Show Notes

• Sponsor: 8th Light
• Google+: Pamela and Fraser
• Watch the video of this episode as a Google+ Hangout
• Radioisotope Dating
• Radioactive Dating
• Halflife
• Carbon Dating
• Daughter atom : A daugther atom refers to the atom that is the product atom formed during the radioactive decay in a nuclear reaction.
• How Carbon-14 Dating Works — HowStuffWorks
• Protactinium-231
• How Do Geologists Know How Old a Rock is? – Utah Geological Survey
• Methods of Dating the Age of Meteorites
• CosmoQuest
• Moon Mappers
• Lunar Reconnaissance Orbiter mission
• Dawn Mission to Vesta
• How Old is the Sun? — Universe Today
• Gas Chromatography
• WMAP

Transcript: The Ages of Things

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Fraser: Welcome to AstronomyCast, our 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; I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University – Edwardsville. Hi, Pamela. How are you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Good! And where are you this week?

Pamela: I am in Austin, Texas at the 219th meeting of the American Astronomical Society.

Fraser: That’s good. So you are like buried in space news.

Pamela: I am not only buried in space news, but I’m among my people. It’s a good place to be.

Fraser: [laughing] Among your people, right! With your flock – that’s good!

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Fraser: Alright, so this going to be one of those “how we know what we know” kind of shows. How do scientists determine the ages of things? How do we know the age of everything from stone tools to the age of the Earth to the Solar System to the age of the very Universe? Alright, Pamela, so I think that was sort of the plan here, that we’re going to sort of explain to people how we know what are the various measuring sticks – age measuring sticks that astronomers use and scientists use to figure out how old everything is? And I thought, well, why don’t we start kind of close to home and think about, you know, when scientists discover some civilization, they discover stone tools, they find an archaeological dig — how old is everything that was in that dig? How do they know how old that is?

Pamela: It all pretty much boils down to radioisotope dating, and looking to see what’s in what sedimentary layer. One of the things that is a blessing and a curse — and I say curse because it leads to cancer now and then and that’s never a good thing — is a variety of the atoms that get created in supernovae and through other high-energy processes aren’t stable, and they’re not stable on varying time scales, so some things it might be — you set them on the table, and say you have a thousand atoms, well, you wait an hour and you have 500 atoms of what you started with, and 500 atoms is what’s called a daughter material, a daughter atom, and so you can actually look to see how much, what the ratio is between these two different atoms, and based on the ratio, you can see how many half-lives have gone by. Now, if you have something that decays quickly, that’s only good for time dating something in the recent past. I know as a small child, I was nerdy enough that I knew about carbon dating, and I was terrified that my teachers would use the carbon in my pencil to figure out I didn’t do my homework on time because I was that kind of a nerd and lacked the level of understanding I needed.

Fraser: …or you know overestimated the abilities of your teachers.

Pamela: Exactly. Exactly, but the thing is — carbon doesn’t decay on that type of a time scale, so we can only use carbon to date things in the distant past. We can use other forms of dating for the recent past, and through all the different atoms that we have that decay on the time scales of minutes to hours to days to weeks to years to centuries, millennia, to millions of years by combining all of these different types of radioisotope decay, we’re able to very carefully measure the age of different materials that contain these radioactive processes.

Fraser: And so do scientists have these overlapping methods of radioactive decay, and can they go from really, really short events all the way to the age of the Universe? I mean, are there any gaps in this?

Pamela: Well, so in general things that decay quickly are also things that we have to generate in cyclotron laboratories, so it’s not like there’s piles of polonium-120 lying around, so for the most part, the way we get to the things that we can radiocarbon date, and other things like that is we have to go through the archaeological record. So you look for those points where you’re able to bridge from our known understanding of the past of humanity to “A-ha! I found a radioisotope that has decayed in a useful manner,” and from there we just bridge our way backwards. And we do look for the times where we find in materials more than one of these radioisotopes, and just keep building our way backwards.

Fraser: And where does it sort of fall apart? I mean, does each isotope only give you so much, and then it’s just not useful anymore?

Pamela: Yeah, well, it’s a matter of…there’s just not going to have had been enough left at the end of the period. It’s the, well, you go half way to the wall, half way to the wall, half way to the wall, and never actually make it to the wall. At a certain point you have run out of atoms to decay, so you eventually get far enough back in time that the sample you’re looking at has completely decayed into its daughter atoms.

Fraser: Right. And I guess you can imagine, that’s kind of like you’re looking at ice melting. You’ve got a piece of ice on a plate and it’s in the living room, and you look at it and it’s unmelted, and you go “well, that ice was clearly just brought out seconds ago,” and then it’s kind of half-melted and you know it’s been within the last, you know, less than an hour, but more than a couple of minutes, but if it’s just water, it could have been there for a couple of decades.

Pamela: Exactly. Well, not decades, then it evaporates.

Fraser: [laughing] I know — it evaporated. I know, I know, I realized that as I said it. OK, great! So then, which is the tool that they would use? We’re going back to my first example, right? We’re going to take a look at stone tools left by Neanderthals –what is the method that they would use to date that kind of human civilization stuff?

Pamela: So this is where we often use carbon-14. It’s a naturally occurring radioactive form of carbon, and the nice thing about it is human beings tend to pick it up, plants pick it up, all of us…we’re made of carbon, and so we become partly radioactive in the form of carbon-14, and so you can look at the leftover logs in fire pits, you can look at the leftover carbon in the bones and you can start to get at how old things are. carbon-14 has a radioactive half-life of 5730 years, so you can basically step back in these intervals of 1000s of years, tens of 1000s of years…in fact, we think the limit for using this is actually somewhere around 60,000 years in the past that this starts to become a not-entirely-useful way of studying the age of things in our environment.

Fraser: Right. OK, so then you’ve got the quantity of the carbon-14, and then it’s going to… you’re going to be able to measure that ratio of what you had carbon-14 and the various daughter elements that it’s going to decay into, and get a sense of how old it is. OK, so we’ve done, then, carbon-14, and you say that, sort of, how early can we measure with that? Within a few hundred years, right? And then…

Pamela: Well, a few hundred years starts pushing it because you haven’t had that much…I mean, its half life is 5730 years, so a quarter of it will have decayed in 2600 years, and so you want to get closer to the 1000 year mark than the couple-hundred year mark.

Fraser: Right, so definitely 5000 years is great, but you don’t want to be measuring beyond 60,000 years.

Pamela: Yeah, that’s a comfortable place to be.

Fraser: Alright, so the next age of something, I would assume, is going to be like rock formation, lava flows, things here on Earth that we’re going to try and date.

Pamela: So we also look at things like the uranium to thorium dating method, which looks at uranium-234 decaying into thorium- 230 and this is something where we’re looking at processes that, depending on where we are in this, there’s a whole network of things in this that decay. We’re looking for that combination at a half-life of 80,000 years, but we can also look at uranium-235 which decays into the generally-not-talked-about-in-chemistry-class protactinium-231, which has a half-life of 34,000 years, so by looking at these different decay paths and looking at their different daughter processes, this is where we can start getting into more of the geologic record, getting back into the hundreds of thousands of years over the course of their decays.

Fraser: And, same thing if they’re going to measure… I’m trying to think, soil, sediments, or ice cores — things where you’re looking at hundreds of thousands to millions of years old. So you’re telling me there’s little bits of uranium kind of everywhere for the measuring?

Pamela: It’s actually a really good thing because it’s part of what keeps our planet warm. Our planet is a lot warmer than it would be strictly from sunlight hitting it, and an atmosphere that blankets it and keeps some of the IR radiation trapped in. Our planet’s internal temperature is driven by the constant decay of radioactive particles. It provides heat, and that’s a good thing because heat helps to provide life, so be glad for the radioactive materials.

Fraser: Right. So then how, I mean, you keep pushing that further and further back, but I can imagine if the whole surface of the Earth is being re-surfaced (thanks to plate tectonics and such like), that there’d be no way to figure out how old the Earth itself is, and yet we know quite precisely how old the Earth is. So, how did…how on Earth did astronomers figure that one out? Geologists…we’ll let the geologists have that discovery.

Pamela: We do actually look for progressively older and older rocks, and we do find rocks that are billions of years old, and this is where we start pressing ourselves backwards with things like looking at samarium and neodymium, and their decay rates, which get us back to millions of years to now a billion years, so we do have some pretty old rocks, but you’re right — we are pushing the billions of years limit. So we look at sedimentary histories; we look at the way things are capable of moving, and then we start looking at cratering histories on other worlds, and we start grabbing asteroids. Asteroids are really, at the end of the day, the final authority on the original chemistry and the age of our solar system, so we wait for asteroids to actually come to us (we call them meteorites by the time they reach the surface of the planet), and take them to labs, and this is part of why scientists are so avidly collecting meteors, and, well, we know that lots of amateur astronomers are enthusiasts. There’s lots of scientists who would like to take a core sample of that big rock you have found and put on your shelf as a trophy object. That’s actually a piece of data that hasn’t been collected that you’re keeping on your shelf.

Fraser: And so…and so the theory goes that if you’re going to find a meteorite and determine how old that meteorite is, you’re going to know how old the Earth is? I don’t understand.

Pamela: Right. So the idea is the entire Solar System formed at once, and so the age of the Earth is the age of, well, not the Moon — it formed later; it’s a blasted-off piece. So it’s sort of like its materials formed at the same time, but it was part of two other things, but all of the materials came together, maybe not in the same structure they’re in now – big asteroids have broken apart into smaller asteroids, things have hit each other, creating the Earth’s moon, but all of this stuff in our Solar System formed out of the same solar nebula, formed at the same time, and so if you can age a meteorite, you’ve aged the entire Solar System. Now, the more of these that you age at once, it’s like taking more and more measurements. You’re able to get a more and more precise understanding of the age, so this is where we’re constantly trying to catch and collect and understand asteroids.

Fraser: And was this always assumed to be the case, or were astronomers not even really sure that all of the meteorites are the same age?

Pamela: Well, it was one of those things where you postulate it and hope it’s true. And as we’ve measured it, it’s come out to be we’re able to put very good limits on the age of the Solar System using meteorites.

Fraser: Now, you hinted at for a second there that astronomers use cratering on places like the Moon, and I know on Mars and stuff… they’ll use that as a totally different method for determining the age of things.

Pamela: Well, so there’s two different ages that we worry about: one is when did this stuff form, and then the other is when did the surface of the stuff form. So when you look at the Earth, our surface is extremely young; in fact, there are volcanoes if you look at bits of the surface – like Etna’s going…I think earlier this week it went off, and that surface is measured in days in terms of its age. Well, when we look at the Moon and we look at Mars and we look at other rocky surfaces, the only way we have since we can’t readily go there all the time of getting the age of the entirety of the surface is to look at cratering histories. And this is where we actually try and get the public’s help because we want to measure the ages of as much of the surface as possible so we can start understanding what was the collision history in the past, what was the bombardment history in the past, and we create projects that ask you to help us train computers to more effectively measure craters for us because — let’s face it, at the end of the day, measuring craters is fun for a while, and then you want to do other things, but we also ask you to measure craters for us.

Fraser: Right. This is a project that you’re actually working on, right?

Pamela: This is…and you’ve been giving us server advice, so we’re launching a new project called Moon Mappers with CosmoQuest, which Fraser and I have talked about a bit in some of our other hang-outs. CosmoQuest is a community where we’re hoping that you’ll come and learn like you do with AstronomyCast, and listen to Fraser and I, and then apply all these things that you’re learning to actually doing science. And Moon Mappers is our very first science project. It’s part of the Lunar Reconnaissance Orbiter mission (not the orbiter itself), and we’re asking you to help us correct crater finding algorithms, to go in and tell us where does the software screw up, and fix their outputs, and to help us measure the age of various surface features on the Moon.

Fraser: So, this episode of AstronomyCast is brought to you by CosmoQuest. We’re sponsoring ourselves.

Pamela: Something like that. Yeah.

Fraser: Right? But no, I mean, our goal has always been to get everybody involved in space and astronomy to some degree, and we’re trying to…you know, Pamela’s been working with NASA and other science agencies to get data from the spacecraft, and then bring in the general public to help in actually creating science that then gets used for real scientific research that may not even be possible to be done, and so this is one of those projects, and now we’ve got this umbrella organization where we can…and sort of server and hardware and software where we can actually do more and more of this. So hopefully you’ll hear a bunch more of these kinds of announcements and more of these projects as we go on, and we’ll recruit as many as we can to do some real science.

Pamela: And as we move forward doing this, we’re going to be working to determine the ages of different features on the asteroid, Vesta — we’re working with the Dawn mission. On the surface of Mercury we’re working with the Messenger mission, and in all these cases we’re looking for those places that have extremely few craters – those are the young surfaces; we’re looking for those places where you have crater bombarding on top of crater, crater inside of crater, these places that are extremely rich in craters –those are the old places, and then we’re looking to see, “OK, can we trace this area that’s almost devoid of craters, and thus actually trace out where there was a ton of lava from an ancient volcano or a more modern volcano?” We’re trying to understand what was the geologic history? How recently were there volcanoes active on the Moon? That’s something I always am startled by is there was actually volcanism on the Moon. Imagine what that must have looked like to the amoebas swimming around on the planet not paying any attention. It was an amazing past, and we can better understand that past by all working together.

Fraser: But how accurate is this method of determining the cratering? I mean, I’ve heard astronomers say, “Well, you can see that region of the Mars is a billion years old,” or “This part is very active and is about a million years old,” but how can we know that this amount of craters is a billion, and that amount of craters is a million?

Pamela: Yeah. It gets tricky, especially since the cratering rate isn’t constant with time. And we don’t know how it varied with time, and so right now what we do is we bridge together the different periods using actually Moon rocks. So the astronauts when they went to the Moon, and the spacecraft (mostly Russian) when they went to the Moon and brought back rocks, they brought back rocks from a variety of different terrains. They brought it back from nice, young areas; they brought them back from older areas, and with each of these rocks using the radioisotope method, we were able to determine, “This area with this cratering rate is this age; this other area with this other cratering rate is this other age.” Now, the problem that we run into is we’ve only done these sample return missions for the Moon. We want to do them for Mars. This is part of the plan for Mars MAX-C mission that’s planned for the next decade. We want to do this with asteroids, and right now we’re sort of making assumptions. We’re saying, “OK, so we think some things happened earlier on Mars — it’s further out. Some things happened later for Mercury — it’s further in.” So we’re making rough corrections to what we know based on the Moon, based on theoretical models, but for the most part we’re within a few hundred million years, which isn’t entirely a comfortable place to be, but that’s the best we can do until we bring back enough rocks to say, “OK, this type of terrain is this. Period. We’re done for the entire Solar System.”

Fraser: Right. I can see that part of the process is that the astronomers have…they’ve got pretty accurate measurements on the Moon, and they’ve been able to sort of correlate the cratering with the Moon rocks that they’re bringing back, but then they’re taking that cratering estimate and using that as a measuring stick for other parts of the Solar System, but they haven’t backed it up yet with actual samples, which is, you know, hopefully going to come within the next few decades. OK, alright, so that’s enough sort of stuff in our Solar System. Well, I guess there’s one more object in our Solar System we should probably take a look, and that’s the age of the Sun, but obviously we can grab parts of the Sun.

Pamela: No. [laughing] That would be dangerous.

Fraser: …and we’re making a pretty big assumption that the Sun formed at the same time as the planets in the Solar System. So how do astronomers know this?

Pamela: Well, so at a certain point, we do assume the Sun formed at the exact same time as everything else in the Solar System, but moving beyond that, we also look at stellar evolutionary theory models, where we say, “OK, the Sun is this size, it had to go through this in the past, it took it this long to get to the stage it’s at now.” So that’s one way of doing it, and then, where we can, we also use, well, in this case instead of radioisotope dating, we call it cosmo-chromatography, and this is where we actually use the exact same idea, but with different types of elements. For instance, strontium is one that gets used when we look at…or scandium are elements that get used when we start looking at stars and figuring out, “well, how old is that?” So there’s a whole variety of isotopic combinations that can get us gigayears of age.

Fraser: Right, but we can’t take, again, a piece of those distant stars, stick them in our gas chromatograph and get the age. Like, what is the method that they use to determine even just the chemical elements in the stars? How do they do that?

Pamela: So the nice thing is the Sun is actually in some ways a gas chromatograph for us. One way you can determine the composition of things here on Earth is you burn them, and you look and see what emission lines are present in the heated up materials, and you create spectra and use the spectra to get at the composition. Well, the Sun you don’t exactly need to set on fire — it’s kind of already there, so when we look at the Sun, all of the atoms in our outer atmosphere, depending on the exact energies, are either emitting wavelengths of light that we can see as spectra emission lights, or much more commonly, they’re sitting there absorbing out radiation and creating atomic absorption lines, and by measuring the depth of these absorption lines (do they absorb all the radiation in a given wavelength of light? Do they absorb just a little bit of light in a given wavelength?), by looking at the depth of the lines, it tells us how much light has been absorbed and a variety of other things, like what are the ratios at different temperatures? We can get at the temperature of the star, and then we can get at the surface gravity of the star, and then we can get at the abundance of materials within the star. Unfortunately, it’s a three- variable problem, and you have to solve for all three variables, which can get really annoying, but when you’re done you know exactly what a star is made of.

Fraser: And so by, again, measuring the ratios of those various elements, which are known to decay at very specific rates, you can determine how old that star is.

Pamela: Exactly, so here we again still use uranium, in this case, we’re looking at uranium-238, which has a half-life of 4.47 billion years, and it decays into lead-206. We’re also looking at rubidium, which has a 48-gigayear life. We’re looking at aluminum, which has a .75-megayear half-life. So we have all these different atoms that we look at, and by looking at all these different combinations, we’re able to fine tune to get a good sense of how old things are. Now the only problem with this is you have to be able to get extremely high-resolution spectra to see all these different lines, and to get high-resolution spectra you are somewhat confined to only looking at the brightest stars, and to a certain degree, only using the biggest telescopes, so it limits how far away you’re able to use this method.

Fraser: OK, fine. How do astronomers know how old the Universe itself is? You know? Cause, I mean, you can’t go and grab pieces of Universe stuff at the Big Bang, you know, and measure its age, so that’s gotta be the final, ultimate challenge. How on Earth, do…how on Earth, how on Earth do astronomers determine just how old the Universe itself is?

Pamela: Well, for the Universe in general, because that’s such a controversial number in so many ways, we need to have multiple lines of evidence. So the first thing, we say no star is allowed to be older than the Universe — that would just be silly.

Fraser: That’s fair.

Pamela: Yeah, so we just look at the oldest stars and use stellar evolutionary theory models, and we’re able to figure out from the cooling of white dwarves, from how long it takes stars of different masses to become red giants, that globular clusters, which are the oldest collections of stars in the Universe are 12 billion years old, give or take. So we know the Universe is more than 12 billion years from looking at the stars, and then beyond that, we have to start looking at cosmological models and matching the predictions of those models to what we see when we examine the cosmic microwave background, and the evolution of structure in the Universe, and from the using the WMAP (the Wilkinson Microwave Anisotropy Probe), we’re able to study what was the distribution of hot spots and what was their size on the cosmic microwave background radiation, and we’ve done entire shows on this so you should go back and listen to those.

Fraser: …one whole episode on just how old the Universe is.

Pamela: Yeah, so go back and listen to that, but it boils down to a whole lot of scary, complicated math (and geometry, more to the point), that tells us that our Universe is more than 13 billion years old. So the stars and all of the fancy calculations using the cosmic microwave background all get us to the same place — and it’s all consistent with what we see from radioisotope dating.

Fraser: And now we have that really precise, precise number. I mean, now we know it’s 13.75 (plus or minus .17) billion years old.

Pamela: Yes, and they just keep adding new decimal points; the accuracy just keeps getting better.

Fraser: As successive versions of these surveys of the microwave background radiation come out with more sensitive instruments, they’ll just keep adding decimal places, but we’re pretty confident with the 13.7 part.

Pamela: Yeah.

Fraser: That’s really cool.

Pamela: So we live in an old universe on a fairly young planet, and we’re still at the beginning of the Universe, but we’re at the most interesting time. And so all these techniques have ganged up to give us a consistent result, and we’ll continue to work into the future, and it’s just one of those neat things to see the pieces building together.

Fraser: Sounds great! Alright. Well, thanks a lot, Pamela.

Pamela: My pleasure.

Shownotes

This week’s special guest:

• Chris Lintott
• Oxford Astrophysics
• Galaxy Zoo
• BBC’s Sky At Night

• First moments of the Universe – NASA
• Molecular hydrogen – Wiki
• Protogalaxies — Wiki
• Abstract:  Molecular Abundance Ratios as a Tracer of Accelerated Collapse in Regions of High-Mass Star Formation – Lintott, et al.
• Abstract:  Molecular signature of star formation at high redshifts — Lintott, et al.
• Paper:  Population III Stars and the First Protogalaxies — LANL
• First Stars — Universe Today
• Young stars and carbon monoxide in the early universe – Universe Today
• Millimeter Astronomy – U of Arizona
• Submillimeter Astronomy -  U of Arizona
• Molecular clouds and star formation — Powerpoint from ESO
• Cosmic Dust — Wiki
• Comet research (water to Earth?)– NASA
• Chirality — Wiki
• Circular Polarization of light (light with magic powers)– Wiki
• Deuterium -- Science World
• VLA — Very Large Array
• James Clerk Maxwell Telescope
• Caltech’s Submillimeter Observatory
• Smithsonian Submillimeter Arrary
• Interferometry
  
• ALMA Telescope
• Chajnantor, the high plateau of Chile and site of ALMA

Transcript: Molecules in Space

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Dr. Pamela Gay: With me this week is Dr. Chris Lintott of Oxford Astrophysics.

Dr. Chris Lintott: Hi, how are you doing?

Pamela: I’m doing well. This is a fabulous adventure this week. I’m here without Fraser and hopefully one of these days I’ll get him over here. But luckily, Chris has agreed to join in this week and talk a little bit about things that he knows a lot more about than I do.

This week we’re going to talk about Molecules in Space. From the first Stars to the newest Planets, Molecules and the Chemistry that allows them to form affect all aspects of Astronomy. While most Astronomers group all Atoms into three bins of Hydrogen, Helium and everything else, there are a few who do proper Chemistry.

They study the sometimes Complex Molecules that formed between the Stars. Let’s start by going back to the beginning to the first moments of the Universe where Hydrogen, Helium and trace amounts of Lithium and Beryllium were all we had. Back in those early moments, where did Molecules mix into everything?

Dr. Lintott: Well at first glance it all seems rather boring. Physicists love the start of the Universe. You can solve the equations on the back of a beer mat if you know what you’re doing. Everything is simple as you say you’ve only got to worry about Hydrogen and Helium.

But even here we should think about Chemistry as well. There’s only one Molecule of any importance and it’s the most common in the Universe right from the beginning to today and that is molecular Hydrogen. Page 2, two Protons stuck together.

Now why do we care whether there’s molecular Hydrogen or atomic Hydrogen? It turns out that right in the beginning it’s the molecular Hydrogen that lets you form the first Stars. You see what you have within the first Proto-Galaxies are large clouds of hot gas. To form a Star you need to get that gas to collapse under its own Gravity.

To do that, you’re fighting against the random motions of the particles in the gas. The hotter the gas the faster those motions the harder it is for Gravity to get anything to collapse. Once you form molecular Hydrogen though, Molecules of it are radiating. They radiate away energy.

Pamela: They give up their heat.

Dr. Lintott: They absolutely do that. So once you form the molecular Hydrogen, you can cause a cloud of gas to cool to a critical temperature where it can collapse to form a Star. The only problem is molecular Hydrogen is not very good at cooling things down to anything less than a few thousand degrees.

So, it’s that temperature that sets the size of the first Stars. In fact we believe the first Stars must have been about a hundred times the mass of the Sun, really big behemoths that marked the beginning of the Universe.

Pamela: Now Stars are quite large objects and they’re quite hot objects, why does it need any cooling at all to take place?

Dr. Lintott: Well just the Gravity is quite weak. So trying to form a dense clump of material ONLY using Gravity means you better get rid of all other Forces otherwise it will be overwhelmed. So you need to cool it down to stop, to slow down these random motions to enable Gravity to win.

We see that if you go into the present day where are we forming Stars? We’re forming Stars within Nebulae, within cold, dark regions of the Universe, probably with in just a few degrees of absolute zero. Not out in the sunlight lit by all the other Stars of the Galaxy.

Pamela: So this is even where Pervnert, our first semester Chemistry equation comes into play. If you heat the gas up too much you have too high a velocity and everything tries to expand away against the fight of Gravity essentially.

Dr. Lintott: Sure.

Pamela: So we get Stars forming, what are the first Molecules we want beyond H₂ to start cropping up with the mixture?

Dr. Lintott: We’ll ignore the minor stuff – Lithium Hydride is very exciting [Laughter] for those who study Lithium Hydride. It’s Lithium plus a Proton. With apologies to them, we’ll leave that alone.

Things get really exciting once we’ve moved on to the second generation of Stars. This first generation lives fast, dies young, will explode in just a few million years seeds the Cosmax with what we call metals – Carbon, Oxygen, Nitrogen – all the interesting Elements.

If you look around the Universe today the thing you see most of is a familiar molecule: Carbon-Monoxide. We see this almost everywhere that there is dense gas. It forms from collisions between Molecules. Actually it turns out to be quite useful because we can see it a long way away.

We can see emission in either the millimeter – short-wave radio – or even the sub millimeter – very short-wave region of the spectrum you see out. There’s a very tight correlation between the amount of Carbon-Monoxide in a Galaxy and the rate at which that Galaxy is forming Stars.

So by doing a survey of Galaxies in this otherwise obscure Molecule, we can work out the Star formation rate. We can see how many Suns are being born in each Galaxy. The remarkable thing is that this relationship holds over many orders of magnitude.

So whether you’re looking at a gas cloud in our Galaxy and you want to know how many Stars are forming or whether you’re looking at a Starburst Galaxy that’s forming 50 Suns a year.

Pamela: Now just to clarify is it the actual amount of the Carbon-Monoxide in the Galaxy or the strength of the Carbon-Monoxide lines in the Spectra?

Dr. Lintott: Given enough hand-waving, the two are the same. [Laughter] The hand-waving is where the art of all this comes in. For example you have to worry about whether if you have a dense cloud of Carbon-Monoxide you may only see emission from the top layer.

If you’re not careful you neglect the rest of the cloud. But, we’re good enough with this and we’ve studied enough local Galaxies that we can understand what’s going on. So Carbon-Monoxide is the first thing.

If you have a new set of Galaxies like some of the ones we’re following up from my Galaxy Zoo project, the first thing you have to do if you want to do Chemistry is go prove to people that there is Carbon-Monoxide there. Without that you’re not getting time to do anything else.

Pamela: So, once you find the Carbon-Monoxide, what other sorts of Molecules do you find next as you peer through these Star-forming regions?

Dr. Lintott: What we like to do is, you see Carbon-Monoxide whenever there’s even slightly dense gas, but what we’d like to do is home in on the very dense regions where Stars might actually be forming now.

To do that, you look for other Molecules. Molecules that are harder to excite and so only emit significant amount of radiation…

Pamela: Now what do you mean to excite a Molecule?

Dr. Lintott: Oh well to get to what happens to get these to emit the radio waves that we’re seeing, you just bash two Molecules together. That promotes the Electrons in the Molecule up into higher energy levels and then they drop back down and emit the radio waves. So how hard you have to bash the Molecule depends on what type of Molecule it is.

Pamela: What type of densities are we talking about?

Dr. Lintott: Oh well, pretty good laboratory vacuums, all right, [Laughter] a few thousand Molecules per cubic centimeter at the most, at the absolute most.

But nonetheless despite these near vacuum collisions that you see in a typical early Star-forming region – a molecular cloud we call them – will have water, Ammonia, Hydrogen-Cyanide (something I’m particularly interested in), not as a chemical but as a segment of Star formation.

Even things like Ethanol – a Molecule I AM very interested in [Laughter] – which may be familiar to some of your listeners. We see pints of it up in the Orion Nebula and in other nearby Star-forming regions.

Pamela: Now to get those pints however, what size volume of Space are you probing?

Dr. Lintott: Well that’s the thing, what you’re getting at is the – this is a near vacuum – so the idea of doing Chemistry out of a few Molecules per cubic centimeters is ridiculous. If you try and talk to a laboratory Chemist they look at you as if you’re completely insane.

So we have to use the Astronomers’ magic ingredient, which is that we have all the time in the world. Well, not quite all the time in the world but a substantial fraction of time in the Universe.

Pamela: Thirteen point seven plus or minus point 2 billion minus 400,000….

Dr. Lintott: That’s the age of the Universe so we’ll give you that. A typical molecular cloud lifetime is of easily of tens of millions of years. So even if collisions between Atoms say just bringing Carbon and Oxygen together to form Carbon-Monoxide.

Even if the odds are extremely low that the two will ever meet, you have a few million years. You can build up some substantial amounts of all sorts of molecular species. And that’s what we see happening.

Pamela: So we have all of these Molecules popping up. We’re starting to find some rather complex things including the ingredients for some other interesting cocktails. How do scientists study these Molecules? What are they useful for as we’re tracing Star formation?

Dr. Lintott: There are many things. Molecules are the answer to everything [Laughter] and in a very broad sense it’s because suddenly you’ve got a huge amount of information. Say I’m looking at one Proto-Star, a Star that’s just been born. If I’m only a Physicist, if I’m lucky I’ll find out the temperature and the density and maybe the size of that Star. I could go away and build the most complicated computer model in the world to try and understand what’s going on. But I can only match against those three numbers.

But I’m a Chemist as well. I care about the Chemistry. You might see 60 different types of Molecules there and suddenly my model, if it is right, I have to get all 60. So suddenly you’ve got a whole new enormously powerful way of testing your models.

The other thing you can do is these are sensitive to time. Let me tell you a story about how you get the more complicated Molecules. I’ve already said that around Star-forming regions that are cold and dark and in fact it’s so cold that many of the Molecules that we see freeze out we say onto the surface of dust grains.

Pamela: Now you have to stop here and explain what a dust grain is as far as Astronomy…

Dr. Lintott: Think of a sand grain but about a tenth of the size. Primarily Silicon and rather light sand grains themselves or possibly some of graphite-rich carbonaceous compounds.

They’re little particles of not very much formed probably from Super Novae or from the atmospheres of Stars.

Pamela: Stellar ash.

Dr. Lintott: Yeah, we should do a whole show on how dust forms and stuff like that [Laughter] take it for granted that you see these. If you look in the optical (we’ve all seen these images of Nebulae with a region blocked out) you see regions in the Milky Way for example.

The culsac, the stuff running through the Milky Way. So, you have dust and that dust gets coated with ice – water ice, Carbon-Monoxide ice and…

Pamela: This is how actual snowflakes form here on Earth…

Dr. Lintott: Exactly you still need this particle onto which ice can form. In fact something interesting happens. In a catalytic converter in a car that removes all sorts of things from your exhaust, you provide a surface on which reactions can happen.

The dust grains do the same thing. As the Molecules freeze on, they can react with each other. Further complicated Chemistry happens on the dust. But we can’t see anything. We only see Molecules when they’re in the gas not when they’re ice.

But the center of this blob is getting denser and denser surrounded by the ice and suddenly the Star lights up. All the ice sublimates. It returns to the gas state.

We get this really sudden burst of an exotic soup of chemicals called a hot core and then the Chemistry changes very rapidly because it’s not in equilibrium. You just added a whole load of new ingredients to your soup. It takes time for things to settle down.

Pamela: So you’ve basically taken a bunch of frozen ingredients, allowed them to hang out in this dark molecular cloud for awhile, and then you suddenly apply heat. It’s like taking a Bunsen burner to a bunch of ices in a Chemistry lab.

Dr. Lintott: Exactly, so by looking at the chemicals that still exist we can date quite precisely how old a Star is. So we can put Proto-Stars in order of age and begin to understand the process of Stellar evolution.

Pamela: So what sorts of things do you see as these Stars slowly start to light up?

Dr. Lintott: You see all sorts of things. You see the evolution of a complex Chemistry – actually a simpler one – things begin to break down. But you see a very specific Chemistry associated with the disk that remains around lots of these young Stars, the places where Planets are forming.

The Holy Grail I think of Astro-Chemistry would be to find some really quite complicated chemicals in that disk. There are hints, there are models that predict that we should even go so far as have Amino acids the basic building blocks of Proteins in disks around young Stars.

There are a couple of plane detections that they’re there with imagination [Laughter] but I’m sure that very soon we should detect complicated (it’s not life, it’s not even the building blocks of life) but its sounding a bit like Church now. What it may be is the building blocks of the building blocks of life already in place in exactly the right place where the Solar System is forming.

Pamela: We know that there are Amino acids in Space from Meteor evidence. We’re just still struggling to find it out among the Stars.

Dr. Lintott: Sure but there are hints. Well, you mention Meteors so the next thing you’d like to pile on to this tower of speculation that we’re building is that having put the pieces in place in the gas and dust of the disk around a young Star, you’d love to get that material down here on Earth.

After all, we know or we think we know from the Geologists that the early Earth was a dry place. It will have lost all its water…

Pamela: The early Sun was much hotter and it basically would have caused any liquids on the Earth to get evaporated anyway.

Dr. Lintott: Either by the early Sun, that’s one possibility of course, the Earth is a much more violent place. It’s a much hotter body so you need to get water back to the Earth. The suggestion is that Comets brought it here. Just like some people believe Comets have brought water to the South Pole of the Moon that remains there waiting for us to discover it.

Anyway the point is could Comets or Meteors have brought complicated Organic Chemistry down to Earth? It’s an open question. People are doing experiments involving firing things at high velocity to see if the Molecules will survive.

But there is one hint that maybe this is what happened. Complicated Molecules tend to come in two types. They’re called kyroltypes. Think of a Molecule that’s made of the same selection of Atoms but arranged as a mirror-image. They react in very different ways.

I think you can take aspirin, which we all take all the time. But if you take its mirror-image, same Atom, same chemical formula, it’s a poison. So it executes different Chemistry.

The weird thing is that all of life on Earth uses only one set of Molecules. It uses what we call left-handed Molecules, not right-handed ones.

Pamela: And occasionally in laboratories they fight very hard. For instance we have Sugar and we have Splenda. Splenda is just a different way of rearranging the Glucose Molecule.

Dr. Lintott: If you say so. I think we’re still on Sugar over here. [Laughter] But nonetheless, we’d like to explain why life made this choice. Why it didn’t use the full diversity of Molecules available to it.

One solution lies back in the Stars. You see there’s a particular kind of light that comes when you scatter light off dust grains. You end up polarizing light but specifically circularly polarization. It doesn’t really matter what this is.

Think of it as light with special powers if it pleases you [Laughter] the point is this type of light is prevalent. There is lots of scattering of dust around young Stars. We see high percentages of this circularly polarized light.

That selectively destroys left or right-handed Molecules. So you might have your building blocks of light in place, the light from the young Sun may have destroyed all of them that are right-handed and then seed Earth ONLY with left-handed Organic Molecules.

Pamela: Now I’m going to have to make you explain this one a little bit better. Give us a 30-second explanation of circularly polarized light.

Dr. Lintott: Is the answer “NO” acceptable?

Pamela: [Laughter] no, it’s not.

Dr. Lintott: You could think of light as a couple of hours, as an electric field and a magnetic field and they are at right angles to each other. Normally they are oriented in random directions, always at right angles to the direction the light is traveling in.

You can force them if you pass them through polarizing sunglasses for example. You can only let through the light where the electric field lines up in one particular way. That’s linear polarization. That’s why you use sunglasses if you want to reduce the glare on the road because you can exclude the scattered light.

Pamela: And it’s actually quite interesting if you’re looking at asphalt, take your sunglasses off and look through just one lens and rotate the glasses and you’ll see the color of the asphalt change as you’re blocking different directions of polarization.

Dr. Lintott: Sure, we call it tarmac but yes, it’s the same thing. So you can play another trick in a slightly more complicated way. If you scatter off dust in the right way you can select only light where the electric field is rotating clockwise or anti-clockwise.

If you only have clockwise light, If you only have of these types, that’s circular polarization. Confused everyone? I told you just to think of it as light with magic powers. But it gets this way by scattering of dust.

We know there’s lots of dust around young Stars. We know that the Molecules are there. It’s very tempting to put the problem of why life picked only half of the available Molecules back in Space.

Pamela: This leads us to perhaps go so far as to think perhaps there are other Solar Systems that have the opposite-handedness.

Dr. Lintott: Yes it’s certainly a possibility depending on the alignment of that magnetic field and the dust and so on. It’s an interesting thought.

Pamela: And what’s interesting is the Chemistry on Earth is not the same as the Chemistry everywhere in the Universe. Just look at the Deuterium. The ratio of Deuterium that we found here on Earth isn’t the same that you find in other places.

Dr. Lintott: But it’s the same Chemistry. The results are very different. The point is that everyone knows that we’ve all eaten from good cooks and terrible cooks.

So, you can have the same ingredients, you can even follow the same recipe but the results are very different in different circumstances.

Pamela: And it often comes down to the ratios of the ingredient.

Dr. Lintott: Sure. So the point is that we have this universal idea on that. There is a kind of Hydrogen that is Heavy Hydrogen. Normal Hydrogen just has a Proton, a positive particle. Heavy Hydrogen – Deuterium we call it has a Proton and a Neutron. The ratio with the two on Earth is about ten to one.

That set way back at the beginning of the Universe. It’s one of the predictions of the Big Bang Theory that we can sort out this ratio. The weird thing is that when you look at these Star-forming regions that I was talking about before we see a huge percentage of Deuterium, way above Hydrogen. We see chemicals that we don’t see on Earth. And instead of Ammonia being Nitrogen and 3 Hydrogen Atoms, we even see Nitrogen with three Deuterium Atoms in some cases.

So you’re gonna work out why this has happened. The solution is back to the dust grains that we were talking about. It turns out that Molecules with Deuterium instead of Hydrogen don’t stick to the surface of dust grains as well as that Hydrogen-Hydronate.

So when we’re only seeing the gas, you selectively get left with the Heavy Hydrogen, with the Deuterium that’s scattered there. It’s a nice solution to a chemical mystery and it’s good evidence that the dust grains really are playing the roll that we think they are.

Pamela: Then when you melt the ices that are on the dust grains you return to ratios that are similar to what we’re used to experiencing.

Dr. Lintott: Exactly. The hard part is trying to replicate this in the laboratory. There are some wonderful people doing experiments particularly involving understanding how the ices end up on the surface of the dust grains and then how the ice comes back off the dust grains as it is slowly heated.

You’re gonna compromise somewhere. You can produce a laboratory vacuum that’s the same density as Space, so that’s good. You can get the temperatures about right. It’s hard work to get down to 5 Kelvin but you can do it if you need to.

Pamela: How exactly do they work on down to that low?

Dr. Lintott: They use liquid Helium if they have to, but that’s expensive so we go down to liquid Nitrogen temperatures. It’s reasonable you know, minus 70 degrees.

Pamela: It’s like the price of milk actually.

Dr. Lintott: Liquid Nitrogen?

Pamela: Yeah.

Dr. Lintott: But much more fun. What we can’t do is get time. You never get funding to run the laboratory experiment for ten million years.

Pamela: It would be fun to try.

Dr. Lintott: Yeah, and we’d be impatient for the results anyway. You have to compromise some way. You run something at higher temperatures so the reactions happen faster. You run at higher densities.

Nonetheless I think the thing that inspired me to attack this subject was the idea that in a basement in a Chemistry lab in London in my case at University College London, there are people trying to replicate what we see in Space.

This idea of laboratory Astro-Chemistry I think is fascinating. The idea we can build our own, not Stars but at least our own dust grains.

Pamela: Now I can’t end on dust grains. Dust grains aren’t the most exciting thing to me as a Stellar Astronomer out there. I’m more of an observational kind of girl.

As we look out to the future, as we look to try and study the Molecules that are out there in greater and greater detail, what are some of the things that we can look forward to?

Dr. Lintott: There are a couple of really important technological developments that are going to change absolutely everything. The first one is that for years we have suffered the Earth’s sub millimeter. It’s an obscure region at the spectrum, the sub millimeter.

It’s a short-wave radio where all of these molecular signatures are, these fingerprints. The first problem is it’s the same region that water resonates at. In fact this is the kind of frequency that…

Pamela: Atmospheric water actually.

Dr. Lintott: Yeah, well any water. It’s the frequency your microwave works at. Because when you microwave something you’re heating the water in your food. So we can only really do this from very high sites.

Monokea is good for example in Hawaii or a few sites like that. So it’s difficult. There isn’t much other incentive to build a receiver for this unlike Optical Astronomy where everyone has a digital camera now.

Very few people are carrying around their own Heterodyne Receiver with a sub millimeter [Laughter]. I wish they were but there you go. So the point is we’ve been not behind other areas of Astronomy but it’s been difficult to push the technology forward.

Then suddenly we’re about to get handed the world’s largest presents. One is that we’ve always wanted better resolution. With radiant compromises you always end up with you don’t get the beautiful picture. You get a blur across because of the long wavelengths you’re using. The first really big sub millimeter interferometer telescope combines many, many different dishes.

Pamela: Like the VLA

Dr. Lintott: Yeah but for the radio, exactly. We’ve just managed to link together three separate telescopes in Hawaii, the James Clark Maxwell telescope which is a Dutch-Canadian-British institution. It’s the largest dish at these wavelengths fifteen meter dish.

We’ve linked it to Cal-Tech’s sub millimeter telescope just down the road. It is a 12 meter dish so more power there. Then the Smithsonian has a whole array of small dishes. We link those in and they give us the resolution.

I’ve just seen the first science results from this combination of telescopes and it’s like recovering from an operation on your eyes. You suddenly see the Universe in much greater detail.

Pamela: And the way this works is a telescope’s resolution is directly related to how wide the mirror of the receiver of the detector is. In the case of interferometers what matters is what the separation between them is.

Together they end up basically acting as one giant dish. They don’t have the same collecting power but they have the same resolution. The fact that these telescopes are down the road from one another gives you significantly enhanced resolution.

Dr. Lintott: Yeah because you keep the collecting power because we’ve got a 15 meter dish and a 12 meter dish. This is only the starter really. Because in this amazing place in the Atacoma Desert in Chile.

Pamela: Where they measure rainfall in millimeters per year.

Dr. Lintott: Yeah, it snows occasionally, but it almost never rains. I’ve been to this site. The Plain of Trechan which is a fantastic word to say “do you want to have a go?” Are you…

Pamela: No, I

Dr. Lintott: Trakandor It’s fantastic. I’m probably getting it wrong but years of lecturing I’ve just liked proclaiming it. [Laughter] Anyway, it’s this beautiful Plain surrounded by the kind of volcanoes that kids draw. You know, triangular, smoke coming out at the top and lava running down the side.

That’s what this place looks like. Flamingos on the floor of the Salt Lake, the world’s only Lithium mine kind of ruins it a bit. But nonetheless I have to give you a sense of the spectacular landscape. And there is the world’s first truly International telescope.

Everyone has put their eggs in one basket in building a telescope called ALMA. It’s named after the Spanish word for soul for some reason. It’s going to be an array of millimeter and sub millimeter telescopes. About 60 dishes at about 18,000 feet above sea level, up in the high Andes. It’s high enough that it’s dangerous to work up there. The lack of Oxygen gets to you.

So dangerous they’ll be bringing these 12 meter dishes back down the road so they can prepare them closer to sea level before putting them back up. ALMA is going to revolutionize this subject. It comes onstream in about 3 or 4 years time.

The stated goal is to detect Carbon-Monoxide back halfway in an ordinary Galaxy halfway back to the Big Bang. So we have the history of Star formation for the last 6 billion years laid out. We’ll see nearby Galaxies in an unprecedented resolution. We’ll detect Molecules we’ve never seen before.

In fact some people are worried that so many Molecules will be detected that we won’t be able to distinguish the fingerprints, like laying bar codes on top of each other. And ALMA is going to be amazing and I can’t wait to get my hands on it.

Pamela: Well AstronomyCast will still be around we hope and hopefully we’ll be able to interview you when the telescope comes online in the next few years.

Dr. Lintott: Fantastic stuff.

Pamela: It’s been a wonderful interview and I hope to join you again Chris. Thank you.