Nic: 

This is episode two of season two of the Meridian. It is March 11th, 2022 and we are once again coming to you from Lund Observatory, Lund University in southern Sweden. 

Crossing our local Meridian today we have Diane Feuller who is a researcher here at Lund Observatory working on galactic archaeology using stellar abundances, ages and kinematics. This season we are also bringing you some field reporting from the Nordic Optical Telescope on La Palma. 

It is not easy to observe with an active volcano covering everything with ash and lava, but more about that later. 

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The intro scene includes background music and 24 high school students saying astronomical words like “Space missions”,  "Solar wind", "The big dipper", "Galactic dynamics", "Gravitational waves", "Exoplanets", "Black holes", "Betelgeuse", "Dark energy", "Near earth asteroids", "Jupiter", "Ground based telescopes" and more.  Slowly it fades to everyone saying “The Meridian”.      

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Nic: 

Hey Rebecca. 

Rebecca: 

Hi Nic. 

Nic: 

You look a little tired, are you alright? 

Rebecca: 

Wow, isn't that obvious? I actually. You know, I actually ran in today. I'm I'm actually happy I don't have a car 'cause – Have you seen the fuel prices? 

Nic: 

I have seen the fuel prices. 

Rebecca: 

You know good thing then that you can either bike or actually run to work. 

Nic: 

You didn't bike? 

Rebecca: 

I actually ran today. 

Nic: 

You ran to work! 

Rebecca: 

I wanted to try if I could do it. It's a downhill to Lund. 

Nic: 

OK, that's really impressive, how far will the run have been? 

Rebecca: 

15K or so? I don't want to go next to the car road. 

Nic: 

Yeah, right still 15K is... you know I can barely walk 1K !  But what are we gonna talk about today? 

Rebecca: 

I thought we could talk a little bit about Pluto. 

Nic: 

OK. 

Rebecca: 

Yeah, it feels like it is always showing up in the debate. Should Pluto really be a planet? It's classified as a dwarf planet now and it's something that people get very emotional and sometimes actually upset about. 

Nic: 

So how do you feel about it? 

Rebecca: 

Thing is, I guess Pluto has a bit of a weird history. You know, it was discovered fairly late compared to the other planets, so 1930, but it was discovered by the Americans and I think there's some sort of patriotic feeling to it. Perhaps that they want it to be a planet because it's the planet that they discovered. 

Nic: 

Right, everyone wants to have a claim to a planet discovery, and then it maybe got classified a little bit quickly before we really were in our where we really defined our planets. 

Rebecca: 

Yeah, yeah, I guess. 

Nic: 

So I guess what are some of the problems though that we sort of have with calling it a planet. 

Rebecca: 

As they say, it was discovered like in 1930s, so this is almost 100 years ago. But then it was not untill the late 70s, I think, that they discovered one of its moons, Charon, they could calculate its size and they realise that. Whoops, it's actually not that big. 

Nic: 

Yeah, so I think what people don't know is the Pluto's orbit is pretty far out and there are actually a lot of other bodies out there that are orbiting and we have just started to be better at seeing those and we're seeing that they're the same size. 

Nic: 

So many Pluto was the first of these bodies that we saw, and you know.  Time sort of tells, because we have discovered a lot more.   

Like Make make, Haumea.... 

Rebecca: 

Ceres, Sedna.  They're all dwarf planets.  And some of these are comparable in size to Pluto. 

Nic: 

Yeah, right? 

Like I remember growing up as a little kid, I had a song for learning all the planets. These songs are going to go on for ages.  You have to be singing for an hour, and then I'll probably be out of breath and pass out. 

So, so that is an issue, right, you know, and so it also dilutes what actually a planet might be. 

Rebecca: 

I understand you.  But even so, when I think about the solar system, planets in my head, I go all the way to Pluto. It's still part of my planet vocabulary as such. 

Nic: 

Yeah, exactly. And even like the moons of our solar system are actually larger, like you have Ganymede, Titan, Callisto and even Triton on Neptune. And actually the moon is also bigger than Pluto as well, so it's yeah. 

Rebecca: 

Right so I guess the field sort of came into this like tricky concept of what you would really classify Pluto as, since there are other bodies that are clearly not planets. 

Nic: 

Yeah, exactly. 

Rebecca: 

We couldn't call the moon a planet, right? And so it, together with a lot of other bodies, was classified as a dwarf planet. And as you say, it's discovered by Americans, and I guess this is like a very emotional thing for some Americans to be honest, I don't really care, but I also have this idea. I guess that... Why should something that's classified as a dwarf planet be, you know, valued less than a planet? 

Like I've studied both like giant stars and dwarf stars, and it's not like in our field that we're like, oh dwarf stars. They're like not as good as giant stars. We don't make that distinction. 

Nic: 

Yeah, well, even dwarf stars are usually what we are looking at when we want to look for habitable planets currently because they're like not easy to observe. 

But we also have, if you go into a higher scale, we have dwarf galaxies which are much smaller than the Milky Way and Andromeda as well. There are quite a few that orbit the Milky Way, like we have the Draco Galaxy.  And also in the Southern hemisphere we have the Small Magellanic Cloud and the Large Magellanic Cloud. 

Rebecca: 

Right?  So it goes to show that it's easier for nature to create smaller things.  We have more dwarf planets. 

We have like 70% of all stars are M-drawfs, and we have more dwarf galaxies than we have spiral galaxies.  It's more common to have these, and they're actually extremely interesting. 

Nic: 

Yeah, exactly.  I know, for example, dwarf galaxies act as building blocks of larger galaxies with simulations and stuff. So like, just because something is giving this dwarf tile, that does not make it scientifically uninteresting. In fact, it could be the opposite case is that it's actually more interesting 'cause we want to know well how do you get from this dwarf case to some of the bigger things that we see. 

Rebecca: 

Yeah, and I guess.  Also you shouldn't really get your emotions into dictating our science. 

Nic: 

Yeah, exactly, that's a dark road can follow down. 

Rebecca: 

Yeah, but I actually thought we could - speaking of dwarf galaxies - talk a little bit with our researcher here, Diane, who actually works with dwarf galaxies quite a bit. 

Nic: 

Oh yeah, OK looking forward to that. 

Rebecca: 

Yes, let's invite her. 

 

---------------------- Scene change with music.     

 

Rebecca: 

And now I'd like to welcome to the mic our very own researcher here DIane Feuller, Welcome. 

Diane: 

Thanks. Nice to be here. 

Rebecca: 

Yeah, and thank you for coming on our pod.  So happy to have you. So I want to sort of go right into it. When I've been talking to you like in the hallways, here you talk about galactic archaeology, but what is that really? 

Diane: 

Yeah, it can be a little confusing.  So normal archaeology is the study of like past human life and cultures on Earth, and they study it through the materials left behind. 

So in galactic archaeology the materials that are left behind from the past activity are the stars. So in galactic archaeology we use stars to then see what we can learn about what happened in the Milky Way in the past. 

Rebecca: 

That's quite cool. 

Diane: 

Yeah, so the stars actually hold a lot of information about the influences that a Galaxy has gone through in its life. And we see these in the metals that are in the star. 

Rebecca: 

OK, so well - metals?  

For our listeners might not know this terminology. What do you mean with metal? Is it like iron? 

Diane: 

Right. In astronomy metals are basically anything that's heavier... Any element that's heavier than helium, so typically.... 

Rebecca: 

So basically everything. 

Diane: 

Yeah, basically everything, and often we talk about the overall metallicity and that usually refers specifically to iron, but then we can look in more detail at the individual elements which are formed through different processes and they can tell us a lot more about what happened in. 

Rebecca: 

The past sure, how did you come into studying this subject? 

Diane: 

Well, it's really just sort of a happenstance of who you work with and who is at the institution you study at. 

When I was in undergraduate, the professor that I worked with studied star clusters, and so I did a little bit of work on star clusters, and then when I moved on to Graduate School to get my PhD, there was someone there working on galactic archaeology with this brand new survey called Apogee and so I got to get started with that new survey, and basically just stars sounded interesting to me and so that's how it happened. 

Rebecca: 

Right, it sounds like stars are fossils in a way. 

Diane: 

Right, yeah? So each generation of stars basically creates more metals in a Galaxy, and so when a new generation of stars forms, it's affected by all those previous generations. 

And when we observe a star - in the spectrum of a star we can measure the amount of each element that is at the surface of the star, and that is basically a preserved fingerprint of the composition of the gas when the star was formed. 

Rebecca: 

OK, so you know, looking at these elements and what have you learned so far, like what do we know of the history of the Milky Way, has this always looked the way it looks like now with a spiral arms or? 

Diane: 

It's complicated, but we can actually learn a lot through just looking at the stars.  The main tools that we use are both the elemental abundances of the star, so the exact composition, how much of each element is in the star and also the kinematics of the star. 

Rebecca: 

Kinematics? 

Diane: 

Right, so how the stars are moving throughout the Galaxy in our Milky Way Galaxy. It basically has three main cellar structures, so we have the disc of the Milky Way, which holds the majority of the stars, and that's sort of shaped like a CD, if people still know what a CD is. 

Then there's the bulge of the Milky Way - this is sort of a smaller sphere of stars that sits right in the middle, and then there's the Halo, which is a more diffuse sphere of stars that sits around the whole, and sort of holds the plane of the disc and the bulge. 

Rebecca: 

OK, do you have a favourite component of those that you study or do you study the whole picture? 

Diane: 

Well, I've mostly studied the disc of the Milky Way, and recently I've been moving more further outwards and studying the Halo. 

Rebecca: 

Is there a reason for it or? 

Diane: 

Yeah, so I started with the disc because it has the most amount of stars.  And you can really learn a lot about the Milky Way with large samples of those stars. 

We sort of expect that a Galaxy that's been left alone... Like I said, each generation of stars creates more metals and puts it out into the Galaxy.  So if you were to line up the amount of metals and a star and of four stars of different ages, you would expect it to be sort of this nice smooth sequence of more metals.  And the stars that were born more recently. 

But if we look at the stars in the Milky Way disc, we see that that isn't really the case. 

We find that there is an old sequence of stars that does follow this nice smooth sequence. However, at some point there's a really substantial disruption in that sequence, which is an indication that some sort of other galaxy came in and collided with the Milky Way, bringing in different stars and new gas. 

And so we see this. There's this disruption. And then afterwards there's a totally separate sequence of stars forming afterwards, so we know that at some point there was a big event in the Milky Way's past that caused this disruption. 

Rebecca: 

Wow, do you know how long ago that was? 

Diane: 

Yeah, we know that it was approximately anywhere from 12 to 8 gigayears ago, so billion years ago. That's relatively early in Milky Way's history because the Milky Way is somewhere between 12 and 13 gigayears old, and so pretty early on. 

But even in that short amount of time, the Milky Way Galaxy was pretty well established already. 

 

 

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