Dr Ulrike Kuchner University of Nottingham, UK

Dr Kuchner is an astrophysicist working on galactic evolution. she's also an artist working at the intersection of fine art & natural sciences  

Dr Ulrike Kuchner had some 🍸 at the error bar in episode 5 #rod #cone #astro #psycho #chicken #truth

our discussion

welcome to the error bar, would you like to introduce yourself?

my name is Ulrike Kuchner. i am a postdoctoral researcher at the University of Nottingham. i am an astrophysicist, and i study how galaxies evolved in the universe and how the large-scale structure in the universe came to be

i also have a background in fine arts and i make art and curate art in this intersection called art science

great to have you here. do you need a drink?

ooh yes please. we ok with a martini?

martini works

gin martini then

what brings you to the error bar?

well, i hear that really interesting questions are being discussed here, and i am a creature of curiosity

about a year ago i read this tweet from Jim Al-Khalili, a physicist and a science journalist, and he said: 'science tells us there are NO green stars'. and it puzzled me, and i thought 'oh there must be green stars' i thought that was also a psychological question rather than a physics question. i want there to be green stars, so maybe you can tell me why Jim Al-Khalili said there are no green stars?

i like that you want them to be there

well, first of all, it's such a good question, because it sounds really simple, but it's really multi-layered. for the physics layer we can back up a bit and just discuss stars, and the fact that they come in all colours, all kinds of colours, but more precisely from the outer layer of the star. and that is based on its temperature

so it's a really important feature, the colour of the star. we know that bluer stars are hotter and redder stars are colder, for example. so the temperature is related to the kinetic energy, so the motion of the particles and the mass of the star - we really know a lot from the colour

but all objects emit light at all wavelengths, and that is from radio to high energy like x-rays and gamma-rays. but the overall statistical distribution of it, that describes all that light, that's close to this black body curve, which is like a smooth curve that peaks at a certain wavelength, but has a really long tail as well

so for example cool bodies like you and i, we peak in the infra red, but most of the stars like our sun peak in the visible or the optical light. and that also means that we can actually seen them with our eyes - that's the actual issue here

now back to the stars, if we have a reddish star, that distribution of the black body curve peaks in the red area of that distribution, so we see it as reddish. if we go to hotter stars then they become orange and yellow and then white - but not green. and that is because that peak includes what's left and right of it, which is red and blue, and so it's actually a mix of all these three colours and we kind of see this mix as white. and then as it goes even hotter that curve shifts to the blue side, and we see the blueish colours of the really hot, massive stars. i think that is the mystery

well it's disappointing there's no green stars. i found an old book of mine at home and there was this picture of the spectral classes, and they'd use greeny colours to illustrate the spectral classes. do you think it's just a convenient shorthand to say that the middly-ones are sort of greenish

i think perhaps they did this out of simplicity, because this is a complex problem that involves the human biology as well as the physics, so perhaps they just wanted to stick to the one discipline in that book and not make it more complicated

one thing that i will say is that even now we don't have the exact accurate representation in our visualisations. a more precise stellar spectrum template would create a little bit different colour codes which actually shows that there aren't really really red stars, so they are more orangey, yellow, and then kind of like our sun is a white - not yellow - star, and then there's lots of different shades of blue

is it just stars or do whole galaxies or clusters or nebulae, are they green at all? is there any green out there?

yes and no

so, i study galaxies, and galaxies are just made up of many many billions of stars, and since most of the light in a galaxy does come from this population of stars, if most of the stars in there are red then the galaxy will appear red

if we look at the many billions of galaxies out there, we see this bimodality. we have either those red or those blue galaxies, and they tell us about their evolutionary status, and that they're massive, or young or old, and it's really important. and we think that there is an evolution that goes from the blue with the young, massive stars, to the red galaxies that are older and more passive. and as they do this they transition and change their make up. and we call those the 'green valley galaxies'. but they aren't actually green, but they're called green

so the nebulae, etcetera, if you think of these beautiful images where you see a green glowing nebula, that tells us about the composition or the elements in the gas of this nebula. so if it excites in a very specific wavelength that is at the frequency where green is, then this is the actual colour of it, yes. and we tease that out of the image by putting filters on it that are just picking up that narrow wavelength range

when astrophysicists talk about colour, what situations are they really describing? are they talking about on a computer screen or with the naked eye?

we are usually talking about computer screens, or numbers. the images - or spectra for that matter - that are taken by professional astronomers, these are taken in telescopes that are placed in areas where it's very dark, where the air is very calm, no pollution nearby, so these are excellent seeing conditions. in fact, the best is of course to leave the Earth's atmosphere altogether and observe from space

we then put filters that block wavelength ranges and just take the same image through different filters, and that gives us some colour information. so they're broadband filters that reflect these broad green or broad blue light, but there are also these very narrow filters that really look at interesting individual areas where some emission might happen

so a colour is really subtracting one image through one filter by another image through another filter

you talked about atmospheric pollution and getting the best viewing conditions. is that why the stars twinkle?

not just pollution, but because the atmosphere is just not stable. so we have all these layers that are moving, and so the light that comes through it just jiggles and bounces and breaks. and so that's why the single point that should be the star is changing brightness and position very quickly, and so to us that looks like twinkling. so it's pretty annoying

yeah. i was looking at Sirius the other day through my lovely, brand new telescope, and it was definitely orange and blue at the same time. and then i de-focused the telescope, and there was definitely some green shimmering twinkly in there. that's just aberration, or it's like imperfections in everything that's just splitting up the colour, is that?

i'm not so sure about the green twinkle. yes, so i would guess that because you have the optics in your telescope as well, it's all about the imperfections

it seems that you liked it?

yeah, it was quite pretty. it was sort of shimmering and changing colour. it was very nice

there is this phenomenon, the green flash. i have been at the VLT, the very large telescope in Chile, with some staff astronomers there, who were standing outside looking at the sunset: 'is there gonna be the green flash or not?'. so that's a really, i think it's a rare, very brief moment where you have a tiny flash of green, when all the blue and reds are absorbed and not seen

i have not seen one, but i would love to see a green flash

so it's out there?

that is out there, yes. that's when the other wavelengths are blocked, by Earth or by the atmosphere

that's good news

so one problem that your colleague, Dr Meghan Grey pointed out, was that, a lot of astrophysicists are male, and colour deficiency - colour vision deficiency - is more common in men. so how do you as a community get around the problem of having quite a high proportion of people who can't see all the same colours?

yeah, that is an excellent question. it is true that there is a problem in our field, that there's an under-representation of non-males - it's about 20% female currently that have permanent professory positions. is it 10% or so of the male population who are colour blind? in fact, my phd supervisor was colour blind - well he still is colour blind - i guess i was trained to look out for that a bit

it's actually really easy to get around it, but it doesn't happen enough. you can just plot, instead of using colours, use different patterns and labels and shapes. there are wonderful websites out there to help you make your plots colour blind friendly. there are simulators where you can just see what that's like

so i would hope that it's known by now, that we have to take care of this. but it's not as much as it should

can you tell us a bit more about the interface between physics and art. do you think it gives you some advantage in trying to plot, or describe, or perceive the universe?

it's a shame that we have only a few minutes left because i love that topic

the interface between art and science, it's such a big topic, and where to even begin, because they have obviously a relationship to one another, but seem to play these very different roles in our human experience. because we are having such complex problems to solve it's really important to try such trans-disciplinary collaborations. i think important and urgent problems cannot be solved by one discipline alone. like open research is one of them. here the freedom of art and science is really on the line. so these two working together is very powerful

but you actually asked whether you think i have a unique perspective. and, i mean, don't we all have some kind of unique perspective? we all come to creating knowledge with our own historical background, and so mine just happened to be art

and i guess finally, i watched your video - your great video "Do I [dare] disturb the universe?", and you talked in there how you've used errors and mistakes from instruments and cameras to create projects. the error bar loves errors - it's why we're here to talk about mistakes, and what we can learn from them. do you have a view on the role of errors in your work?

i'm thinking a lot about how we respond to errors and uncertainties, and how we deal with mistakes and weaknesses. and also all these images that we create and i talked about a little bit, we try to remove of course the errors. and that makes a lot of sense

but i love the idea of just keeping them as they are. keeping those imperfections and reflect on those. and we try to always find always patterns in the noise and make sense, even if it's just complete, random noise. but if there's a little thing in there that's not supposed to be there, we immediately look at that and 'ooh that is interesting, and that's a little dead pixel in there.' i think it's just giving some space to reflect. and that's what i, that's my favourite kind of art. it's art that invites you to meditate and reflect

but if we know that even the best telescopes and the best instruments make mistakes - and forgive them - maybe we can understand ourselves a little bit better

[🎶 "Sloshed," by Dee Yan-Key 🎶]

any personal errors or mistakes you want to confess to?

oh, loads!

what's your biggest mistake maybe, or your most interesting one?

i don't think i have a good answer for that to get in a podcast

i'm reading and listening to people like, i think it was Neil Gaiman who said: 'make more mistakes, brave, big ones, and embrace them'. i really would like to just stand on a platform and say look at that! i did that

I'm not quite there yet