NATURE PODCAST

Podcast: Bird colour perception, terraforming Mars, and attributing extreme weather

Hear the latest science news, brought to you by Ellie Mackay and Adam Levy.

This week, how a bird sees colour, modifying Mars, and linking extreme weather to our changing climate.

In this episode:

00:54 Modifying Mars’s atmosphere

A lack of carbon dioxide might hamper efforts to make the Red Planet habitable. Research Paper: Jakosky & Edwards

08:52 How discerning zebra finches discern colour

New research shows that female zebra finches can differentiate orange from red. Research paper: Caves et al.

15:09 Research Highlights

A dinosaur with giant feet, and record breaking nanoparticles. Research Highlight: A dinosaur that stomped the Jurassic scene on size XXXXL feet; Research Highlight: Pirouetting particles twirl at one billion times a second

16:47 Linking extreme weather to climate change

Researchers are working on systems to rapidly attribute extreme weather events to climate change. News Feature: Droughts, heatwaves and floods: How to tell when climate change is to blame

23:30 News Chat

Evidence of a liquid lake on Mars, and using a giant black hole to test a gravitational phenomenon. News: There’s water on Mars! Signs of buried lake tantalize scientists; News: Milky Way’s black hole provides long-sought test of Einstein’s general relativity

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Transcript

This week, how a bird sees colour, modifying Mars, and linking extreme weather to our changing climate.

Nature Podcast

Introduction

This is a transcript of the 2nd August 2018 edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (http://www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to podcast@nature.com.

[Jingle]

Host: Adam Levy

Welcome back to the Nature Podcast. This week, we’ll be taking a peek at how zebra finches see colour, and we’ll be hearing about a problem with plans to terraform Mars.

Host: Ellie Mackay

Plus, we’re learning how researchers are linking individual extreme weather events to climate change. I’m Ellie Mackay.

Host: Adam Levy

And I’m Adam Levy.

[Jingle]

Interviewer: Ellie Mackay

First up this week: have you ever thought about living on Mars? Right now, it’s not the most inviting environment. But there have been plenty of ideas about how that might be changed. Here’s Bruce Jakosky – he’s one of the authors of a paper in Nature Astronomy this week, and he’s been looking at how realistic some of these ideas might be.

Interviewee: Bruce Jakosky

Right now, the average temperature at the surface of Mars is about -60 °C, and if we could raise it up to 0 °C, then we could have liquid water. That would allow us to function as humans in the environment without the need for domes or habitats.

Interviewer: Ellie Mackay

Bruce is talking about the concept of terraforming Mars – modifying the atmosphere to make the planet more Earth-like, and therefore habitable. But it’s not just the temperature that’s an issue. For us to live there, the atmospheric pressure of Mars would need to be 150 times greater than it is today. Yet proposals to terraform Mars have become increasingly popular. I asked Bruce how realistic the concept of terraforming Mars actually is.

Interviewee: Bruce Jakosky

What you can’t see is that I’m smiling at that question, because the less we know about how we would actually terraform Mars, the easier we think it is, and as you begin to explore it, it gets harder and harder. Right now, it’s in the realm of science fiction because we don’t really know how to do it, and I think the fact that we’re changing the environment on the Earth inadvertently underscores the fact that we really don’t understand how climates work. Despite that, a lot of people have been speculating in the press lately about how easy it might be to terraform Mars. Our paper will be an interesting contrast to that, in terms of dashing some people’s hopes, to be honest.

Interviewer: Ellie Mackay

Well that doesn’t sound very encouraging, but to start off with, can you explain what’s actually being proposed? So, from a scientific point of view, how might we overcome these barriers of temperature and pressure?

Interviewee: Bruce Jakosky

If we wanted to terraform Mars, the way we would do it would be to put a greenhouse gas in the atmosphere. That would serve both functions of increasing the pressure and by trapping heat from the sun, increasing the temperature. And that really depends on the availability of greenhouse gases or our ability to manufacture them. The most available and accessible greenhouse gas at Mars would be carbon dioxide – CO2.

Interviewer: Ellie Mackay

Okay, and so this is what your research was looking at?

Interviewee: Bruce Jakosky

So, we wanted to look at the inventory of CO2 on the planet – where reservoirs of CO2, if you will, reside, how much would be there, and how easy it would be to mobilise it and put it back into the atmosphere.

Interviewer: Ellie Mackay

Essentially, that’s what we’re doing to this planet with global warming and we’re trying to force a way to do that somewhere else. So it’s like we could send all of our industry and all of our fossil fuel burning over to Mars, and it would have a beneficial effect over there, instead of…

Interviewee: Bruce Jakosky

That’s absolutely right. We don’t even need to send the manufacturing and industry to Mars, we could just ship all the CO2 there. And that would solve both planets’ problems. It’s totally facetious and absolutely unworkable. We don’t have that much CO2 in our atmosphere, and the number of rockets you would have to ship to get the CO2 there is immense.

Interviewer: Ellie Mackay

Okay, so if we can’t ship it there, let’s get back to this idea of using reserves of CO2 on Mars. Your paper mentions several possible sinks – there’s CO2 in the polar ice, there’s some in minerals called carbonates, and there’s gas that gets bound to the layer of soil called the regolith on the surface of the planet. So, that seems like a lot of different places for the CO2 to be trapped. How might we mobilise or release it from these sources?

Interviewee: Bruce Jakosky

Probably the easiest is the CO2 locked up in the polar ice. All you need to do is spread dark dust over the polar caps, and it would absorb more sunlight and heat up. That’s the easiest one, and if that sounds hard, you may not like the next ones. The carbonates you have to heat up to temperatures at which they break apart, and that’s around 300 °C. That automatically means a large scale industrial operation, and it wouldn’t get you very much. I think the most difficult CO2 to mobilise is gas that is physically attached to the soil. You would almost have to strip-mine the entire planet in order to put that gas back into the atmosphere, and that won’t work because once you put it there it’ll go right back into the regolith. So this question of how easy it is to get it out of these sinks and into the atmosphere is a really important one. Ultimately, it’s not possible.

Interviewer: Ellie Mackay

If it were to become possible to do somehow, melting the polar ice caps seems to be the most popular solution. How much CO2 is actually trapped there?

Interviewee: Bruce Jakosky

At one time we thought there might have been the equivalent of an Earth’s atmosphere of gas in the polar caps, but that idea is demonstrably wrong based on our knowledge today. The estimates today are that if you put all the CO2 in the polar caps into the atmosphere it would only double the atmospheric pressure.

Interviewer: Ellie Mackay

So that’s not even close?

Interviewee: Bruce Jakosky

No, so that’s a very small increment. This amount of CO2 just isn’t enough to even have a start at raising the temperature or the pressure.

Interviewer: Ellie Mackay

And what about if we added the CO2 from the other sources, the rocks and the minerals, the soil, and released all of the CO2 from all these different reserves?

Interviewee: Bruce Jakosky

We’ve looked at how much CO2 can be locked up in each of these sinks for CO2 that are remaining on the planet. If we could mobilise all of it and put it back into the atmosphere, we would still have less than 10% of the amount of CO2 we need to raise the temperature. So, the most we can get is a tiny fraction of what would be needed.

Interviewer: Ellie Mackay

Is that what you expected to find?

Interviewee: Bruce Jakosky

It’s the answer we knew going in. I think within the Mars community this is not a surprising answer. I’ll be honest, that’s why we wrote this paper, because people are getting up and talking about how easy it is to terraform the planet, without having a realistic understanding of what would be involved and where the CO2 is and how much there is.

Interviewer: Ellie Mackay

So, does this mean this is the end of the concept of terraforming Mars?

Interviewee: Bruce Jakosky

This doesn’t mean we can’t terraform the planet. It means we can’t do it today with available technology. People have also talked about manufacturing molecules that are very effective greenhouse gases, things like Freon, but the scale of manufacturing that would be required to produce enough is so far beyond our current capability that you have to put it into the distant future.

Interviewer: Ellie Mackay

So what would you say to those people who are keen to inhabit Mars in the relatively near future?

Interviewee: Bruce Jakosky

Well first of all, I don’t think this impacts either our desire or our ability to explore Mars with humans. We can carry out that kind of a mission beginning today, and it would be exciting from the human perspective and from the science perspective. And this is part of that process of discussing what’s possible and where we as a society want to head. I think if we’re going to talk about sending humans to Mars, we need to do it in the context of a real and valid understanding of what is on the planet, based on the best available scientific information today.

Interviewer: Ellie Mackay

That was Bruce Jakosky from the University of Colorado in the US. To read that story in Nature Astronomy, you can head over to nature.com/natastron.

Host: Adam Levy

Still to come in the Research Highlights: a dinosaur with enormous feet, and some rapidly rotating nanoparticles. But before that though, we humans love to put things in categories. Look, I’ll show you. Ellie, what is in this picture?

Host: Ellie Mackay

Well, that’s a rainbow over some mountains.

Host: Adam Levy

And can you describe what that rainbow looks like?

Host: Ellie Mackay

Well, it’s a rainbow, so red, orange, yellow, green…

Host: Adam Levy

Yes, exactly! So, you are listing colours. But the rainbow is actually a continuous gradient – a gradual transition from one end of the visual spectrum to the other. We humans categorise, we put each colour in camps. For me, it’s red up to here, and then starts being orange, and then yellow starts about here. We don’t just do this with colour of course, it’s especially important that we do this with language, where we need to know exactly what someone’s saying.

Interviewee: Steve Nowicki

A very well-known example is the distinction between the sounds ‘pa’ and ‘ba’.

Interviewer: Adam Levy

This is biologist Steve Nowicki. These words ‘pa’ and ‘ba’ sound very distinct. But even when a word is actually somewhere in between, a combination of the ‘pa’ and ‘ba’ you just heard, our minds categorise it as one or the other. To me, even knowing that that was a mashup of the two other recordings, it still sounded like ‘ba’. But maybe that’s just because I’ve heard it so many times. Here it is again. I just can’t help categorising it. And you probably did the same. That’s just what we humans do.

Interviewee: Steve Nowicki

And that’s very useful for us to be able to distinguish the parts of speech and to understand people clearly.

Interviewer: Adam Levy

And it’s not just us humans who like to categorise things.

[Zebra finch noises]

Interviewer: Adam Levy

Steve wanted to find out whether a bird – the zebra finch – saw colour in a categorised way, like Ellie saw that picture of the rainbow.

[Zebra finch noises]

I called him up, and we started out by discussing how these small birds interact with colour in their daily lives.

Interviewee: Steve Nowicki

We know that these zebra finches, the females pay attention to the colour of the male’s beak, which can vary from quite orange to like quite dark red. And they prefer to mate with males having the darker red beak, and that’s what led us to ask well, is that continuous variation or is it categorical – it’s either orange or red.

Interviewer: Adam Levy

Of course, you can’t just sit a zebra finch down and say ‘Do you perceive this colour categorically different to this colour?’ How did you end up testing this out in zebra finches?

Interviewee: Steve Nowicki

You can train a bird to look for food under a little disc. Once they’ve learned that, then we trained them that the only discs under which they’ll find a food reward are ones that are bicolour so half of the circle is one colour, the other half of the circle is the other colour. So, then the trick of the experiments was to now start varying how different the two sides of the circle were. And so by varying how close those colours were along this spectrum from orange to red, we were able to determine that there is a breakpoint. On one side they think the colours are mostly just orange, and on the other side of that breakpoint they think the colours are mostly red, and it’s only when you cross that breakpoint that the birds say ‘oh, those are two different colours’.

Interviewer: Adam Levy

So what does that actually mean about the bird’s perception of the world and of colour?

Interviewee: Steve Nowicki

It suggests that even though the colour is varying in a continuous fashion from lighter orange to a darker red, the bird is labelling those colours either as orange on one side of the boundary, or as red on the other side of the boundary. So, in a sense, the birds themselves are like humans labelling colours as opposed to just seeing a continuum.

Interviewer: Adam Levy

Now could this just be because this is how these zebra finches’ eyes work? You know, maybe their eyes just have a breakpoint somewhere between orange and red?

Interviewee: Steve Nowicki

That was a question we asked. But as far as we know, based on what we can know so far, the answer is not that it’s just the way the eyes work. One can put into a model and make a prediction as to whether where we found the boundary from our behavioural data, matches what should be coming out of the way that we know bird photoreceptors would be gathering information about colour, and there the answer was no.

Interviewer: Adam Levy

So we now see that there is this kind of boundary for the finches between orange and red, where on one side they see orange, the other side they see red. Why do they see the world like this? What reason could there be for their perception to have this kind of breakpoint?

Interviewee: Steve Nowicki

It’s possible that this is just the way that animals in general parse out information about colours in the world, in which case that will lead us down one set of conclusions. It’s also possible that this is something that’s special given that these colours – the red/orange spectrum – are important in signalling. That would bring me back to the ‘pa’/’ba’, right? We know that that discrimination is really important in human speech, and it maybe that when it’s about information in a signal, when an animal has to look at something and make a decision, that it’s just more efficient. That selection, natural selection or sexual selection, is acted to sort of say let’s just draw a boundary here because, you know, it’s more efficient to just say orange or red and not to, you know, worry too much about the fine points in between.

Interviewer: Adam Levy

That was Steve Nowicki, who’s based at Duke University in the United States. Read his full study over at nature.com/nature.

Host: Ellie Mackay

Coming up in the News Chat, we’ll have even more news about Mars. And, how an immense black hole at the centre of our galaxy is helping researchers test general relatively. Next though, Benjamin Thompson is here with a quick one-two of science in this week’s Research Highlights.

[Jingle]

Host: Benjamin Thompson

If you find some giant footprints, you may think you’re on the trail of the mythical Bigfoot, but palaeontologists say they found the real Bigfoot, a dinosaur with feet over a metre wide. This creature may have the largest feet ever discovered, although rather than footprints, all that remains are some fossilised foot bones. The bones were excavated in Wyoming, and came from a huge long-necked sauropod dinosaur that would have been stamping around the region, around 150 million years ago. This find tells scientists more about the distribution of large dinosaurs in North America during the Late Jurassic. Stomp over to this research at PeerJ.

[Jingle]

Host: Benjamin Thompson

In more record-breaking news, two groups of researchers have persuaded particles to pirouette at over 1 billion revolutions per second. Both sets of experiments used lasers to levitate and spin silica in a vacuum. One group used individual silica nanoparticles, while the other used ‘nanodumbbells’, made of two silica nanoparticles joined together. These super speedy spins have smashed the previous revolution record by a factor of around 100. It’s thought that the techniques involved could be useful in astrophysics, for example, helping to test the hypothesis that rapidly spinning dust particles in space are responsible for certain frequencies in the cosmic background radiation. Give those papers a whirl over at Physical Review Letters.

[Jingle]

Host: Adam Levy

Ellie, I must say that I’m pretty glad this studio has air conditioning. It’s been oppressively hot lately in London.

Host: Ellie Mackay

Yeah, thanks climate change.

Host: Adam Levy

I don’t think you can say that.

Host: Ellie Mackay

Why not?

Host: Adam Levy

Well, instead of saying that a particular weather event is caused by climate change, don’t you have to say something like ‘This event is consistent with our understanding of climate change, and scientists expect there to be more extreme weather events as the world continues to warm.’

Host: Ellie Mackay

Well, sure, I know that attributing to individual weather events to climate change is normally pretty difficult. Climate change studies are often broad and global. They look at mean changes over large time periods and spatial scales, rather than a particular event. But that is until researchers like Friederike Otto started getting more specific. By turning her models to particular places and timescales, she is trying to calculate how much blame can be attributed to climate change for a given extreme weather event. These kinds of attribution studies are changing the way people think about climate change, replacing the broad general statements with specific direct numbers. Reporter Noah Baker called up Friederike to find out more.

Interviewee: Friederike Otto

What scientists have been able to say before is that in a warming climate, we expect the likelihood of heatwaves to increase, and we can also say how we have predicted that to increase in different parts of the world. But with these studies that we are doing, we are able to quantify the effect of climate change in a specific location at a specific time of year. So at the moment for example, we have a heatwave here in Northern Europe, and we have just done the study where we looked at individual parts of Northern Europe.

Interviewer: Noah Baker

Tell me, how much more likely was this heatwave to occur, as a result of climate change?

Interviewee: Friederike Otto

Five times.

Interviewer: Noah Baker

That seems like a very significant number, and also one that must be difficult to calculate. It’s only recently that people like you and your group have been able to come up with numbers like this. What is it that’s changed to allow you to do that?

Interviewee: Friederike Otto

In order to look at extreme events, we need to be able to run a climate model many hundreds of time, and that only has been possible with computer power in the last maybe ten years. And then we also needed to develop methodologies and find out the best way of doing these attribution studies toactually also have confidence and assess the robustness of our results, and so that of course also plays a role and takes a bit of time.

Interviewer: Noah Baker

Now, just to clarify here, you’re not at the stage where you can say something like ‘This heatwave was caused by climate change’, that statement you can’t quite make yet.

Interviewee: Friederike Otto

Well, yes we can make that statement, but it depends on what you mean by the word ‘cause’. So, in the same way that you can say smoking causes cancer, we can say this heatwave was caused by climate change. But it’s always a probabilistic causality because every extreme event always has multiple causes.

Interviewer: Noah Baker

Do you have sort of an end goal with this? Is this just pure scientific curiosity, or are you hoping that the results of these attribution studies might make a difference either scientifically, or even just policy or to help people think about climate change?

Interviewee: Friederike Otto

I think from a societal point of view, there are two reasons why we do this. The first reason is people asked the question. So when extreme events are happening, people ask the question what’s the role of climate change? And until very recently, before we were able to answer these questions, scientists would not say anything or they would say it’s the kind of event we expect in a changing climate, but they couldn't really give any numbers or pin it down to this individual event. But politicians will give an answer, or people with a different agenda. The second reason is when an extreme event happens, you usually have a window of opportunity to do something about the vulnerability to this kind of event.

Interviewer: Noah Baker

A big part of doing something like that is speed and timeliness, you know, there’s no point in coming up with a study on an event that happened 10 years ago for something that might need a quick policy decision.

Interviewee: Friederike Otto

Yes. So, the aim of that initiative is to provide attribution results when people are asking the question. So, I think this week was actually our record. So we started on Tuesday, and we have the press briefing just today on Friday…

Interviewer: Noah Baker

Tuesday, Wednesday, Thursday Friday – so that’s sort of a 3-4 day turnaround to a press briefing. But would it be possible to in the future, to not even need a press briefing? You could just post as soon as a heatwave is happening on social media and say this heatwave happened because of climate change or this heatwave was 5 or 6 times more likely because of the, you know, the impacts of climate change.

Interviewee: Friederike Otto

What I hope for in the future is that we don’t have to do this for the events where the methods are really advanced and where we have developed a good strategy on how to do this, and also on how to do this quickly. But the operational centres in this world would do this, and that we in our research could focus on the more complicated events. Because at the moment we are quite confident with heatwaves, with extreme precipitation, we have done quite a few droughts, but we only have done two maybe studies on windstorms, but they are of course also very, very important. There are other types of events that we can’t robustly attribute yet, where it would be great to be able to focus on the research.

Interviewer: Noah Baker

Do you think things like attribution studies will make scientists’ voice louder in this argument? Do you think they will be able to be heard more?

Interviewee: Friederike Otto

I think so, yes. Being able give concrete evidence, concrete number for a specific event where we can say yes, we have looked at this particular part in the world and we can say that climate change made this heatwave in your backyard 10 times more likely. That is more heard than if you would only be able to say that it’s the kind of thing we expect from our physical understanding.

Host: Ellie Mackay

That was Friederike Otto from the University of Oxford in the UK, speaking with Noah Baker. Friederike’s work has already come up with some eye catching results. As well as the European heatwave, her team also studied the recent drought in Cape Town, South Africa, and concluded that climate change had made this event 3 times more likely. And looking forward, according to her models, if the world warms by another degree, it will be 3 times more likely again. Find out more about attribution studies over at nature.com/news, where there’s a great Feature which should help you out.

Interviewer: Adam Levy

Finally this week, it’s time for the News Chat and space reporter with Nature, Alex Witze, joins us on the line from Colorado. Hello Alex.

Interviewee: Alex Witze

Hello Adam.

Interviewer: Adam Levy

Well Alex, earlier in the show we had a story pouring cold water on the idea of terraforming Mars. But anyone who’s been paying any attention to the science news this past week will know this isn’t the first time the words cold, water, and Mars have been mentioned in the same sentence. Alex, what is the big news from the red planet?

Interviewee: Alex Witze

Well this week we had a really exciting potential discovery. It’s one of those things that if it pans out to be true, it’s super exciting. What’s happening is a team of European scientists say they have found a lake on Mars, so liquid water on Mars. Now, it’s not on the surface, it’s icy and cold. This potential lake is very beneath the ice, near the martian south pole.

Interviewer: Adam Levy

And how was it actually spotted if it’s under the surface?

Interviewee: Alex Witze

It was spotted sort of indirectly from the Mars Express spacecraft – that’s the European Space Agency’s probe that’s been orbiting since 2003. So this probe’s been at Mars for quite a long time, and it’s got an instrument on it that uses radar to sort of bounce radio waves down to the surface and back. And sort of like using ground-penetrating radar on Earth to find things like oil and gas deposits that are buried, this Mars Express radar uses its own instruments to probe the subsurface, to look at what’s bouncing back from beneath the ice. And it spotted these very, very bright reflections in this one place beneath the ice cap, and they’re interpreting those bright reflections as being liquid water.

Interviewer: Adam Levy

How big a deal actually is this? How much does this change our picture of water on the red planet?

Interviewee: Alex Witze

It’s both a big deal and not a big deal, depending on how you think about it. The less exciting way to think about it is that we have known there’s water on Mars in various capacities. We know there’s ice frozen at the poles, we’ve seen ice sort of frozen into the soil at different points around the planet, but it’s always been solid, it’s always been frozen. So the really big thing would be this is the first time we’ve seen it today liquid. And that’s a big deal because of course, water is considered a habitat, or at least something you need for life. So if we’ve got little Martians, if we’ve got Martian microbes, this is a place where they could live. Maybe, just maybe.

Interviewer: Adam Levy

So what does that maybe actually mean? How certain are these findings of this liquid water on Mars?

Interviewee: Alex Witze

So, people have been trying to use radar to look for liquid water on Mars for a very long time, for more than decade. And it’s just really tricky to interpret these reflections. We talked about these radio waves bouncing back and they looked like a really bright reflection, and so the sort of question here is whether the analysis of the radar data will hold up. Something is there, the question is, is it water?

Interviewer: Adam Levy

If we’re able to settle that question and at some point say yes, that definitely is liquid water, does that then mean there is also life there?

Interviewee: Alex Witze

We don’t know – could be… maybe not. The next step that scientists talk about wanting to take is to see whether this one body of water, this one lake beneath the ice cap, whether there are more. And the idea is that this might be kind of a refuge perhaps for microbes that have been around for a very long time. The idea being that Mars, early in its history, billions of years ago, was warmer and wetter than today, almost a blue planet like Earth and life perhaps could have thrived there like it thrived on ancient Earth. And then as Mars sort of dried up and got colder and lost most of its atmosphere, where did those microbes go? Well, maybe they retreated sort of under the polar caps where they found little bits of water to hang on with.

Interviewer: Adam Levy

How would we actually be able to find out? This water, if it’s there, it’s more than a kilometre under the surface.

Interviewee: Alex Witze

I talked to one of the scientists who leads drilling projects in Antarctica, and he was talking about the huge amount of equipment they haul out onto the ice, and then they have a hot water drill, and then they melt a core down and get to the water beneath. But how do you fly all that stuff to Mars, right? I think there’s got to be a lot of technological advances, I think it’s safe to say, before we could probably go sample it. It’s just too tough to get there for the foreseeable future.

Interviewer: Adam Levy

For our second story this week, let’s go even further afield, and astronomers have been studying the behaviour of the black hole at the centre of our galaxy. What were they actually watching?

Interviewee: Alex Witze

This is an amazing project that’s been going on. There are two competing teams that have been looking at the centre of our galaxy for more than two decades. They use some of the world’s largest telescopes to watch how stars essentially dance around the centre of our Milky Way. There’s a supermassive black hole there, something like 4 million times the mass of our Sun, and that’s a heck of a lot of gravity – this big, intense black hole sucking in everything. And stars that are just a little bit too unfortunate and they get a little bit too close to the black hole, you can see them kind of skirt as they move by over time. And these two teams have been watching this one particular star every 16 years loop around this black hole, and as it sort of whizzes by its close approach, it has kind of a super scary passage, it just kind of squeaks right by and moves along, and manages to escape its gravity. But it’s sort of a two decade-long watching this star kind of eke it’s way past the black hole.

Interviewer: Adam Levy

Could you give some sense of how extreme this is? How fast is this star orbiting around the black hole?

Interviewee: Alex Witze

It’s crazy, it’s crazy fast. So, as it’s making its closest approach, it’s going more than 7,600 kilometres every second, so that’s almost 3% the speed of light, and it’s some of the fastest stuff we’ve ever measured at these relativistic speeds.

Interviewer: Adam Levy

And how was this observation actually made?

Interviewee: Alex Witze

They look at the path of the star. So, they literally watch the star, you know, week after week, they take pictures as the star moves past, and they also measure it’s light in the direction as it’s moving to and way from Earth – something called radio velocity. And by combining this, they detected something that they have been looking for since the time of Einstein – a stretching of the star’s light. It’s basically the gravity of the black hole at the centre of the Milky Way is stretching this star’s light towards the red. It’s a very, very small, very precise, very esoteric prediction that Einstein made all those years ago through general relativity, and the teams spotted it for the very first time.

Interviewer: Adam Levy

And their observations, they’re consistent with general relativity?

Interviewee: Alex Witze

Absolutely. So guess what, Einstein was right. Einstein’s always right! Don’t bet against Einstein.

Interviewer: Adam Levy

Besides confirming Einstein once again, is there anything new to learn from watching this star? Something that we can learn about how black holes behave?

Interviewee: Alex Witze

If they keep watching this star over the next months to years, they hope to detect other phenomena they’ve never seen before, like for instance, how the centre of the Milky Way drags space and time around with it as it rotates.

Interviewer: Adam Levy

Well, hopefully we’ll have an update as more observations come in, but in the meantime, Alex thank you for joining us. More on both those news stories over at nature.com/news.

Host: Ellie Mackay

That’s it for this week’s show. Don’t forget you can get in touch on Twitter @NaturePodcast, or on email: podcast@nature.com. It’s also my last show, so a big thank you to you the listeners, and thank you to Ben and Adam for being such great co-hosts. I’ve really enjoyed my time here and I’ll be definitely listening excitedly in the future.

Host: Adam Levy

Well, we’re going to miss having you in the studio Ellie, but to help with our withdrawal, where can we find you on social media?

Host: Ellie Mackay

I’m on Twitter and Instagram @EllieWorldwide.

Host: Adam Levy

I look forward to all your tweets and your ‘grams… #downwiththekids. I’m Adam Levy.

Host: Ellie Mackay

And I’m Ellie Mackay. Thanks for listening.

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