Daniel and Jorge Explain the UniverseDaniel and Jorge dust off their knowledge of the tiny-but-mighty grains of space dust which help form our world and block our view of the cosmos.
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Hey Daniel, you're kind of a neat freak, aren't you.
I do like to keep my laptop nicely well dusted.
Wait, dusted like you put dust in it or you take out dust or you wipe dust out of it.
Good question. I mean I like my cookies well dusted with sugar, but my laptop keyboard well dusted with zero dust.
Yeah, household dust is less delicious, and powdered sugar isn't regular dust like fifty percent skin cells.
That sounds like a pretty gross thing to put on your cookies. On the other hand, it would be pretty weird if powdered sugar just like accumulated.
In your house, it'd be pretty sweet.
We might call for some sweeping changes.
Uh, I'm glad you got to dust off that old punt.
Hi.
I'm poor haamdy cartoonas and the author of Oliver's Great Big Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And I don't like dust as much as astronomers do.
But do you still like it a little bit?
I like dust the way I like the sun. It's fascinating, it's interesting, it's useful. It tells us about the cosmos. But I don't really want it on my laptop or on my table.
But everywhere else it's okay.
Yeah, study it from a distance, you know, the way like I'm fascinated by cheetahs, but I don't really want to have a cheat on my lap.
Do you carry a duster with you at all times?
Then I actually do have this very fancy little machine for removing dust from your keyboard.
Is it called blowing on it? Or did you Did you actually pay for a machine to do that?
I actually have a nice little machine. It's really quite good. Yeah I should call it mini made.
Wait, what is it like a vacuum.
No, it's like a little blower.
You know.
It replaces those disposable cans that I thought were not very environmentally friendly, though I do love them.
Oh, I see you mean like the dust between the keys, like you want to get rid of it, like in the nooks and crannies.
Yeah, exactly. I like a nice clean keyboard.
Oh I thought you meant like on your screen, because I think you can just wipe that off.
I think you can, but probably that dust contains all sorts of fascinating stories where each of those bits has been.
But you know, if you just blow the dust, it's just getting in the air and then it's going to come back down on your keyboard.
I know.
It's a cycle. Unless I'm willing to live in a clean room, I can never escape it.
So you don't like living in clean rooms.
I don't have to wear a hairnet and booties all the time.
No, just some of the time. But anyways, Welcome to a podcast Daniel and Jorge Explain the Universe, a production of Our Heart Radio.
In which we dive deep into the cycles of the universe, the ones that produce massive stars and tiny grains of dust. Everything out there in the universe has a history and tells a story, and if we can unpack it, unravel it, and study it, you can reveal those stories and the history of our own cosmic to learn about the formation of the planets and stars and the universe itself, from the biggest clues to the tiniest speck of dust.
That's right, we blow the dust off of the universe, trying to uncover what's underneath, what shiny surface or interesting facts are there for us to understand and to learn about.
I love in archaeology how every time they're going to discover something amazing, they always have to blow dust off of it, pull cobwebs off of it. That's like your visual cue that you're about to learn something ancient.
Wait, wait, what do you mean?
I mean? I just watched a New Indian Jones. I guess. So you know, anytime they unde earth something from the olden days, it's always covered in dust. Of course.
MM.
To see they carry a duster with them at all times. Maybe you can buy one of those devices and you didn't have to waste electricity.
I'd be that neat freak archaeologist. I don't think i'd get very far in the field.
Yeah, it is a dusty universe full of amazing things, where even the dust is interesting in the universe.
Down here on Earth we see dust as sort of a nuisance, something to brush out of our way. But out in space dust places it's a very important role in the formation of stars and planets, and it can reveal that history. Dust is not just a nuisance. It's a fascinating pile of tiny clues.
So today end podcast, we'll be asking the question how important is cosmic dust? Now, hopefully this episode won't be a bust.
Should we just be sweeping cosmic dust under the cosmic rug or should we take it seriously and study it in detail.
M that's a bit of a dusty pun there, you used it already, but yeah, it's an interesting question here. Cosmic dust I guess it's different than regular dust.
Well, I think there's fewer dead skin cells and leftover bits of insects out there floating between the stars than there is here on Earth. But cosmic dust also falls to Earth.
You mean it gets sprinkled from space like powdered sugar.
Well, you know that space isn't empty, and there's dust out there between the stars but also between the planets, and as the Earth moves through these cosmic dust clouds, it accumulates some of them. Some tons of dust fall to Earth every year from interplanetary space out there in the Solar System.
WHOA is it like dandruff space dandruff? Or is that too embarrassing?
We had a whole fun episode about where this stuff comes from. It's a bit of a mystery. There's a recent experiment though, that tries to pin the blame on Mars. It might be that dust storms on Mars are blowing that stuff out into space, and the Earth is flying through Mars dust clouds. So yeah, I guess it's all Martian dandruff.
Yeah, Mars needs some head and shoulders.
Well first they need to heads and shoulders. That'd be pretty awesome.
Discovery yeah, or maybe just a hat that might help. But it is an interesting question. How important is cosmic dust? Which I guess means Daniel, that cosmic dust is important.
Cosmic dust is more important than you might think. I mean, the word dust makes you think it's insignificant. It's just something to be blown off of. Something else. Man, it gets in your way something, It messes things up, something to be gotten rid of. But dust has clues in it. This is like the dust here on Earth tells you who's been living there and the insects that have been around. Dust out in space tells you what's been happening in the universe because there's dust makers and dust consumers, and dust also plays a big role in making stars and planets.
Well, you just said dust consumers out in space, like aliens who buy dust.
That's what it sounds like, not dust customers. You know, ways in which just is created and then dust is destroyed. I should say dust destroyers.
Oh there you go. See that's a device. I would buy a dust destroyer.
Wait till you learn how dust is destroyed. You don't want one of these things?
Maybe I do. Let's find out. Well, as usual, we were wondering how many people had thought about the importance of cosmic does and what role it has in our search for the meaning of the universe and how it all works.
Thanks to everybody who pitches in for this segment of the podcast. I hear from listeners that they really enjoy hearing your voices in your thoughts on the episode topic. If you would like to share your voice and thoughts, please don't be shy, write me too. Questions at Danielandjorge dot com.
So think about for a second, how important do you think cosmic dust is? Here's what people have to.
Say, stop waving from the universe. I would say that twenty percent is planet stars, black holes, sixty percent gus, and the rest twenty percent is dust.
I think that this is the one of those questions that but you have to think about some things that you usually take for granted. So I would say that the MUQA is mostly composed by dust.
All right, interesting answers here. Some people seem to interpret the question as like how significant is cosmic doest?
Yeah?
Like, or like how much how much of the universe is cosmic does?
And they also seem to be taking it as a leading question, like because I'm asking it. They're figuring probably it's a big component of the universe and playing an important role.
I see, it wouldn't be very interesting. Answer was just like not at all or nope, nobody cares.
Yeah, Like how important are Daniel dirty socks? Yeah? Not interesting, not important? Move on, that wouldn't be a very fun episode.
Let's not talk about your socks because I know you don't wear socks, so.
Well, then it's a philosophy question, right can my socks be unimportant if they don't even exist?
There you go, philosophy of footwear.
Somebody out there is doing a whole PhD Thesis on that topic, probably.
On your socks.
On socks and jacky.
I know you're famous now, Daniel, but geez.
No on socks? Why they disappear? Where they go? Why dryers consume them? See dryers are sock destroyers, nye. It turns them into dust. Maybe it transports them to the hozone layer of the atmosphere.
So let's dig into this topic, Daniel. What is cosmic dust?
Cosmic dust is an important part of the solar system, though it's not a big fraction of the solar system. The answer from these listeners made me dig into the question of like, actually, what is the mass budget of the Solar system? How much of it is cosmic dust, and how much of it is made of other stuff?
So what's the breakdown?
So the Milky Way weighs about one to one and a half trillion times the mass of the Sun. That's like our mass unit a solar mass, and the total Milky Way is about a trillion trillion and a half solar masses. Now, most of that, like ninety percent of that is dark matter. We know that the stuff that's visible in the universe, the stuff that glows, and even the stuff that doesn't glow that much, like rocks and dust and asteroids, that's only like ten percent of the mass of the Milky Way. Out there in the larger universe, dark matter is a little bit less common than it is here in the Milky Way. The Milky Way has more dark matter than an average galaxy.
And I guess how do we know these things? Like how do we know how much the Milky Way weighs? Do we put it on a scale or something?
We can measure the component of the Milky Way independently and then add them up. The stars and the interstellar medium and the black hole. All that stuff we can measure independently, and then we can measure the total by looking at how fast the Milky Way is rotating. Because stars are like tracers, they move around the Milky Way, and their speed is determined by the gravitational traction of everything closer to the center than they are. Things further away from the center on the outer shell don't affect them at all, things on the inside do. So by reading the speed of these stars, we can tell how much mass their radius encloses, and so that measures the total mass of the Solar System. And that's how we infer dark matter, sort of the left over bit that we can't account for with stars and planets and gas and dust.
But we can't see all of the Milky Way, right Like we're in the Milky Way, Can we really see the full extent of it and have a good guess about its composition.
There's a lot of uncertainty, which is why I said one to one and a half trillion solar masses. So that's like an uncertainty of five hundred billion solar masses. And yeah, part of that comes from the fact that we can't see the whole Milky Way because we're looking through it, we're inside of it, and the Milky Way has a good amount of dust in it, and that dust obscures our view. So there's a whole region of the Milky Way that we can't see very well in many frequencies of light, and that leads to a lot of this uncertainty.
I see. So, then how much of our Milky Way is dust?
So it's like ninety percent dark matter, Then it's like three percent stars, it's like one hundred to two hundred billion stars, and then leftover is this stuff called the interstellar medium, which is maybe like half a percent or one percent of the mass of the Milky Way, and one percent of that is dust. The interstellar medium is mostly gas. It's like hydrogen and a little bit of helium. So one percent of the interstellar medium, which is one percent of the galaxy, is dust. So the dust is like pointzho one percent or maybe half of that. It's a tiny fraction of the mass of the Milky Way.
So I guess you don't count that gas is dust, right.
That's right. And this is another example of humans putting categories on things where really there's a smooth spectrum. If we call it gas, it means it's like a molecule, there's like h two floating out there, we call that gas. If it's a larger clump of stuff, bunch of molecules together, little grains dound like one hundred nanometers or larger, we call that dust. Get much bigger, we start to call you like a meteor or an asteroid or even a planet. But in the end there's a whole spectrum all the way down from individual molecules which we call gas, to larger clumps of stuff which we call dust, all the way up to much bigger objects stars and planets.
I guess at some point you get to like pebbles, right and little rocks. Is there such a thing as space sand?
Well, you know this dust is made of carbon and silicates, right, and sand is mostly silicates. So in the end, like a lot of this space dust is kind of like super fine grains of sand.
But then I also imagine there is sort of sand sized grains out there in space.
There are larger pieces for sure, and so this intermedia category we call dust is not a very big fraction of the mass of the Milky Way. But to compare it's about the same mass as the central black hole. Point oh one percent of the Milky Way. Sounds like a tiny number. It's a tiny percentage of a huge number, right, one and a half trillion solar masses. So it comes out to be about the mass of the central black hole.
And so where did all this dust come from? Like are there giant space aliens shedding of their skin?
To understand where the dust comes from, we need to dig into a little bit more about like what is this dust? And it's made of like a bunch of different stuff. Some tiny little portion of it, this is really fascinating, comes from the atmospheres of stars. We know that stars their job is to take hydrogen and helium and lighter elements and fuse them into heavier elements although I have to iron and even heavier in the case of supernova. And in the atmospheres of these stars, especially when they get really really big and near the end of their life, their atmospheres produce these little grains. They're like coalesce as they cool, and the outflow in the atmosphere of these stars. That's sort of like one source of this stuff. But if you look out into the universe, and study this stuff. Most of it is not these presolar grains, the little blobs made in the atmospheres of stars. Most of it's been like reprocessed, like shattered and ground up and reformed into new bits.
Interesting just from like the churning of space, of stuff in space.
Just from the churning of space, it turns out that you can't just hang out as a grain in the middle of space. There are processes happening out there. There are processes that destroy dust and processes that reform it. The dust destroyers that are out there. It sounds like, you know, some big alien ship coming along to clean up the universe, but actually it's shock waves from supernova. When supernova collapse and then explode, they produce these huge shock waves, massive amounts of energy, gamma, rays, neutrinos, all sorts of stuff, and that comes along and it shatters these grains, destroying the dust and breaking it like back down into gas.
Well, you know, they say space is just a big vacuum, so those are just suckle. Anyways, So you were saying that dust is important in the universe. Is it important to the universe or just to our understanding or or to our search for answers about the universe.
Well, both, like the history of dust tells us what's happened out there in the universe. You can take each individual solar grain if it survived this like interstellar shattering process, and some of them have, and you can trace it back to an individual star. Like every star has a different mixture of elements and a different mixture of isotopes, so they leave special fingerprints in their solar grains, and so like ular grain can tell you, like what that star was. It's like a little sample from that star. And some of them are made during supernova and capture elements and isotopes that only exist, we think, in the atmospheres of supernova during those brief moments that are super energetic and can tell us about the formation of heavy elements and what's going on in supernova. So there are these amazing capsules that tell us about the history of the universe.
But I think maybe you don't mean like each individual grain, do you look, You maybe need like a population or like a cloud of this dust to sort of know what the star was like.
Well, each indivi vidual grain tells you something about that star. Not every grain produced by the star is identical, right, and the star has a variety of stuff in it, but each one traces back to an individual.
Star because each grain would be made out of different things.
Yeah, each star would make different kinds of grains. There's going to be some overlap. It's not completely unique, right, But each star is made out of different kinds of stuff, different elements, different mixtures. Each star is a slightly different mass and temperature, and so it produces different mixtures of stuff and different isotopes. So the grains produced by each star are different.
Like an individual grain would have different things in it and different signatures in it.
Yeah, exactly. The isotopes found in an individual grain tell you about the star that it came from.
Mmmm. Interesting. So how is it important to the universe itself? Because it doesn't seem like it weighs a lot in the Milca way. So maybe I wonder if it has a big role in, you know, the dynamics of space.
It does play a big role in the dynamics of space sort of, for two reasons. One is that stuff heavier than gas is the reason that we have like planets and stars and stuff like that. Like the Earth is mostly made out of stuff that's not just hydrogen and helium, right, and that's cosmic dust gathered together to form planets. So most of the rocky stuff of the Solar system came originally from what we would call cosmic dust, right, those heavier elements that are created by stars and spewed out into space. And also we think that this cosmic dust plays a role in the formation of solar systems. You have a huge gas cloud that eventually collapses into a bunch of stars. Why does it collapse. It collapses because it's a little spot here that's denser, that's heavier, that's cosmic dust. Man, Those are like the iron grains and the little bits of heavy elements floating around that seed that gravitational collapse.
Wait, are you saying the Bible was right? We all come from dust, from dust to dust.
And even ashes, right, star ashes cool?
And so then how does it help us study the universe? Or how does it not help us study the universe?
Yeah?
It both hurts our ability to study the universe and helps us. Like it prevents us from seeing things in the universe because it absorbs light and it blocks our view. The center of the Milky Way, which is choked with dust is famously called by astronomers the zone of avoidance because they have to look away from that region. You can't see through the center of the Milky Way in optical lights, so you can't see what's on the other side of the galaxy very easily. So it's sort of a pain for astronomers, but it also captures this history right and in order to understand the cycles of star formation in the universe, we do have to understand the cosmic dust because the cosmic dust plays a role in the formation of those stars and is also then destroyed by the supernovas and then reforms. It's all part of the cycle of the Milky Way. You might imagine the Milky Way is just like a bunch of stars floating in space basically doing nothing, but it's churning and burning. This stuff going on just sort of much longer time scales than we're used to thinking about.
Hmmm, interesting, All right, Well, let's get into how we know where the dust in the universe is and the very important question where does it all comes from? Who's making this mess in the universe. So let's stick into that. But first let's take a quick break.
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All right, we're talking about cosmic dust, which is not a drug, I imagine, so it sounds like it might be something you could sell on the streets.
I don't know. If you walk down the street in Berkeley and you ask people for cosmic dust, I'm pretty sure they'll tell you something do.
Sell you something. But we're talking about the dust. It's out there in space between the stars, and it's important because we're all made out of dust. Stars and planets, they're all essentially made come from dust that gravity pulls together, and so it's important for that reason. But it also sort of helps us understand the origins of stars.
In the universe, right, even though it's tiny, it's a little bitty part of the mass budget of the Solar system. It tells us about how things work, and it plays a role in getting those things started.
But I imagine maybe at some point in the universe's history dust It was all dust basically, right, that's where all those stars came from. No, I guess you went from gas to stars and then those made dust exactly.
We think that the universe began and dust lists, right. So it's actually an interesting open question in astronomy right now, is like when was the first dust made? People really want to understand the process by which dust is created and destroyed and helps form new stars, and there's a lot of open questions out there. We don't really fully understand the process of it. But we're pretty sure that the universe began with just hydrogen and helium and the tiny trace elements of things heavier and no larger molecules of course, and it's only when stars began to burn that dust was created.
But I wonder if in the Big Bang, you know, things were so intense, there was so much pressure, there was so much violent processes going on, so many of those that I wondered if some hydrogen started emerging together and make dust without any stars? Is that possible?
What the earliest dust we've seen is like several hundred million years after the Big Bang, and it's possible that hydrogen formed and crystallized somehow earlier on. I don't think we would call that cosmic dust though, if it's just pure hydrogen, probably just call that hydrogen crystals. I think to be called dust probably needs to have some like carbon and some silicon and some heavier elements in it.
But I mean, could a little bit of a carbon and silicon have formed in during the Big Bang?
Big Bang Nuclear synthesis is a pretty precise science, and it tells us based on the temperature and like the cork density, exactly how much of what was made. And we think that it's almost overwhelmingly hydrogen, with just tiny trace elements of helium and then little tiny, anty bitty bits of heavier stuff carbon. Probably not because carbon requires the merging of three helium simultaneously, because lithium is so unstable, so very unlikely that any carbon was formed, but you can't say no, it's possible there were tiny, tiny grains of carbon form during the Big Bang.
So there could be primordial dust out there, like og dust.
That's right. The most ancient dust is possible, though. The oldest dust we've ever seen is a few hundred million years after the Big Bang.
All right, Well, that brings us to our next question, which is how do we know where the dust in the universe is. It doesn't glow in space, right.
It actually kind of does glow in space, not the way that stars do. Right. Stars create their own light through fusion. They light up the whole universe. But everything out there has a temperature, and everything that has a temperature glows. Even the Earth glows, right. It gives off in red radiation, and so dust glows in the very very infrared because dust is pretty cold. So you can see the dust if you use telescopes that can see infrared light and so like the Spitzer Space telescope and a James Web Space telescope. These things out there can see dust in our galaxy and in other galaxies by its thermal emissions.
Like I guess you could tell where there was a lot of dust and where there isn't a lot of dust.
Yeah, exactly. You can't see an individual grain, but you can see like huge clouds of dust here and there. You can see it glowing in the very far infrared. You can also see dust by how it blocks light, Like we think we understand how stars glow and the light that they give off, and dust blocks that light. You know, it absorbs some frequencies of it, it reflects other frequencies of it. And so by looking at what astronomers call the extinction curve, like where's light being blocked, they can measure how much dust there is between us and something.
So we measure it by how it much it blocks light, not how much it reflects light.
We measure it by how much it blocks light and also emits a little bit of light in the infrared, So it depends a lot on the frequency it will reflect. Blue light mostly infrared light can mostly pass through dust shorter frequencies where the light has like roughly the wavelength of the dust that will get reflected or absorbed. So when light passes through a dust cloud, it basically gets reddened because the blue light gets reflected and the red light makes it through.
It's a little bit of the opposite of what happens here during the sunset. No, it's the same it's the same.
The light gets reddened, right, the atmosphere tends to reflect blue light, so the sky looks blue because in direct sunlight gets scattered down to your eye. Then at sunset, the light is coming straight at you and the blue light is being reflected away and you're seeing the red light.
It filters like it filters out blue.
Light, exactly, it filters out blue light. And so when astronomers look out into the sky, they can see that some stars appear to be dimmed, and they appear to be dimmed differently across the spectrum. Right, it's not just like the whole star is dimmer, which might mean it just further away, but it's more in the red than in the blue. So these extinction curves are really important for astronomers to study because every time they're looking at something in the universe, they want to know, like how much dust are we looking through? How much is dust distorting what we're seeing?
So technically does that mean that dust this space dust is blue like if you were when you sort of look at it, it's blueish.
I guess it reflects blue light. It glows in the far infrared, but it reflects blue light, so I guess that would make it kind of blue.
Yeah, And have we ever got in a sample of dust, Like, have we ever gone out there and grabbed a vacuumed up some dust to study it.
We do actually have samples of space dust. It's super fascinating. All the dust that we have sampled is only stuff in our solar system, so we've never sampled stuff outside of our solar system. The furthest probes we ever sent had like just barely left the Solar system. But there's plenty of space dust here in our solar system, and many many satellites that we send have little dust collectors. It's kind of a challenge because these satellites are moving in very high speeds relative to the dust, so it can be tricky to like catch the dust. But there are some missions like the star Dust Mission, specifically to capture dust and bring it back. But then lots of other satellites have like a little space dust collector on it. We talked once about the Juno mission that went to Jupiter in twenty eleven had sort of an accidental star dust collector on it. The dust was slamming into the back of the solar panels on the satellite and then spilating off little bits which you got picked up by a camera, and it turned out to be like a huge effective dust collector. And this is how we learned that Mars is giving off all of this dust, which is probably responsible for causing the zodiacal light. We have also captured some dust and brought down to Earth and studied it under a microscope and seen like some fractions of this stuff really are presolar grains, bits of dust that are older than our solar system.
Whoa super old dust.
Super old dust. Our solar system is like four and a half billion years old, But of course stars have been around for much longer than that, and some of them died and created these grains, which amazingly survived out there in space and then formed into asteroids or formed as part of the Earth, or still just floating out there. It's incredible that some of these little grains have lasted so long.
And we also know how much dust is out there because it's polarized, right, it's got some sort of electrical charge list to it.
Yeah, the dust grains are not spherical, right, They have little shapes. They are irregular, which means that they tend to be longer in one direction than another, and because they're made of electromagnetic stuff, sometimes they have an overall charge. You know, the dust like bumps against itself. It gets like static electricity essentially, and then interstellar space it will align with magnetic fields. You know, the Earth has a magnetic field, the Sun has a magnetic field, the whole galaxy has magnetic fields. We think there might even be magnetic fields out there in between superclusters. We talked ones about primordial magnetic fields. Anyway, the dust grains are a great way to measure those magnetic fields because they align with the magnetic fields. And then when light passes through them, it tends to polarize the light because the dust itself is pointing in a specific direction. So light passing through this region can tell you about the dust and about the magnetic fields in that region. It's sort of an amazing way to learn about these huge regions of space which otherwise look empty.
Well, it's like having special glasses to see the universe.
Yeah, exactly. So we have lots of ways to study cosmic dust and to look at the spectrum, and you know, looking at the spectrum also tells you what's in there because if it has like a certain crystal, then that crystal has rotational and vibrational frequencies and they will absorb with those frequencies or emit it those frequencies. And so they can tell what's in cosmic dust even if we can't sample it, Like cosmic dust is far far away in the Milky Way. They can tell what it's made out of based on how it glows and how it absorbs light.
Mmm, because that can change, I guess, depending on what was happening there that made the.
Dust exactly, because cosmic dust is not static, right. One of the big mysteries is like where's all this cosmic dust come from? And you know, we think that a lot of it is made in stars. It's made in supernova It's made in these stars called asymptotic giant branch stars. It's made in super red giant stars. They have like just the right conditions in their atmosphere to coalesce this stuff, like outflowing and cooling gases will create these greens and shoot them out into the universe. And that's cool, but it can't explain all the dust that we see out there. There's like not enough stars and not enough formation of this dust to explain all the dust that's out there in the universe, because, as we said earlier, the dust doesn't survive forever. Right, the dust is like shattered by supernova. So we have like stars pumping dust out in the universe, supernova shattering right back in the gas. And that leaves sort of a mystery because there's not enough being made by the stars to explain all the stuff that we see out there, all the dust in the milky.
Way I see. So like dust is sort of like they're bigger molecules basically, right, they're like little tiny pebbles, and inside of the stars they just burn up I guess, right, because it's so hot and under so much pressure.
Yeah, that's why they're made. Like in the outer atmosphere, the outflowing and cooling gases coalesced into these grains. If that ever happened inside the star, that would just burn up as fuel.
Yeah, like the carbon and all the silicon. It's sort of gassy within the sun, but once it gets out of the sun, it tends to form into molecules and maybe little clumps mm hmm. But then you're saying, like, once it's out there, in space. Then if there's a supernova, the supernova breaks it up back into carbon and silicon exactly.
So like the typical lifetime for a grain of dust, it's like one hundred million years. It can float out there, and then on average it's going to get shattered after about one hundred million years, some longer, some shorter, but on average one hundred million years.
There are that many supernovas happening to shatter. It does so frequently.
There are not that many supernovas, but they're frequent enough and powerful enough to shatter this cosmic dust.
So like on average, for any point in space, you experience this shattering supernova every hundred million years.
Yeah, the supernova are more common than every hundred million years. There's a supernova in our galaxy roughly every fifty years, So in one hundred million years, you're going to get two million supernova across the galaxy and they're very, very powerful. So the modeling at least tells astronomers that these things should be shattered on average within one hundred million years.
But the Earth has been around longer than that, and have we experienced such as shattering supernova.
The Earth has been around much longer than that, but it would take a very close by supernova to shatter the Earth. These grains are more delicate than the Earth, which has been like compressed.
Right, So like if there's a bit of dust circling the Earth, it would get shattered by the supernova, but not our atmosphere or us.
Yeah, dust is more fragile, you know, it's floating out there into space, is very low pressure. These things are sort of fragile compared to life a rock on Earth, all.
Right, So then the mystery you're saying is like how it's made?
Then, Yeah, the mystery is like why is there still so much of it? There's a lot more cosmic dust out there than can be explained by this combination of stars producing it and then supernova's destroying it. There's a lot more cosmic dust that can be explained by just that process.
Maybe the unergy hasn't bought that neat device you have to get rid of dust.
Well, one theory about what's going on is that cosmic dust itself can reform out there between the stars. So you take these little pebbles, these little grains, you send them out there. They get shattered back into gas. But there's like a tiny little seed left, you know, a few molecules still cleaning together, and then those can accrete because they're flowing through these molecular clouds which are super duper cold, and basically because you have a few tiny little grains left, they can like pick up more like ice can form on these things, and you get these layers that surround the original tiny core that rebuilds this thing back up into what you would call dust.
I see, yeah, just reforms could because and also because of gravity. I imagine, right, like even if you split a little grain of dust out there, eventually gravity is going to put it back together, isn't it.
Yeah exactly? And you know that's the process that eventually forms stars and plants, right, These little gravitational seeds gathered together over very long periods, but it begins with gathering little bits of ice here and there and reforming. And so some of the cognic dust that's out there are like og grains that came from their stars and haven't been shattered, but most of it probably comes from this process where they have been shattered and then they coalesce, collecting ice and reforming into grains.
All right, Well, you mentioned that there are some things called dust destroyers out there in space, and also mysterious ways that dust is made, and so let's dig deeper into those things. But first, let's take a quick break.
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Okay, we're talking about dust and Daniel, you're saying, the big question is where does it come from? Because most of the dust, if you just put dust out there in space, within one hundred million years, some distant supernova's shockwave is gonna shatter that back into its constituent atoms like carbon and silogan. It doesn't seem that fragile here on Earth, right, Like if I blow on dust, it doesn't break up into carbon gas.
I mean, you're pretty tough, dude, But are you saying that your breath is as powerful as a supernova?
Well, some mornings, yeah, But I mean, like it's weird to think that it's so powerful because here on Earth we don't feel these supernovas. But you're saying it's strong enough to like split apart molecules in space.
The dust is more fragile than the Earth is. Yeah, and it hasn't been a supernova in our Milky Way in quite a few hundred years, so it's not like we're feeling these things every ten years or so. Even these supernovas are not that common. But yeah, the lifetime of dust is shorter than the lifetime of the Earth, so the Earth and planets and stars definitely survive these super nova shock waves in ways that the stellar dust doesn't.
So then the mystery is, like, if it is being destroyed out there in space, why is there still dust? Why isn't it augies gas and individual atoms.
Exactly, And it's important that the dust is there because the dust seeds planetary formation and star formation, you know, in ways that we didn't always understand. Like back in the seventies, before we really understood cosmic dust at all, people thought that our solar system started just from gas, that you could start from just like a blob of hydrogen and helium and form all of this stuff, which doesn't really make sense to me because then like where you're getting all the iron and all the stuff to make planets. But now it's very well understood that most of the iron and most of the heavy metals are bound up in these cosmic dust grains and you need them to form solar systems with interesting bits on them, like rocks and people.
So then are you saying that like just gravity, you know, pulling all of this stuff out there floating in space into dust is not enough to account for the dust we're seeing. Well why not?
So just stellar production of dust isn't enough to account for the dust that we're seeing. You need some way to reform dust in the interstellar medium, Otherwise, as you say, it would be just gas. But we think that these little grains probably do gather back together from gravity and from just secretion of ice crystals. As you pass through a molecular cloud, there's gonna be chemical bonds that form because these things are a little sticky, right, And so that is a process that they think might explain where the gas comes from. I talked to one scientist at the University of Wasda in Japan who's super interested in cosmic dust, and she said that this is like the leading theory for how cosmic dust is being regenerated. But nobody's like demonstrated this in the lab. They haven't done tests where they take like a little grain and pass it through a dust cloud and see this stuff reform. It's alsort of like theoretical chemistry at this point.
Well, you need to replicate zero gravity, wouldn't.
You, Yeah, exactly. It's the kind of experiment you'd want to do out in space or on the iss or something.
So then that's the best answer to this mystery.
That's the best answer to this mystery.
So it sounds like you're saying, like there's a giant vacuum in space's gathering all this stuff dust.
Well you know again it's the supernova, right, those are the dust stories shattering it back in to gas. And then they think that it's probably reforming. But another really fascinating way that they're trying to understand this process is by trying to answer a related question, which is like how early did dust form in the universe. So now that we have like a super powerful infrared telescope, we can look deeper into the history of the universe and look for evidence of dust very very early on, like what is the oldest dust that we can see in the universe, And they'll give us a sense for these processes because remember, like stars didn't turn on for a few hundred million years, so the origin of the dust can really tell us about like who is making this dust?
Right I think I mean like if you look out into deep space with your telescopes, you're looking back in time, so like the light you're getting from those deep places in the universe is really old light, which might be old dust exactly.
And we think that most of the dust out there in the universe right now is probably produced by these super red giant stars and this asymptotic giant branch stars. These special stars are super big and it just right conditions for this, like outflowing gas to cool and form these little blobs which then flow down into space. But the James Web Space Telescope recently saw a direct evidence for really really old grains of stars, like several hundred million years or up to a billion years after the Big Bang, too long ago for these stars, Like, we don't think that there were these super red giant stars early on in the universe. So probably the first dust made in the universe were made by supernova from the first generation of stars.
Whoa wait, so how do we know we're looking at does that old?
Because we're looking at images of galaxies that are super duper far away, And so you can look at a galaxy and you can understand from its red shift how fast it's moving away from us, and therefore how far away it is, and therefore the age of the thing we're.
Looking at isn't most of that light coming from the stars in the galaxy.
Yeah, most of that light does come from the stars, but we're looking at the infrared telescope and stars are much quieter in the infrared, so we're seeing information from the dust also.
Oh, I see, like we see the galaxy with regular light and then we switch the filter over to infrared, and then you're basically getting the light from the dust.
Exactly, and specifically, what they're seeing here is extinction, right, They're seeing an absorption feature at a very specific wavelength twenty one seventy five inkstrums that they think is like a dust wavelength. That that's what dust absorbs. So they see like a dip in the light in this galaxy at just the right wavelength that tells them that there's dust in this very very old galaxy.
Oh, because I guess the size of your thing affects what kind of light you're absorbing, right, because you kind of have to be at about the same size as the wavelength to absorb it exactly.
Earlier we were talking about how dust absorbs. That's various frequencies. In general, the picture is that it interacts more with blue light. It reflects that blue light and it doesn't interact as much with reddor light because, as you say, it's too small, like the wavelength of light is bigger than these dust grains, so it doesn't interact with them. But also these things contain specific chemicals and sometimes little crystals, and those have features that absorb at certain wavelengths, like little oscillations and vibrational energy levels of these little crystals inside these dust grains will absorb at specific wavelengths that are known to be dust wavelengths. So they saw this in this signature from the James Web Space telescope from the super duper Ancient galaxy, a galaxy too old to hold any of these red giant stars or ASB stars. So they think probably this is ancient dust, maybe from the first round of generation of dust in the universe, probably from supernova.
Like the first supernovas, right, because that's that's when the heavier elements are made.
And it's fascinating because supernova make this stuff and then also destroy it, so they kind of like clean up after themselves.
Right, Wait, how can it make them and destroy them at the same time.
These dust greens are made by supernovas sort of in the last dying minutes of a star's life, where you know, these shockwaves create really intense environments and specific isotopes, and then the out flow and the cooling makes these grains. But then shockwaves from supernova's also destroy dust. Right, supernova are the dust destroyers of the universe, So they both create it and they also are responsible for destroying it.
Which do they do first? Do they first clean up and then put a bunch of dust there or do they put a bunch of dust and then immediately destroyed It can't be the latter, can it, because then we wouldn't have any dust.
It must be that the shockwave from the supernova travels out faster than dust grains, which means the first they're cleaning up and then they're making a mess. So I guess you're right. Actually it's in the wrong order. Or they're destroying the dust grains from other supernovas and to make space for their own.
So they're not cleaning up after themselves. They're just cleaning it so that they can make a mess.
Yeah, they're sort of like scrubbing the graffiti off the wall and then writing their own name on it.
Yeah, I take it back.
I take it back. Everything positive, I said about.
Supernovas, well, they're the reason we're here. So glad they haven't wiped us off, I guess, and we're glad that they made us all right, Well, what does it all mean about our understanding of the history of the universe.
It means that all these processes, the ones that form stars, that lead to supernovas, that lead to dust creation and dust destruction, it's all part of this huge cosmic dance. You know. We tend to think of the Milky Way as like done, We've made all these stars. They're just sort of like hanging out and burning now. But it's a process, you know, and everything is connected as like dust flowing and swirling. These things are being created, they're being destroyed, they're being reformed. The whole thing is a big, frothing, active, lively mess of processes, all of which are important to creating the universe as we know it.
Yeah, and it sounds kind of precarious, right, Like, basically, we need a supernova to make all this dust, and we need the dust to basically clump together into planets and stars quickly before the next supernova tries to wipe the board clean, right, Like if another supernova had gone off near us, or not even neuros, but around us. Before the Sun, you know, got put together and the Earth got put together, we might not be here. Is that true?
It definitely would have affected things, but it's not something we understand very well. And supernovas contribute in lots of different ways. Like first of all, they destroy these grains, but then later on a supernova shockwave can actually precipitate the gravitational collapse of surviving grains into a new star. So supernova shockwaves play lots of different complex roles. And to say like that we even understand this story would be to overstate it. For sure, there's a lot of parts of this that we still don't understand. What we do know is that it's complicated and everything is connected.
Sounds like our knowledge of it is a little dust.
There's definitely a lot of ancient wisdom out there we haven't yet collected, and we can look forward to blowing the dust off of all of these secrets.
But not too hard, because then you might destroy the dust.
Right, only if you have supernova morning breath.
All right, I guess the next time you look at into the nice sky, I know that you're looking at a bunch of dust as well, not just the beautiful twinkling stars.
These tiny but mighty grains play an important role in the formation of the solar system, in helping us understand what's out there, and also in blocking our view of part of the glorious cosmos.
You hope you enjoyed that. Thanks for joining us. See you next time. Hey, it's hore Hey from the podcast, and I'm super excited to announce that my new book, Oliver's Great Big Universe, is available to order now.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact, but the people in the dairy industry are. They're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases, many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
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