Nic: 

This is the sixth and last episode of season one of the Meridian. We want to start by thanking everyone who has followed us on this journey into the world of podcasting and we hope to be back soon with the second season. 

Today is the 29th of October, and as always, we're coming to you from Lund Observatory. 

Crossing our local Meridian in this episode we have Paul McMillan, a Milky Way dynamics specialist from the UK who moved to Sweden back in 2014 and who quickly applied for the Swedish citizenship when his home country.. Nah... 

Rebecca: 

You you want to say that he applied for Swedish citizenship? 

Nic: 

Here we go.  Right, and he quickly applied for sweets... Rebecca, can you help me? 

Rebecca: 

Yeah yeah, and he quickly applied for Swedish citizenship when his country decided to leave the EU. 

Nic: 

Thank you.  

Paul is part of the GAIA team here in Lund focusing on galactic stellar dynamics. Later in this episode we will also take a closer look to the skies to find Atlas, not the moon orbiting Saturn.  Or the comet also referred to as C 2019 Y 4 – Phew, that only rolls off the tongue... or the particle detector at CERN.  Or the lunar crater named Atlas and certainly not the titan from the Greek mythology destined to hold up the heavens for eternity.  Imagine having that for a job. 

No, we're looking at the star Atlas and the seller cluster that it belongs to. 

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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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Rebecca: 

Hi Nick,  

Nic: 

Hey Rebecca. 

Rebecca: 

I'm very impressed with you naming Atlas. For that log you barely cached your breath. 

Nic: 

I, I didn't, I almost fainted after saying it. So yeah, thank you. 

Rebecca: 

I look forward to, yeah, getting to know more about Atlas and the stellar clustered it belongs to, so. 

Nic: 

Yeah, it's pretty cool, but I have to point out the elephant in the room. 

The last episode. 

Rebecca: 

Yeah, I know, I know I'm kind of sad in a way. 

Nic: 

Yeah, it's been quite a lot Of fun. 

Rebecca: 

Yeah, right uh, I've enjoyed a lot talking to our guests like all the like astronomers, but also the other guests like Josefin. Jo and Laura. 

Nic: 

Yeah, so we had those three and then we also had Paul, Michiel and Jens. 

Rebecca: 

I hope people also at the department have enjoyed the podcast so much that they want to be on it. 

Nic: 

Yes, definitely. 'cause there are definitely more astronomers that we could interview here.  And maybe sometime, because COVID restrictions are beginning to lift, we might be able to invite a few more researchers to come and talk to us 

Rebecca: 

Yeah, like I really think we need a season two. 

But yeah, before actually you know, going through this episode and interviewing Paul, I was sort of thinking:  what's been happening with you recently? 

Nic: 

So I I just finished writing a bunch of observing proposals with my research group. 

Rebecca: 

All right.  So for telescopes? 

Nic: 

Yeah for the ESO telescopes in Chile. Uhm, yeah, we wrote 10 in total. 

Rebecca: 

Wow, isn't that quite many? 

Nic: 

Yeah, yeah, mostly people, usually will write one. 

Rebecca: 

Yeah, I've written one once and I didn't succeed to be honest, but like there are a fair amount of work you have to do for it.  You know, you need to write your science case and look up the targets. 

Nic: 

A lot of things go into it because, like you know, you say, I want to observe an exoplanet,  for example kelp...  well we can't actually observe Kelp 9 in the Southern hemisphere, but WASP 189 is a target that we're really interested in. 

Rebecca:

Sure. I don't know about these planets. 

Nic:

Oh yeah, so WASP 189 is an ultra hot Jupiter that orbits very very close to its star, so it has a temperature that is almost similar to a lot of smaller dwarf stars at around 2000 Kelvin, it's temperature.  

Rebecca: 

Hot. 

Nic: 

Yea, exactly. And so these things will vary in transient time, so you need to figure out what the best  time is for when you want to observe it and if it's going to be available on the sky, yeah, then I have to also specify of different things like the telescope mode. So I wanted to look at WASP 189 through CRIRES+ which is an infrared spectrograph and it has like... 

Rebecca: 

Sorry. Where is CRIRES on?  Is that on the VLT or? 

Nic: 

Yes, it is on the VLT, yes.  

Rebecca: 

The Very Large Telescope.  Yeah, sorry for interrupting you there. 

Nic: 

No, no, no that's fine.  And it's got so many modes you have to pick the right one that you want to have a look at.  So we're interested in looking at the dynamics of atmospheres. But yeah, basically you start these things off with a brainstorming session of what you really want to see and what is scientifically interesting. And then you go through this process and you help each other. 

You proofread and stuff.  And you go slowly insane, as the you know the hours tick by and you get pizza to come, and it's midnight. 

Rebecca: 

Yeah, I thought you were going to say you go slow and steady but you said you're going slowly, insane. 

Nic:  

Yeah, I think the objective is to go slow and steady, but you tend to descend into a very rapid pace towards the end. So we got our last proposal... 

Rebecca: 

Right?   Oh, so that's why you occupied this room like the last couple of weeks to write those proposals. 

Nic: 

Yeah, we basically lived in this room the entire time, yeah. 

Rebecca: 

That makes sense, that makes sense, yeah, 'cause you still have all of the stuff on the board. It seems like you've been, uh, brain storming a bit. 

Nic:

Yes, yes, that board is burned into my brain right now. I can see it with my eyes closed, but... 

Rebecca: 

Oh, that's really cool. I hope you get time. I really do. Sort of. Yeah, you know, Speaking of the VLT. 

So my research group here actually decided that we're going to be part of this MOONS instrument.  It’s going to be on the next generation of VLT 

Nic:

No. So what does MOONS do? 

Rebecca: 

MOONS is an infrared spectrograph and like it's yeah you know a lot about the infrared, but the sort of main feature that's so nice with infrared is that it penetrates the dust that we have in the Milky Way, and we can sort of see deeper and beyond those cloudy dust parts. 

So what I'm mostly hyped about this is that we will actually sort of penetrate beyond the the middle part of the Milky Way and see, sort of, the backside of it. 

Nic:

Oh wow, so we can actually yeah so the other half. 

Rebecca: 

The other half, so in a way, like, you know when we didn't know what the backside of the Moon looked like, then now we know. And now we probably would the MOONS we’re going to know that. 

Nic:

That's so awesome. So maybe one day we will be able to see almost all the stars in the Milky Way. There's obviously going to be some that are a bit harder to, but you know. 

Rebecca: 

Yeah, of course no. But so I think that's super cool and we will also look at like planets and some extragalactic stuff, but. 

Nic:

Oh, of course, of course, but you know that always gets... 

Rebecca: 

I'm not really as into that.  Then it will of course look at the bulge which is this main part of the Milky Way that I've been researching a lot so I'm super hyped about that. Then the VLT is a great telescope. 

Nic:

Yeah it is. 

Rebecca: 

Yes, I hope you get time on it. 

Nic:

Yeah, I hope so too. But once one of the biggest things about proposal writings is they're really competitive and rejection is very common. So if we do get rejected, that's OK. We'll write more and we'll keep going until we get some data. 

Rebecca: 

And I guess it's still a learning process, right?  

Nic:

It is, yeah. 

Rebecca: 

So so it's not just a waste of time hopefully. 

Nic:

No, exactly and you always get feedback. And also I think it's humbling as well because you know the VLT is a huge telescope and the fact that you can get time on it is still pretty cool, I think. 

Yeah, but there is one other really cool thing I wanted to mention is that I'm actually going observing myself to the Canary Islands in Spain. 

Rebecca: 

You are??  May I guess, the telescope? 

Nic:

Yeah, sure you sure can. 

Nic:

Is it the NOT? 

Nic:

It is the NOT.

Rebecca: 

Ah, that's so cool. 

Nic:

Yes, yeah, too many jokes could get said.  We’re probably going NOT-observing.  We are not NOT-observing if the weather is bad. 

Rebecca: 

But yeah, so sorry.  For all the listeners the NOT is the Nordic Optical Telescope that Sweden was a part of for a long time .  Now, we're not because we're part of the ELT, the Extremely Large Telescope now. 

But me myself, I've been to the NOT twice and it's an amazing telescope, so I'm a bit jealous that you're going there actually. 

Nic:

Yeah, well I would love to have you along with me if I had money. 

Rebeeca:

That's fine. 

Nic: 

We could have done the podcast up on the mountain. 

Rebecca:

But maybe if you bring the mic, you could actually do a podcast from there, like record every evening or something. 

Nic:

You mean like some kind of journal or something like that? 

Rebecca:

Yes, like have a diary from the mountain. 

Nic:

That might be a really cool idea. 

Rebecca:

Yeah, and you know then we have a great reason to have an episode, I mean a season two as well. 
Nic:

Yeah so season two: Reporting my progress on the mountain. I think I can drag Bibi, my PhD Co partner to help me out of it there too. 

Rebecca:

Oh yeah, please. You know you need a co-host . 

Nic: 

Yeah and as one of us is descending into madness, the other one can record that. 
I think that's a ,..

Rebecca:

Oh that sounds amazing. Well I guess before talking about season two we should actually finish and wrap this one up by welcoming Paul to the mic. 

Nic: 

Yeah we should, yeah, and you know, for everyone who's listening, it's been really fun and we really hope that we will come back for a season 2. And yeah, we hope you've enjoyed it. 

Rebecca: 

Yeah, thank you, Nic 

Nic: 

Thank you Rebecca. 

 

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

 

Nic:

All right, and now I'd like to welcome to the mic. Paul McMillan, researcher here at Lund Observatory. Welcome Paul.  

Paul: 

Hey. 

Nic: 

How you going?  

Paul: 

Not too bad. 

Nic: 

Good to hear, so maybe we should get stuck into it. How about you tell us a bit about yourself? How did you end up here in Lund? 

Paul: 

Well, so I'm from the UK originally, and that's where I lived and worked for most of my life. I did my Ph.D. there and I was then working in Oxford, researching astrophysics. 

Uhm, I'd always been kind of interested in astrophysics, and I was good at maths and at a certain point I realised hold on. I can use this being good at maths thing to actually do something interesting like study the stars rather than, you know, become an accountant like my mother.   This seemed like a better option.  

So I was in Oxford researching and as is the way with astrophysicists: The reason I ended up in Lund is 'cause there was a job in Lund that I could apply for.  

And it was one that particularly excited me because what I was working on was the dynamics of galaxies, particularly the dynamics of our Galaxy. How all of the stars within our Galaxy move and what that can can tell us. 

And the reason I'd had that job, the reason why that job had been funded and the reason people were excited by the work I was doing was that there was this mission coming up from the European Space Agency called Gaia. And Gaia was going to be a huge step in mapping the Milky Way and understanding how it's built.  Now Lund is one of the centres of Gaia, it's one of the place where one of its original proposer worked, still works, Lennart Lindegren. 

And the job was to work on Gaia, so that was enormously exciting thing. So yeah, despite my very Englishness. And my caution about leaving a country where I lived my entire life I jumped to the chance. 

Nic:

Yeah, it's interesting. You say your mum is account and count my dad is and accountants.  So do you think there might be some kind of link between, you know, the offspring of an accountant that leads them to astronomy? 

Paul: 

Jumps us into astronomy? I don't know - my brothers. Well, my brother got into computing, another into accountancy and my sister is a biologist, so I don't know...  It's not 100%, I guess.  'Cause one of them could end up in accountancy, but maybe having an older brother who's an astronomer might also push you out of astronomy. I don't know.  It must be complicated. 

Nic:

OK, right? OK, so this might be a cyclical relationship. Going backwards and forwards. 

Paul: 

Yeah, who knows. 

Nic:

That's, uh, that's pretty cool. So you said your, uhm, you work on the Gaia satellite. So the Gaia satellite it was actually something I, well, the data set I use a lot with my own masters research. 

It's got a lot of stars in it, like on the order of how many would you say? 

Paul:

It's got 2 billion stars.  We're, it's slowly increasing over time, but at the moment it's about two billion. 

Nic: 

And how many stars are in the Milky Way? 

Paul: 

So we don't know exactly, because some of them are really faint and some of them are really long way away. And then if you're really faint in a really long way away, we can't see you. 

So we recon it's about 100 billion.  So Gaia sees, you know, a few percent. 

Nic: 

Wow, OK and did any of its predecessors do something similar to what Gaia is doing or like how many..? 

Paul: 

So, there are other surveys that have looked at large numbers of stars, but none that have looked at them with such amazing accuracy.  So the point about Gaia - what makes it so amazing - is that it measures the positions of these stars incredibly accurately. Accuracy equivalent to measuring where something is to within a hair's width:  If that hair is in Paris and you're standing here in Lund.

That's the accuracy we're talking about, and nothing had ever measured anything with that accuracy or anything close to that accuracy. 

The closest equivalent was a satellite called Hipparcos, which flew in the 1990s, nineteen 80s and 1990s, and that only looked at about 100,000 stars. 

So we've gone from 100,000 to 2 billion and we've improved our accuracy by about a factor of a 100, so this was an enormous step. 

Nic:

So that level of accuracy is kind of mind boggling, and I think like you know to anyone listening to you, they wouldn't believe you that you could do that like it's sort of to a hair's width in in Paris. Like how did we achieve that level of accuracy? 

Paul:

Well, the fundamental trick is that almost all telescopes down on Earth, or indeed in space, so Hubble, for example, is a Space Telescope, do measure things to that sort of accuracy. 

But they do it for one patch on the sky.  What Gaia does, is that it does it for the whole sky.  Because it's a really good telescope up in space, not as good as some other telescopes in truth, but it very slowly rotates and takes pictures of the entire sky. In fact, two parts of the sky at a time rotates and covers the whole sky over a period of time.

And it lets you take that image In a way that allows you to piece it all together. 

So the individual images are not extraordinary. They're really not.  They're very much what you get from a good telescope here on Earth. I mean, better than a good amateur telescope, but not as good as the, you know, the top telescopes used by researchers.  

Yeah, it's the fact that you can piece it together across the entire sky. That makes it so extraordinary.  

Nic: 

Uhm, so I guess one of the kind of interesting things we can learn from Gaia.. So they're just tracking the positions and the movements of the stars?  But like, yeah, I guess.. 

Paul: 

So there's a really big reason why that's important, which is that it's very hard to tell how far away something is. 

Not something you always have to worry about when you're on Earth, but we do know... you know, anyone who's been taught this in school or dealt with knows that the reason we have two eyes is that it helps with depth perception and that helps us figure out how far away things are.

When something's far away in space, we can't do the equivalent of that necessarily. We can't take two pictures of it at once and use those two together to work out how far away something is. But what we can do is take two pictures at different parts of the year. 

The Earth moves around the Sun, so you've got two pictures taken at different times, and the star seems to have moved on the sky. 

Just because your telescopes has moved. The Earth has moved. Gaia has moved.  And that lets you work out how far away a star is, and otherwise you really can't do that because you don't know how you can see how bright it looks to you, but you don't know how bright it is intrinsically necessarily. 

Uhm, so there's no other way of directly measuring the distance to a star, and that's why everyone was so excited about Gaia, because until you know, the distance to a star, you really don't know much about it. 

You don't know how bright it really is. You don't really know what's going on with it, so that's the biggest most exciting thing of all. 

Nic:

Yes, and that that phenomena is the parallax effect.  

Paul: 

That is what it's called. Yeah 

Nic: 

Right OK cool. Uhm so I guess.. Is that one of the biggest reasons why Gaia is ground breaking or is there other reasons too? There's like, well, like about other hidden things within Gaia that can really... 

Paul:

It is a Swiss army knife thing. It does all sorts of different things. The incredible accurate positioning is a big part of it. 

And that gives you parallaxes, so distances to stars and it also gives you what are called proper motions, which tells you how fast the star is moving across the sky. 

Because you know that will tell you about how far the star is moving, sort of, perpendicular to your line of sight. Across the sky.   So that's great, but at the same time you're measuring the brightness' of these stars as they appear to us with extraordinary accuracy. 

Which you can do, again, for all of these two billion stars in a way that you couldn't do from Earth because there's no atmosphere in the way. It's a spacecraft, so you get these incredibly accurate measures of its brightness and its colour. 

And and for a decent fraction of these stars, a few percent, not all, but a good few percent you get spectra of the stars, taken on board the satellite, and with those spectra you can figure out how fast the star is moving towards or away from you, which otherwise you can't. Using the Doppler effect, which just shifts the wavelength of the light that you're seeing by an amount that depends on how fast the star is moving towards or away from you. 

And you can measure the properties of the star as well.  Its chemistry.  The chemistry of its atmosphere, what its made of.  How much iron is in the star and some other measures of what chemicals are in there.

What elements specifically are in the atmosphere of the star, which tells you something about what elements were in the star when it was born. 

Nic: 

Right. Have you found any weird stars? 

Paul: 

Yes, definitely there's 2 billion. There's a lot of weird ones in there. One of the hardest problems is weeding out what's a weird star and what's just something weird that happened to your data, so you don't neccessarely know.  

One really exciting one that had been found before, but was not neccesseraly understood.  Noone quite knew what it was, is an object called a Thorne-Zytkow object. 

A Thorne-Zytkow object is bizarre.  A Thorne-Zytkow object is not a star. It is 2 stars. 
Nic: 

Oh  

Paul: 

It is a neutron star at the heart of a red giant star. These are hypothesised. These have been thought of, and there are ways that you might expect to know these things are these things, and that includes two main properties that they have to have. 

They have to be incredibly bright because that increases their brightness and you have to have some measure of the certain chemicals in the atmosphere of the star. 

People had already measured the chemicals in the atmosphere of the star and thought, ‘well, hold on. This looks like a Thorne-Zytkow object, but we don't know how far away is.’ 

That's where Gaia comes in.  

So this was actually the first paper I ever wrote using Gaia data. The day after the first major Gaia data relate, myself and Ross Church, who is another researcher here in Lund Observatory, looked at this one star.  

Looked at, actually it's proper motion rather than its parallax, and we're able to work out that. Yes, this star is really, really far away, so it probably is a Thorne-Zytkow object.  It probably is a neutron star at the heart of the red giant. 

Nic: 

So it's kind of like a Jaffa of a star, like, I've got an outer layer of a bigger star and a chocolaty neutron in the centre. Or is it a binary system. 

Paul:

See yeah it's one big star. It's a small star inside a big star. It's very it's very much just one thing.

Nic: 

OK, well then he said that was your first project that you worked on. What are you working on at the moment? 

Paul: 

As is often the life of research about a number of things, but the one that's got me most excited is related to something we saw in the the last data released from Gaia. 

What we did was we looked at the movement of stars in the outer parts of the disc of our Galaxy, so we looked at those stars and we said - Well, we don't have line of sight velocities for these stars. We don't have the radial velocities of these stars

Well, we have it for a few, but most of them are too faint to get that. But we do have what Gaia gives us so well: Their distances, their parallax and their proper motions, so their movements. 

Nic:

Right.

Paul:

So we know a bit about how they're moving, and from that we were able to show - for the first time - that stars in the outer galaxy, stars in the outer part of the disc of our Galaxy, aren't all moving in a sort of smooth group.  

You would expect them all to have a roughly consistent, sort of, set of motions.  You know it varies, but they're all sort of rotating around a certain average speed, and they're moving up or moving down, or more likely neither moving up or down on average, but staying steady. What we found was, when we looked there, that there's a group of stars rotating fast and moving upwards, and a group of stars rotating slow but moving downwards. 

Nic: 

Oh, OK. 

Paul:

And people had looked in this part of the Galaxy before. We weren't completely new to this, but what they'd always done, as far as I can tell, is taking averages of the velocities of these stars. So what you see is on average, just somewhere in the middle. 

Whereas because we had so many more stars we could work with, because there's so many stars seen by Gaia, we could actually say Oh no, if you look at this, there's one clump here, and one clump there.  What's going on with that? 

So that was very exciting and led to that question I just asked: What's going on with that? So that's what I'm working on now. 

Because my first love in astronomy was making models of galaxies and trying to understand galaxies before I got into dealing with the data on them. 

So, so we've been making models looking at what happens if you take a disc Galaxy like the Milky Way.   And a small satellite Galaxy plunges past it and shakes it.  And what happens, it turns out, can be exactly what I just described,  

So we reckon we've figured it out now. 

Nic: 

How did you see those two populations? 'Cause you said everyone just automatically goes and takes an average. So what did you do differently that allowed you to split those two populations? 

Paul:

So it was very much just having enough stars that we'd observed that we could take the data and really plot out the distribution.  We could make a plot of their velocity going around the Galaxy and their velocity going upwards and downwards in the Galaxy and we have for relatively small area in the outer Galaxy we could do that for tens of thousands, hundreds of thousands of stars. 

Other people just didn't have that much data available to them, so they'd if they tried to do this what they would have seen is not enough to say anything really. It would have been too confused to do that.   Too little data to say anything. 

So because we had so much data we could plot out the diagrams of the two velocities and go: Well what's going on here?

And our first answer was, well, something is probably wrong here, we've probably done something wrong.   But that is the way with any discovery in astrophysics.  It's automatically your first assumption.

Nic: 

It's generally a rule. I live by every morning, so definitely. 

Paul: 

Yeah exactly. Most discoveries start with someone going “well that can't be right. I must have made a mistake”.  Of course, most mistakes also have that happening, so it's very hard to tell which ones going on as it happens. 

Nic: 

Sure

Paul:

So yeah, we went away, did lots of maths to make sure we got it right.  Talked to everyone I was working with and got them to check.  So yea, that's how it happened. We saw this thing we desperately tried to explain why we weren't seeing this thing and it was actually a mistake we've made. And at a certain point we had to accept that we got it right.  

Nic: 

Yeah, that's it's cool that you can actually plot things out and sort of see things with your eyes still and like it's just the idea that we're still in the act of measuring things. And there's like there's still this kind of idea that you need that scientist intuition to build a picture of what you're looking at… 

Paul:

A friend of mine who I will credit so I'm not stealing his idea called Ralph Kenrick has made the analogy that at the moment when we look at the Milky Way, we're looking... We’re like scientists when they first had good microscopes. And we look at what appears to be a completely nothing thing and you see bacteria wriggling around and you identify them and draw them and see them. And that's the stage we're at. We're finally at the stage where we can do that. 

Their next stage then is OK. Now I need a theory of bacteria. Now I need a theory of germs. Now I need a theory of the Milky Way, so that's where we're heading. 

Nic:

So is there another mission that's going to supersede Gaia? Or is Gaia perfect? Is it going to answer all our questions in astronomy and we don't need another. 

Paul:

Gaia is as near to perfect as... hehe, no. That's that's not entirely fair.  

So there is always hope for a future mission and we are in the planning stages of one that I very very sincerely hope we'll be able to have in the future at the moment is just called Gaia-near-infrared, but I think we'll go beyond that name fairly soon to something a bit more original.  

The idea of it being basically twofold.  Gaia looks at stars in optical light, so the light we can see with our eyes and that's fine, and that's great and that's very, very useful. But there are big parts of our Galaxy, especially towards its centre, which is dusty. 

Just just so full of dust that has been thrown up by stars as a part of their life cycle that that blocks out the light of the stars, and this includes the Galactic Centre, which is a very exciting place to look. 

That blocks all of the optical light, but if you go to longer wavelengths, if you go to infrared radiation then you can see through the dust because the dust blocks bluer light, optical light and it doesn't block infrared. So that's the idea that a future emission would be able to look into those areas as well, by looking in the infrared and so explore these dark, unvisited territories of the Milky Way. 

Yeah, so so that's the that's the exciting next step. A few months ago ESA, the European Space Agency had one of their big planning documents released called Voyage 2050, and this idea was recognised as one of the big themes that they want to go towards. So this is, this is something that we've been leading here in Lund, again. David Hobbs who is our deputy head of department. Has been leading this white paper and is leading this charge and so we're very excited about that as our big next step. 

Nic: 

Yeah, will that give this a similar amount of stars like on the order of a billion or will that do more? 

Paul:

More, for sure. How many more, we’re still in the early planning stages, but maybe a factor of five more, I don't. I don't think we'll get quite the level of jump that we got between Hipparcos and Gaia.  The big reason for which is that Hipparchos existed before the age of CCD's, the kind we now have every digital camera.

So having them in Gaia was what made it possible to go from Hipparcos to Gaia. 

Nic: 

I've always a kind of personal question. I've been wondering: Is there a limit to how many stars we could map like is there if, say, is there like enough... Could you see to the other side of our Galaxy or is there, like you know, do you think there's a fraction of the stars that we'll never see in the Milky Way.  

Paul: 

It gets harder and harder, but there's nothing that makes it impossible at any point. 

Uhm, with the sole exception of, I suppose if there's another star in front of the star you're interested in, that one would probably be impossible. 

Yeah, but even then it will eventually they'll move, so wait long enough and that won't be true anymore.  

I don't think there's a theoretical maximum other than, well: There's a theoretical maximum to the number of stars that we can observe in our Galaxy, which is the number of stars in our Galaxy. 

But we're already looking at other galaxies with Gaia.  The large and Small Magellanic Clouds, which are satellite galaxies of the Milky Way have millions of stars mapped and even Andromeda, M31, the nearest Milky Way-like Galaxy we have, we were able to map the bright stars in Andromeda with Gaia. 

Nic: 

Thats, that's cool. And then many more for a more fun question, do you have a favourite object or it could be star?   Or you said dwarf galaxies, which I know do exist in the Gaia dataset that you have, that exists in Gaia. 

Paul: 

So my research tends to be sort of on the big scales. It's the whole Galaxy. I make models of the whole thing or large parts of it so probably my favourite part would be not related to my own work, but  is in the Gaia data set. It's a star whose name I won't try to repeat because its SMS J and then a very large number. 

And if you looked at it, it would look like quite a boring star.  It's towards the centre of our Galaxy. It's you know, fairly bright, but not extraordinarily bright. And if you take a spectrum of it, you really don't see anything. There's not a lot there. 

But that's what makes it exciting. There are almost no elements heavier than hydrogen or helium.  Metals as we call them, as astronomers call them.  In this star there's about 1 - 10 thousandth as much metals in this star than there are in the Sun.  

It's extraordinarily metal-poor, as we call it. 

And it's sits.... it's living in the middle of our Galaxy at the moment, and it's on an orbit that's not taking it very far from the centre of our Galaxy. 

And Gaia data is how we know that last part, by the way, 'cause Gaia measured its velocity across the sky. 

So that's all very exciting and you put those two things together. You get that piece of information. There's two pieces of information together that's telling you that this is an incredibly old star. In fact, we believe it's the oldest star we've ever seen.  

Nic: 

Oh wow. 

Paul:

Because the very oldest stars didn't... There weren't a lot of elements heavier than hydrogen and helium available for it, and they were formed in...   

Star formation started at the centre of our Galaxy and then spread outwards.  So you put the fact that it’s mettal poor and the fact that it’s at the centre of our Galaxy together. You've got the fact that it must be an incredibly old star, probably from a couple of 100,000,000 years after the formation of the Universe itself.  

Nic: 

Wow, OK.  

And that is one of the reasons I love this star.  The second is that my wife discovered it. 

Nic: 

Oh wow. OK,  

My whife is called Louise Howes, she works under that name, she is now Louise McMillan and she was a post-doctoral researcher here in Lund, that's how we meet, and a part of her PhD project she published a Nature paper which was the discovery of this star.
The discovery of this oldest star we know of in our galaxy.

Nic: 

Uhm, this has been really, really cool to hear you talk about Gaia and it's a fascinating instrument. I just want to say thank you so much for being on the podcast and crossing our Meridian. Yeah, it's been an absolute pleasure.  

Paul: 

Thank you very much. Thank you for having me. 

 

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Rebecca: 

Looking through our telescopes we can observe and study the Universe we live in.  We see quasars, protoplanetary disks, variable stars and much much more. 

Today we would like to spend a few minutes taking a closer look at one of the many wonders of the Universe.  Here to assist us we have Katrin Ros, the editor of the magazine Populär Astronomi.   

I would like to welcome you here Katrin. 

Katrin: 

Thank you so much Rebecca. 

Rebecca:

So please tell us what's captured your interest today? 

 
Katrin: 

 So as this is the last episode, I picked a winter object that is kind of fun to look at through a small telescope or binoculars, so the Pleiades. 

Rebecca:

Right, so yeah. What is the Pleiades?  

Katrin: 

So it's an open cluster.  It's like a region in the sky of stars that has been created together. So in the case of this open cluster, it's very young. 

Rebecca:

Is that why we can see it or? 

Katrin: 

Uh, we can see it because it has very many or several massive stars. 

Rebecca:

Right, and they're brighter, so that's where we can see them. 

Katrin: 

Yeah, exactly.  So it's a cluster of like thousands of stars actually, but most of them are very, very dim, so we see seven of the stars actually with the with the naked eye. 

Rebecca: 

Right?  OK yeah 'cause I I think I know which one you're talking about 'cause in the sky I usually... When I was a kid, I called it like the small Big Dipper because I think it looks like a very small Big Dipper, but I've heard it's for some people. It's a bit fuzzy, but you say that you can see the seven stars. 

Katrin: 

Yeah, well, OK. I'm one of the people for whom it is a bit fuzzy. So I've never seen small, small Big Dipper.  

I see a fuzzy spot, but you can actually see seven of the stars, and if you take just the normal binoculars you can see even more. So that's kind of cool to look at actually. 

Rebecca:

Oh, that's cool and I guess one of the stars in in here are called Atlas, because that is what Nic mentioned in the beginning. 

Katrin: 

Yea, exactly.  So one is called Atlas and all these seven ones we can see have names. Actually, there are others.  They’re called Electra and Maya and yeah. 

Rebecca: 

Right, OK, but as we said, we expected find about 1000 stars in there. 

Katrin: 

There yeah, exactly exactly, but most of them are so dim. 

Rebecca: 

OK, do you know what distance it is to the cluster? 

Katrin: 

Uh, yeah, so it's about 440 light years.  We actually didn't know this for a long time. 

It was complicated, but now with Gaia we have determined this pretty well. So 440 light years, that's like 100 times as far as the distance to the closest star from Earth. 

Rebecca: 

OK, so it's like it's fairly close but not super close. 

Katrin: 

Yeah, exactly. 

Rebecca:

Right, Do you know how we find it on the sky. I said it's like for me it looks like a small Big Dipper but what, sort of, do you go for when you want to find it? 

Katrin: 

 Yeah, so you can find the constellation of Orion.  And if you follow Orion's belt, the three stars there in the middle, and you follow them up right for a little while up in the sky.  Past the brightest star in Taurus, if you know what if you know that one otherwise just follow Orion's belt for a while and then you will see like a fuzzy spot, for most people, yeah. 

Rebecca:

Right, so that would be the Pleiades.  

Is it also called the Pleiades in Swedish? 

Katrin: 

No in Swedish, it's actually called Sjustjärnorna, so seven stars. 

Rebecca:

Oh OK, that makes sense. 

Katrin: 

And,  in Japanese it's called Subaru. 

Rebecca:

Oh like the car? 

Katrin: 

Yeah, exactly exactly. 

So both the car and there is a telescope as well in Mauna Kea in Hawaii that is named after this cluster actually. 

Rebecca:

Oh, that's cool. So in a way, it's a famous cluster.  

Katrin: 

It is. It is  

Rebecca: 

OK. I really encourage everyone listening to this too, yeah, if you have a pair of binoculars to go out and try to find it, it's I think it's very beautiful to look at. 

And yeah, with that, I'd like to thank you, Katrin. 

Katrin: 

Thank you, Rebecca 

Rebecca: 

And to close this season. Thank you everyone for listening. 

 

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Rebecca: 

The sixth and actually last episode of the first season of the Meridian was hosted by Nicholas Borsato and me Rebecca Forsberg. 

Our guest today were Paul McMillan and Katrin Ros, and our producer was Anna Arnadottir. If you have any comments or questions about the show, then feel free to reach out to us via our emails or via the @LundObservatory account on Twitter. 

In our theme at the beginning of the show, we could hear members of the 2021 Astronomic Youth Research School, which was held here in Lund back in July. 

The music is called Twilight and was composed by Stellardrone. 

This was the final episode of season one. If you missed any of our episodes, you can of course find them on www dot.... Oh, Nic, can you just come and help me with the last one? 

Nic: 

Fair enough, it was, uh, www.astro.lu.se/TheMeridian 

Rebecca: 

Ah yes, thank you. 

Nic: 

No worries. 

Rebecca: 

And also thank you for all of you guys who've been listening to us and we wish you clear skies. 

Nic: 

It's been an absolute pleasure. 

Rebecca: 

Yeah, and thank you, Nic. 

Nic: 

Hey thank you Rebecca.