

Fraser Cain [00:14:10] So you’re describing those first order issues. So then what are the second order. Outcomes of of those issues. 

Pamela Gay [00:14:20] Everything we look at, we have to be a little bit concerned that what we’re understanding isn’t entirely true. To go back to the cosmic microwave background there, there have been various times that someone has been like we have just now it was dust. 

Fraser Cain [00:14:36] Right? But okay, you know what? I’m just going to hit you with a bunch of topics here, and you tell me if these are affected. The temperature of an object that we observe. 

Pamela Gay [00:14:46] Yes. 

Fraser Cain [00:14:47] The distance. 

Pamela Gay [00:14:48] Yes. 

Fraser Cain [00:14:48] The color. 

Pamela Gay [00:14:50] Yes. 

Fraser Cain [00:14:51] The size. 

Pamela Gay [00:14:53] Depends. 

Fraser Cain [00:14:54] I guess if we know. Okay. 

Pamela Gay [00:14:57] If it’s really resolved, it doesn’t change the size. 

Fraser Cain [00:15:00] Perfect. Okay, there we go. 

Pamela Gay [00:15:01] Although if we’re if it’s a binary system where we have other ways or if it’s system, it depends on the polarity. 

Fraser Cain [00:15:09] Yes. Like it just sounds like, like from those first issues, everything cascades. 

Pamela Gay [00:15:18] Yeah. 

Fraser Cain [00:15:19] Okay. Yeah, yeah. All right. 

Pamela Gay [00:15:22] It’s also cool. Well, literally it’s cold. Otherwise it wouldn’t exist. It would like, fall apart. But there’s things like, like our Corona Borealis starts that, like, will suddenly go high here is dust and fade dramatically. Right. So I mean, like dust does at least put on a show now in that magnetic fields. Magnetic fields are their own monster. 

Fraser Cain [00:15:47] Right. Okay. All right, all right. So then. Okay, so then how does an astronomer knowing that the that it is often dust. How do they go about figuring out that if what it is that they’re trying to observe is the result whole or in part by dust. 

Pamela Gay [00:16:13] So this. 

Fraser Cain [00:16:14] Is just like the the length of. 

Pamela Gay [00:16:16] U siding. 

Fraser Cain [00:16:20] I think we could wrap the podcast up right there. That just that just nailed it. But sure. No, please. Please go on. 

Pamela Gay [00:16:29] This is where you have to have multiple lines of evidence for a lot of things. So I think it can go both ways though. And this is where it gets frustrating. So like Beetlejuice 2019 decided it was going to not tell us that it was going to explode, but apparently forecast the coming of of a pandemic because that somehow fits with it. Someone put that in science fiction anyways, right? So so Beetlejuice back in 2019 went through this dramatic dimming and it just kept going through the first parts of 2020 and that dramatic dimming, people were like, well, is the star doing this? Is the star doing that? And a lot of folks were like, it’s it’s dust. But it was really hard to prove that it was dust. So it can go both directions and we just need multiple lines of evidence. If if you’re trying to understand the color of something, try and get it. Spectra, because the spectral will show you atomic lines and the the ability of an electron to jump between different levels and, and an atom is directly correlated to the temperature of that atom surrounding. So if you see this line in carbon, this line and hydrogen, these 40 lines and technician, that’s going to tell you accurately what the temperature of the object is. And then you look for the metrically at the well. It’s this bright in this red filter. It’s this brightness V filter. And you can start to get a sense of how what’s between us and the object is affected by dust. But you have to have those multiple lines of evidence. 

Fraser Cain [00:18:13] So back to this idea of spectroscopy, right. That you are seeing the chemical fingerprint of an object. And so you observe a star. You take the spectra of the star. You see the lines for iron, for for carbon, for whatever it is in the upper atmosphere of this star. If you put a whack of dust in front of you in that star, you still see that chemical fingerprint? 

Pamela Gay [00:18:40] Yes. 

Fraser Cain [00:18:41] It’s just redder. But that doesn’t. But the fingerprint will shine through it. 

Pamela Gay [00:18:48] Really? 

Fraser Cain [00:18:49] But it’s still there. 

Pamela Gay [00:18:51] You’re going to see the exact same absorption lines. And what’s interesting is you’ll sometimes, if you’re lucky, also see how the sunlight is exciting, the molecules to do interesting things in the dust. And this is where we really have to look at things across the entire electromagnetic spectrum to be able to see, okay, so the dust is having this happy little vibrational and rotational set of transitions, and the, star in the background is having these transitions and allows us to actually start to put together three dimensional temperature maps of what is happening as the light that we’re seeing passes through the space from where the light originated to where we’re observing it. 

Fraser Cain [00:19:39] So but could the dust generate its own? Could you be measuring the spectra of the dust itself and having. Yes, and have a hard time to distinguish between what is the star and what is the dust? 

Pamela Gay [00:19:51] Well, they’ll have very different temperatures. A star is generally sufficiently hot that it will photo ionized. Use the big words. The the the dust into component atoms. Dust requires cooler temperatures to exist. And and so if you’re seeing light that corresponds to, like Lyman alpha hot hydrogen gas, and you’re also seeing because you’re using a completely different telescope, the, carbon monoxide transitions, or the polycyclic aromatic hydrocarbon transitions, those those are two totally different temperature regimes that cannot coexist in the same space. 

Fraser Cain [00:20:40] Right? Right. All right. So I think we’ve we’ve defined our dust. We’ve explained how it messes things up. So how did dust confuse astronomers? On various discoveries. 

Pamela Gay [00:20:57] My my favorite three examples have already brought up Beetlejuice. Yep. The other one is I’m going to mispronounce and I apologize so much. Is Boyajian star or Tabby’s star? Yeah. And then of course, there there’s our Corona Borealis stars. Observationally, our Corona Borealis was the first one to be discovered. It was found in the 1700s. These are a class of star for which only a dozen ish examples are known. And they. They will be going along, going along with fairly normal periodicities of of changes in brightness, and then will suddenly go poof and disappear as they fade by as much as nine magnitudes. 

Fraser Cain [00:21:45] Wow. 

Pamela Gay [00:21:46] Yeah, yeah. They’re wild. And it’s thought that what happened is to lower mass white dwarf stars coalesced, formed a new orange giant star, and are just periodically shedding loads of dust. And so that’s a case of it took a few hundred years to figure out what was going on. And we’re now pretty sure that these massive drops in brightness are just dust coalescing. And that’s just really cool. 

Fraser Cain [00:22:22] But, I mean, I can think back to like, there was this map of the Milky Way. That was it. Herschel created, I think, like hundreds of years ago, that Herschel was trying to map the positions and distances to the various stars in the sky and built this map that surprise, surprise, had the sun at the center of the. 

Pamela Gay [00:22:45] Universe because of dust. 

Fraser Cain [00:22:47] Because of dust. That yeah, that that he just wasn’t able to observe the more distant objects until you got this blob that makes made him feel like, you know, he was like was literally drawing of the shape of the Milky Way as this. Yeah. As this, I don’t know. 

Pamela Gay [00:23:05] Well, so what do you what he did. What he did was he counted the stars in each direction. Yeah. And assumed that the density of stars on the sky related to how much Milky Way was in each direction. And when he looked towards Sagittarius and when he looked counter to Sagittarius, there were, in optical light, similarly ginormous numbers of stars. The distribution towards Sagittarius was bigger because we have the bulge in that direction, but he didn’t know that at the time. Yeah. And so by just counting the surface density of stars without having modern telescopic equipment and not being able to see in colors your eyeballs don’t see, and yeah, we were at the center of things. And the first time we really realized we weren’t at the center was I’m trying to remember who it was. I want to say oosterhouse, but I don’t think it was Oosterhouse. It was in the 1900s where they started looking at the distribution of globular clusters. And since globular clusters are in the halo of the galaxy, they have a spherical distribution and you can start to see that we aren’t in the center by looking at globular clusters. Right. It was a modern discovery because dust. 

Fraser Cain [00:24:27] Right, right. Can you give another example? I mean, I can throw a few more that I, that I’m aware of, but, you know, you talked about build you technical Bulgarian. Sorry, but but yeah like or and but then that much earlier example there was a fairly recent people remember Doctor Brian Keating and the team with the, with the Bicep2 observations. Yeah. They observed, primordial gravitational waves in the cosmic in the polarity of the cosmic microwave background radiation. Turns out it was dust. 

Pamela Gay [00:25:04] Yeah. 

Fraser Cain [00:25:04] Nobel Prize lost. 

Pamela Gay [00:25:07] On. 

Fraser Cain [00:25:07] Yeah, yeah. There’s some other examples that that. Where dust has has obscured the results, and it took a while for people to figure it out. 

Pamela Gay [00:25:18] It I think there’s just been a whole lot of stars over the years where we’ve been trying to understand what’s going on, and dust just left us a little bit foiled. And I have to admit that that there are so many examples of dust foiling people that I have chosen to mostly look at where dust was our friend. So, for instance, we were able to start figuring out, how stars form by looking in millimeter wavelengths of light for these cocoons of dust, where where stellar droplets were located. And I, I, I am a bit taken aback that we went with this biological language to describe it, but, yeah. So dust is the cocoon that hides where stars and solar systems are forming. And when we look out with the Atacama Large Millimeter Array at these systems, what we’re seeing is protoplanetary disks and a lot of cases that are constructed out of dust, with occasionally planets making their way through the dust, creating amazing eddies and dust lanes. And and so does does have a purpose. 

Fraser Cain [00:26:36] I think I mean, it definitely has a purpose, but I also think thanks to modern infrared astronomy, astronomers have a way to see through the dust. 

Pamela Gay [00:26:46] It’s true that we went from the collection of Bok globules, these called giant molecular clouds. And again, in a certain point, giant molecules become dust and giant molecular clouds are rich in dust. Right. And so these globules went from being these really cool for astrophotography, dark places on the sky to being things that we were like, oh, let’s go look through this with a different wavelength of light. And it’s convenient to have other wavelengths of light to look at things. 

Fraser Cain [00:27:20] That’s that’s cool. I mean, I think about, say, our ability now, like with the new images are coming from g, g t that they’re able to peer into these newly forming solar systems and see the planets. You know, there’s like an observation that came out a few months ago where they were able to directly observe the atmosphere of an exoplanet that’s only just a couple of million years old. Yeah. The ability to see through the zone of avoidance, you know, the gas and dust that obscures the center of the Milky Way to see what’s on the other side, you know? Yeah. 

Pamela Gay [00:27:56] It starts to let us go in the opposite direction as well. For decades, we understood that there was this gravitational thing that we named the Great Attractor, that great galaxies appeared to be moving towards, and we couldn’t see it because dust and, yeah, these longer wavelengths let us get through the dust and identify what is shaping the motions and shaping the formations. And dust basically blocks our view, conducts how everything should move, and is luckily susceptible to millimeter wavelength radiation. 

Fraser Cain [00:28:33] Yeah. I mean, I always find it hilarious when people are like, can you explain the Great Attractor? I’m like, yes. I mean, it has now been mapped, you know. 

Pamela Gay [00:28:41] For a while. 

Fraser Cain [00:28:42] It took a while, but now we know the locations of all the galaxies. And the mass of those galaxies explains the weird movement of everything sliding towards it. Done. Problem solved. Yeah. So are there any outstanding mysteries in astronomy where dust continues to make things more difficult? 

Pamela Gay [00:29:05] Well, there’s always going to be people who are like the reason that they type two a supernova look, the way they do is because there’s dust. There’s always going to be people. Basically any cool discovery saying it’s not actually a cool discovery because of dust. 

Fraser Cain [00:29:22] Right. 

Pamela Gay [00:29:23] Right. And it just gets exhausting. 

Fraser Cain [00:29:25] Yeah. I’m I mean, is it really that first instinct to astronomers to go, could this be dust? Do you think that’s like high up on there? I don’t know, science nervous system. 

Pamela Gay [00:29:37] So so there’s curmudgeons in every group. And and if you find something really, really cool, there’s going to be the curmudgeon who’s trying to disprove that you actually found something cool. And dust is going to be first on their mind because sometimes they’re right. And this like, we didn’t actually explain what Tabby’s Star is at all. It’s it’s this system that was observed to have remarkable depths of 20% of its brightness over periods of, of days. And. It. It was very strange, the pattern of increasing and decreasing, and we folks were able to go back through the historic record and find long term dimming. And, for a while people were like, have we’ve found the beginnings of a Dyson scarab? Right? Yeah. And and there was, I think, in all of this, this little, tiny, tiny hole. Yeah. Tiny, microscopic, too small to be called dust. Hope that maybe was a Dyson ring, but I’m. 

Fraser Cain [00:30:49] Not saying it’s aliens. Dyson swarm being it’s aliens. 

Pamela Gay [00:30:52] That’s right. And no, that was dust. It was just. 

Fraser Cain [00:30:56] Dust once again. All right, well, thank you, Pamela. So just remember, like, literally any interesting discovery that you ever make from this point on, any ailment that you experience, just ask yourself, could this be dust? 

Pamela Gay [00:31:13] The answer is probably. 

Fraser Cain [00:31:14] Probably. 

Pamela Gay [00:31:15] All right. Thanks for. 

Fraser Cain [00:31:16] That. 

Pamela Gay [00:31:17] Thank you. And thank you to all of our patrons out there who get ad free versions of this show through Patreon.com slash Astronomy Cast. This week we’d like to thank in particular Roland Vollmer, Dom Jeff Collins, Kellyanne and David Parker, Jeremy Kerwin, Stuart Miles or Mills, Harold Barden, Hagan, Scott Bieber, Kimberly Raich, Marco Rossi, Matthew Horstman, Alex Cohen, Georgie Ivanov, Daniel loosely DFM David Gates, consigliere. Pinch. Glencoe, Jim schooler. Disaster. Shriner, Scott. Cohn, Claudia. Mastroianni, Justin. Proctor, Matthias. Hayden, Gregory. Singleton, Jeff. Wilson. Cooper, Jim. Garage. And. Sorry. Tim. Garage and Tim McMeekin. Thanks, all of you, for allowing us to do everything we do. 

Fraser Cain [00:32:10] And we’ll see you next week. 

Pamela Gay [00:32:12] Bye bye. Astronomy cast is a joint product of the Universe Today and the Planetary Science Institute. Astronomy cast is released under a Creative Commons Attribution license. So love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Doctor Pamela Gay. You can get more information on today’s show topic on our website. Astronomy. Cars.com. This episode was brought to you. Thanks to our generous patrons on Patreon. If you want to help keep the show going, please consider joining our community at Patreon.com Slash Astronomy Cast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We are so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.

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