Stellar Q&A: Unraveling Fusion Mysteries, Martian Caves & Solar Cycles

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Andrew Dunkley: Hi there. Thanks for joining us. This is a Q

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and A edition of Space Nuts. My name is

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Andrew Dunkley. Thanks for your company. Uh,

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coming up, we're going to answer audience

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questions. Um, one from Ken. Uh,

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I'm going to paraphrase his 500,000 word

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question by saying, why don't the numbers add

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up when turning hydrogen into helium?

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Also, a question from Mark about caves on

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Mars and Casey wants

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to talk about changes in stars.

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That's all coming up on this Q and A edition

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of space nuts. 15 seconds. Guidance is

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internal. 10, 9,

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ignition sequence start. Space nuts.

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Jonti Horner: 5, 4, 3, 2.

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Andrew Dunkley: 1. 2, 3, 4, 5, 5, 4, 3,

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2, 1.

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Jonti Horner: Space nuts.

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Andrew Dunkley: Astronauts report it feels good.

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I just got a text to say my car's been

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serviced, so I'll be back in about 20 minutes

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if you just want to. Hang on. I'm kidding.

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Uh, joining us to answer all those questions

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is Professor Jonty Horner, professor of

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Astrophysics at the University of Southern

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Queensland. Hi, Jonty. Good day.

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Jonti Horner: How are you going to.

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Andrew Dunkley: I am m. All right. Good to see you again.

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Jonti Horner: It's good to be back. I was going to say the

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amount I've been talking too much. You've

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probably got time to go and get the car and I

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could probably

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Andrew Dunkley: ask you a question, bolt down and get the car

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and come back just in time to hear the end

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of the first sentence.

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Jonti Horner: Yes, and I do apologise to listeners if I've

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rambled on too much, but it's when you get to

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talk about your hobby and people have to

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listen, it's, you know, hard not to get

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excited and it is, isn't it?

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Andrew Dunkley: It is.

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Let's get, uh, straight into our first

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question. Hi, Andrew and Jonty. I'm going to

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say it's not what he wrote, but anyway, it

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doesn't matter. Ken, uh, from Maroochydore,

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longtime listener and fan and love the way

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you make complex issues sound simple. I am

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trying to understand the basic fusion

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reaction that both me and my accountant are

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struggling with. Uh, the basic fusion

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reaction in our sun converts hydrogen to

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helium. To summarise the reaction, four

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hydrogen nuclei, I.e. four protons,

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go through two steps to create one

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helium nucleus containing two neutrons

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and two protons. Additionally, gamma rays,

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neutrinos and positrons are released.

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My anatomy textbook tells me that about

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600 million tonnes of hydrogen convert to

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596 million tonnes of helium every

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second. The 4 million tonnes is

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conveyed to energy as per E equals

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MC squared. If neutrons had a lower

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mass than protons it would all make perfect,

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perfect sense, but they don't. They have a

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higher mass. So the mass of the helium

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nucleus is higher than the mass of the four

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protons. All the explanations I've read

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sound pretty dodgy, and my accountant says he

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could never get away with such, such

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explanations with the tax department.

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Could you please explain the devil in the

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detail that I'm missing? I, uh, love it.

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That's a great question. And thanks for the

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research, Ken. Hope all is well in

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Maroochydore. Not far from you, just a bit

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further up the coast.

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Jonti Horner: Yes, out to the coast and up a bit north of

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Brisbane, up on the sunshine course, which is

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kind of lovely area.

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Andrew Dunkley: It's kind of, it's only kind of lovely.

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Jonti Horner: Yeah, only kind of lovely. It's getting,

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getting very aggressively more and more

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touristed. Tracks a slightly different

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tourist demographic to the Gold coast, which

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is south of Brisbane, um, but is still

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a little bit more touristy than you'd like

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it. It's a little bit like hippie central,

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but not to the level of Byron nuts.

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Andrew Dunkley: Yeah, I get you. Yeah, yeah, yeah.

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Byron is the hippie, uh, capital of the, of

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the country, I think. Or to, to

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be more like Nimbin a bit further down.

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That's, that's very, very hippie.

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Anyway, um, so,

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yeah, he doesn't understand the balance. It

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doesn't. It doesn't. To paraphrase, why don't

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the numbers add up when turning hydrogen into

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helium? That's the short version of the

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question.

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Jonti Horner: And I totally get that. Because if you look

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at the masses of protons and

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neutrons in isolation and add them together,

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helium is two protons, two neutrons. Add them

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together, taking the mass of a proton and the

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mass of a neutron, and you get a given value

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for the mass of a helium nucleus. And

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then you look at the mass of a helium nucleus

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and it isn't that mass. And that doesn't make

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sense because if you've got four nucleons

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together, surely the mass of the nucleus is

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the four nucleons added together. And that's

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effectively the fundamental of what's being

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said here. Added to which a, uh,

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hydrogen nucleus is a proton, a deuterium

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nucleus is a proton and a neutron, but

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hydrogen nucleus is a proton. Four hydrogen

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nuclei go together to make a helium nucleus,

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which is 2 protons, 2 neutrons and M. In the

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process, you kick a few things out and do a

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few weird things, surely. Therefore,

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four hydrogen nuclei have the mass of

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four protons. One helium nucleus has a mass

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of two Protons plus two neutrons. And when

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you get the numbers off Wikipedia, that would

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suggest that the helium nucleus should be

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more massive than hydrogen and you should

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lose energy rather than create it, because

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you've had to create mass. Fundamentally in

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actuality though, the mass of the helium

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nucleus is lower than the mass of two

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protons plus two neutrons. And that's

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where the misunderstandings coming in, or not

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really misunderstanding, that's where the

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complexity and the confusion comes in

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and takes everybody a little bit to get your

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head around this when you first come across

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it. Helium nucleus, quite rightly is

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made of two protons and two neutrons. But

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those two protons and neutrons are held

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together. They're bound together by the

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nuclear force, held in strongly enough that

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the repulsion from the two positively charged

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things don't blow it apart. So there is

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something going on called the binding energy.

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And the binding energy is the amount of

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energy you would have to throw at a helium

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nucleus to separate the two protons and

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the two neutrons and make them fly through

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space separately. Again with the energy and

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mass equivalence. If you were to do that,

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you would then have 4, 4 nucleons

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independently of each other, which would have

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the mass we've just calculated. But you've

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had to add energy and energy is equivalent to

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mass. So what it's saying is that the mass of

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a helium nucleus is lower than the

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mass you would expect from the four nucleons

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because of the effect of this binding energy

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that's in there. And that binding energy is

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something we can calculate. It's helium is

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remarkably high compared to the things on

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either side of it. Helium 3 hydrogen, 3

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lithium, and that is incredibly tightly

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bound. That binding energy

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is what leads to the little bit of mass

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deficit with the helium atom being lighter

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than the four nucleons that went to make it.

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And it's that energy that's released. Now

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this is why nuclear fusion can work, because

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if you put four nucleons

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together from hydrogen atoms and make ah,

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from hydrogen nuclei to make a helium nuclei

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with the binding energy, it means you get

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more energy out than you get in. You produce

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energy. And that's true if you fuse

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helium. Helium is difficult. You can't fuse

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it to anything until carbon because

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lithium, beryllium, boron have a

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lower binding energy per nucleon than helium

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does. So you actually have to put energy in

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to fuse helium to those things rather than

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getting energy out. So that doesn't happen.

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Helium can fuse to carbon, but you need

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three helium nuclei to collide at once.

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Which is hard. From then on, from carbon

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upwards, you can get a little bit of energy

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from fusing heavier and heavier things

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together until you get to iron. Iron 56

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has the highest amount of binding energy per

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nucleon. So if you try and fuse

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hydrogen, fuse iron atoms to make a heavier

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atom than iron, you have to put more energy

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in than you get out. And that's what causes

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stars fundamentally to go supernova, is that

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they fuse heavier and heavier things to iron

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and then the fuel sources cut off suddenly,

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they then collapse. You get a boom because of

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the shockwave going bouncy, bouncy. Some of

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the energy from that supernova,

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uh, gets taken up in the fusion of iron to

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make heavier elements and gets sunk into

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that, which is where we get all the elements

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heavier than iron, everything up to uranium

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and beyond those things heavier than

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iron, the binding energy per nucleon gets

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lower and lower the further up you go. Which

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is why for things heavier than iron,

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nuclear fusion costs energy, but nuclear

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fission liberates energy because you're going

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back up the slope again. So uranium

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fissioning to be become lighter elements

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gives off energy because of that binding

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energy difference. It's all part of the same

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thing. Now I, I understand that

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intuitively this really isn't a

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satisfying answer because this binding energy

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sounds a bit like your accountant thinking

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you've got a tax dodge. It's a bit like

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capital gains tax or fringe benefits or, or

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uh, what is it? Negative gearing? Binding

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energy may well be the negative gearing of

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the cosmos because it's when you put four

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nucleons together, they're wear less than

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they would do on their own.

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Um, it's ultimate waste loss plan. But it is

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this bind that leads to the mass you

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would measure for a helium nucleus being less

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than the mass you would measure for hydrogen

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nuclei. And it's a mass as you measure, not

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the masses of the individual components. If

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you took them out and put them on their own,

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that is the important thing. This is usually

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skipped in the explanations. And this is

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where the challenges come in. Because in the

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explanations you just say a helium atom is

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less massive than four hydrogen atoms.

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Ergo some mass has been lost. Therefore

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energy is produced by equals MC squared. And

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it skips all this discussion of the particle

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physics underpinning it on um, this binding

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energy. As always, there is a fairly

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detailed discussion of this in the wikipedia

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page for Helium 4. Talking about the

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stability and that's got the binding energy

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curve in. There is also discussions of

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binding energy and that out there. And

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particle Physics out there. It is basically

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though, that the binding energy causes this

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mass deficit. And it's that mass deficit that

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has been converted to energy that it's

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in liberated in fusion. So I

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appreciate it is not the most satisfying

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answer, but that's our

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understanding of the why behind all of this.

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And the proof is in the pudding. Fusion

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happens. It produces energy at the

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right level that we calculate that all, all

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of our models suggest it should do. So it

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seems that this is a very accurate

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representation of how the world works, even

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if it doesn't immediately feel

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satisfying and commonsensical. And uh,

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part of that is that common sense we've

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developed based on the experience of the

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world around us at our scales, at macroscopic

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scales. And the further you go from the

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conditions in this room, the less accurate

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modern sense, common sense is at predicting

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the outcomes of things. And that's why

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it's hard to work these things out.

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Andrew Dunkley: Yeah, it's like, I mean, listening

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to your explanation would be the same as me

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trying to explain to a kangaroo how to use

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a pedestrian crossing. So, you know,

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it's. I can understand Ken's

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frustration. Um, but

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if I understand your explanation thoroughly,

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um, Ken, what, what Jonty was saying

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was that shift happens.

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That's basically it, I think. But thanks for

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the question. Great to hear from you. This is

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a Q and A edition of Space Nuts with Andrew

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Dunkley and Professor Johnty Horner.

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Jonti Horner: Space Nuts.

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Andrew Dunkley: Okay, Jonty, our next question says,

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uh, Fred Watson was talking about caves on

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Mars and that got me thinking. The caves on

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Earth are, uh, primarily made of limestone,

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which has high concentrations of CO2

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that was locked in by millions of years of

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sea creatures popping into the sea, creating

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a layer on the seabed that could be,

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uh, um, seabed. Could it be the same effect

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on Mars? No. Punctuation caught me out

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there. If so, I need to ask, ah,

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the question. Um, you get,

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uh. If

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so, I don't need to ask the next question.

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Um, you get what I mean. But the next

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question is, if caves are deep enough,

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could it be possible that the atmosphere at

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the base of these caves could be dense enough

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to create a stable atmosphere with higher

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concentrations of oxygen for life? And could

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that life be looking at Earth with

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envious eyes?

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Jonti Horner: Yeah, very funny.

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Andrew Dunkley: Hope not. Uh, Mark? Uh, thank you, Mark.

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So, um, caves on Earth, we. Yeah, not all of

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them, but uh, quite a lot of them are

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limestone. Um, could it be the

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same way as caves were created

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on Mars? I think that's the initial question.

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Jonti Horner: So I'd stress here, I'm Not a geophysicist,

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but the limestone we get on Earth is stuff

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that is now above sea level that was once

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below sea level. You had all these calcium

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shelled creatures die and fall to the bottom

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of the, uh, ocean and then get compacted over

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millions of years to form this rock. And then

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plate tectonics lifted the rock above the

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surface of the ocean. I guess on Mars you'd

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probably argue the oceans went away. There's

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not plate tectonics to lift things up, but

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the places that were ocean now no longer

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are. Ah, this is

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predisposed on the idea that you develop

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things with enough calcium

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to be able to make shells and stuff like

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that. Um, I believe, and I stand to

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be corrected on this, that the things that

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make calcium are typically

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oxygen breathers, not carbon dioxide

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breathers. But I may be wrong on that. Um,

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they die, they precipitate stuff out. Now,

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the first point is whether they could be

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limestone caves on Mars. Ah, now that would

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be predisposed on the appropriate

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evolution of life to get to the point where

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you have things that could leave fossils,

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that could leave shells and stuff. And we

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haven't yet found any fossils of such life on

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Mars. And without such life, you couldn't get

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limestone. I think think will be an open

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question. I suspect if we got Earth, uh,

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scientists and stuff like that in on the

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show, they'd have good reasons why limestone

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will be unlikely to be common on Mars.

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Because, yes, you did have oceans and lakes,

351
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but was there, ah, enough time for

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enough deposits to be made of shelled

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creatures which we don't even know evolved?

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So there's a lot of complexity there. It's

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obviously something, I don't know for

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definite whether you could have limestone

357
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on Mars. Um, I haven't heard of it being

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detected on Mars, but absence of evidence

359
00:14:25.080 --> 00:14:26.680
is not evidence of absence. But I don't

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believe it is common, otherwise we'd be

361
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fairly well aware of it. But there are other

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ways you can get caves on Earth. And I mean,

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we've got lava tubes and lava caves up

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in North Queensland in Uladulla. We've got

365
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similar things have been found on the Moon

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and Mars. There are skylights and lava tubes

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on Mars that people have even suggested could

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be suitable places for humans to

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go and live. Because if you're underground,

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you're shielded from radiation. And of

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course, if you're in a cave, you can seal the

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entrance and fill it with air, which would be

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good. Now that kind of links to the second

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part of the question here from Mark, which is

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if you have caves deep enough, could you have

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enough atmosphere in those caves to have

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atmospheric pressure? I think that's

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unlikely here because those cave

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systems would probably be connected to the

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surface and air would diffuse out of

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them. So you equilibriate and you don't

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go into the cave in the lava tube on Earth,

383
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and suddenly it's 3 atmospheres. Because if

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it was 3 atmospheres, the air would be pushed

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out the entrance. So I don't

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think you get to atmospheric pressure in

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these caves unless they were very, very deep

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and were sealed and the air was sealed in

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from when the atmospheric pressure was higher

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and it hadn't escaped. But with the porosity

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of the rocks, I think that would be very

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unlikely. The next thing is about there being

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oxygen in those caves. And I think of all of

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these things, that is the least likely

395
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because Mars

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doesn't have much, if any free oxygen

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in the atmosphere, because oxygen reacts with

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everything. And on Mars, there are bits of

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00:15:59.350 --> 00:16:00.990
methane being produced. We're not quite sure

400
00:16:00.990 --> 00:16:03.270
what's going on there, but the oxygen, free

401
00:16:03.270 --> 00:16:06.030
oxygen from Mars has been very

402
00:16:06.030 --> 00:16:08.950
effectively absorbed into the surface through

403
00:16:08.950 --> 00:16:11.510
chemistry. Um, big part of why Mars looks

404
00:16:11.510 --> 00:16:12.950
red, of course, is that you can effectively

405
00:16:12.950 --> 00:16:15.310
say the surface is rusted iron

406
00:16:15.310 --> 00:16:18.270
oxide. The oxygen in the air has reacted with

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the iron in the surface and

408
00:16:19.990 --> 00:16:22.750
Andrew Dunkley: been locked up like a lot of Australia.

409
00:16:22.910 --> 00:16:25.910
Jonti Horner: Yes. Um, now you can produce some oxygen in

410
00:16:25.910 --> 00:16:28.670
Mars's atmosphere. If you get water into the

411
00:16:28.670 --> 00:16:30.590
atmosphere, and there is a very small amount,

412
00:16:30.590 --> 00:16:32.950
traces of ox of water in Mars's atmosphere,

413
00:16:32.950 --> 00:16:35.430
we do get water clouds there. Without an

414
00:16:35.430 --> 00:16:37.710
ozone layer, some of that water, particularly

415
00:16:37.710 --> 00:16:38.950
the water that gets highest in the

416
00:16:38.950 --> 00:16:41.830
atmosphere, will get dissociated. It will get

417
00:16:41.830 --> 00:16:43.750
broken into hydrogen and oxygen by

418
00:16:43.750 --> 00:16:46.310
ultraviolet radiation and the hydrogen will

419
00:16:46.310 --> 00:16:48.550
then escape because hydrogen atoms travel so

420
00:16:48.550 --> 00:16:50.670
quickly that Mars gravity can't hold them,

421
00:16:50.990 --> 00:16:52.750
which means the hydrogen goes away and the

422
00:16:52.890 --> 00:16:55.090
oxygen is left behind. So you will be

423
00:16:55.090 --> 00:16:57.090
producing small trace amounts of oxygen in

424
00:16:57.090 --> 00:16:59.530
Mars's atmosphere all the time. But then the

425
00:16:59.690 --> 00:17:02.050
oxygen would then be used up in chemistry and

426
00:17:02.050 --> 00:17:04.890
removed. So in order to have large amounts of

427
00:17:04.890 --> 00:17:06.730
oxygen in one of these caves, you'd need a

428
00:17:06.730 --> 00:17:09.330
source of oxygen, and you'd need that source

429
00:17:09.330 --> 00:17:11.570
to provide enough oxygen that the oxygen can

430
00:17:11.570 --> 00:17:13.370
overcome everything that's trying to remove

431
00:17:13.370 --> 00:17:16.210
it. Now, on Earth, it took a

432
00:17:16.210 --> 00:17:18.090
huge fraction of Earth's life before you got

433
00:17:18.090 --> 00:17:20.290
the great oxidation event for life to

434
00:17:20.290 --> 00:17:21.570
actually get to the point where it could

435
00:17:21.570 --> 00:17:23.640
produce more oxygen than the Earth, uh,

436
00:17:23.690 --> 00:17:26.590
system could absorb. So to have abundant

437
00:17:26.590 --> 00:17:28.550
oxygen on Mars, uh, strikes me as Very

438
00:17:28.550 --> 00:17:31.230
unlikely. Maybe possible that in the future

439
00:17:31.230 --> 00:17:32.790
that will change though, because if we went

440
00:17:32.790 --> 00:17:35.550
to Mars, then one of the ways people are

441
00:17:35.550 --> 00:17:37.230
thinking the first human habitats will be

442
00:17:37.230 --> 00:17:39.230
built will be to go to the caves in the lava

443
00:17:39.230 --> 00:17:42.230
tunnels and live there. And then you can make

444
00:17:42.230 --> 00:17:44.230
a sealed environment that you can then pump

445
00:17:44.230 --> 00:17:46.910
with an artificial atmosphere. So it could be

446
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that if you ask that question in 20 years

447
00:17:49.310 --> 00:17:52.030
time, Mark, the answer would be yes. There

448
00:17:52.030 --> 00:17:53.950
are caves with high enough atmospheric

449
00:17:53.950 --> 00:17:56.460
concentrations for life. We've put them

450
00:17:56.460 --> 00:17:58.420
there. Would they be looking back at Earth

451
00:17:58.420 --> 00:18:00.860
with anxious eyes, with envious eyes? I guess

452
00:18:00.860 --> 00:18:02.660
it depends on the person who's emigrated

453
00:18:02.660 --> 00:18:05.220
there. There's these fabulous ideas of what

454
00:18:05.220 --> 00:18:07.060
humanity will look like when we're a multi

455
00:18:07.060 --> 00:18:09.900
planet species. But the thing that stuck with

456
00:18:09.900 --> 00:18:11.579
me more than anything else was this amazing

457
00:18:11.579 --> 00:18:14.189
Talk from a doctor in 2012, 2013,

458
00:18:14.304 --> 00:18:16.620
2014 at one of our space research conferences

459
00:18:17.100 --> 00:18:19.300
who basically talked about the difficulty

460
00:18:19.300 --> 00:18:22.180
humans have reproducing when you go even

461
00:18:22.180 --> 00:18:24.300
very slightly away from standard temperature

462
00:18:24.300 --> 00:18:26.340
pressure at sea level. Talked about the

463
00:18:26.340 --> 00:18:29.000
challenges at invaders had into South

464
00:18:29.000 --> 00:18:30.600
America when they reached the high Andes.

465
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They couldn't colonise there because they

466
00:18:32.320 --> 00:18:35.000
weren't able to reproduce. Talking about very

467
00:18:35.000 --> 00:18:37.240
slight changes in conditions being enough to

468
00:18:37.240 --> 00:18:39.880
render our ability to have children

469
00:18:40.120 --> 00:18:42.760
null and void. On Mars you've got one third

470
00:18:42.760 --> 00:18:45.720
gravity. Unless you get dystopian science

471
00:18:45.720 --> 00:18:48.400
fiction future where women enter

472
00:18:48.400 --> 00:18:50.560
centrifuges for nine months in order to carry

473
00:18:50.560 --> 00:18:52.360
a child to term, in order to simulate one

474
00:18:52.360 --> 00:18:55.350
ghost. The perspective is at least in the

475
00:18:55.350 --> 00:18:58.310
relatively near future, humanity on the

476
00:18:58.310 --> 00:19:00.270
moon, humanity on Mars will be

477
00:19:01.070 --> 00:19:03.430
not self sustaining. We won't be able to have

478
00:19:03.430 --> 00:19:05.950
children there. And so it may well be that

479
00:19:05.950 --> 00:19:08.950
Mars becomes a interplanetary retirement

480
00:19:08.950 --> 00:19:11.270
home. People sow their wild oats, live their

481
00:19:11.270 --> 00:19:13.110
lives and then go to Mars later in life for

482
00:19:13.110 --> 00:19:15.750
the adventure. And then would they look back

483
00:19:15.750 --> 00:19:17.190
with envy? Well, they'd probably look back

484
00:19:17.190 --> 00:19:18.830
with a little bit of longing, but also they'd

485
00:19:18.830 --> 00:19:20.510
have the excitement of where they are are.

486
00:19:20.830 --> 00:19:22.990
So it could be that in 20 years time, 30

487
00:19:22.990 --> 00:19:25.950
years time, there will be life in the caves

488
00:19:26.350 --> 00:19:28.990
with artificially enhanced oxygen levels.

489
00:19:29.070 --> 00:19:31.230
Looking back at Earth, watching the news and

490
00:19:31.230 --> 00:19:33.230
all the rest of it, but I don't think at the

491
00:19:33.230 --> 00:19:34.270
minute that that's the case.

492
00:19:35.070 --> 00:19:38.030
Andrew Dunkley: Okay, fair enough. Uh, and uh, just one

493
00:19:38.030 --> 00:19:40.110
more point, Mark. I just did a quick search

494
00:19:40.110 --> 00:19:42.550
about could there be limestone on Mars? And

495
00:19:42.550 --> 00:19:44.390
according to an article in Science

496
00:19:44.390 --> 00:19:46.590
AstroDailyPod which dates back nearly 20

497
00:19:46.590 --> 00:19:49.350
years now, uh, yes, limestone, specifically

498
00:19:49.350 --> 00:19:51.950
carbonate minerals likely exist on Mars, but

499
00:19:53.220 --> 00:19:55.780
probably not in massive thick sedimentary

500
00:19:55.780 --> 00:19:58.300
beds found On Earth, while early Mars was

501
00:19:58.300 --> 00:20:00.380
warmer and wetter, supporting the potential

502
00:20:00.380 --> 00:20:03.140
for carbonate formation, the planet lacked

503
00:20:03.140 --> 00:20:05.100
the extensive oceans and tectonic plate

504
00:20:05.100 --> 00:20:07.860
activity required to build large limestone

505
00:20:07.860 --> 00:20:10.660
deposits. So there you are. They

506
00:20:10.660 --> 00:20:13.420
think there possibly is limestone

507
00:20:13.420 --> 00:20:16.020
on Mars, but not uh, enough to do

508
00:20:16.100 --> 00:20:18.900
what we've seen on Earth. Uh,

509
00:20:18.900 --> 00:20:21.620
but great question and uh, certainly food for

510
00:20:21.620 --> 00:20:24.400
thought, uh, and appreciate it. Mark, thanks

511
00:20:24.400 --> 00:20:25.120
for sending it in.

512
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This is Space Nuts. Andrew Dunkley here with

513
00:20:27.440 --> 00:20:28.800
Professor Jonty Horner.

514
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Jonti Horner: M. Space Nuts.

515
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Andrew Dunkley: And you're listening to a Q and A edition.

516
00:20:37.360 --> 00:20:39.920
We've got one more question to tackle. Hello,

517
00:20:39.920 --> 00:20:42.560
this is Casey from Colorado, she's one of our

518
00:20:42.560 --> 00:20:45.000
regular contributors. I have some questions

519
00:20:45.000 --> 00:20:47.840
about stars. Why do the activity levels of

520
00:20:47.840 --> 00:20:50.640
stars change? What causes solar cycles?

521
00:20:50.640 --> 00:20:53.420
Does every type of star go through solar

522
00:20:53.420 --> 00:20:56.100
cycling? Love the show, Hope you're both

523
00:20:56.100 --> 00:20:58.780
well. Uh, thanks Casey from Colorado.

524
00:20:59.080 --> 00:21:01.500
Um, it's a good question because we don't

525
00:21:01.500 --> 00:21:03.340
really talk about this sort of thing much,

526
00:21:03.420 --> 00:21:06.060
but uh, we're just about to go out of

527
00:21:06.340 --> 00:21:09.140
uh, the peak of solar activity

528
00:21:09.140 --> 00:21:12.100
in our own Solar System, the 11 year cycle

529
00:21:12.100 --> 00:21:15.060
that they talk about. Uh, so that's probably

530
00:21:15.060 --> 00:21:17.940
where we should start. We know the sun goes

531
00:21:17.940 --> 00:21:20.920
through an 11 year cycle and um,

532
00:21:22.080 --> 00:21:24.520
and we witness different things during those

533
00:21:24.520 --> 00:21:27.200
11 years because it's constantly changing.

534
00:21:27.360 --> 00:21:29.900
Jonti Horner: Yeah, it's worth stressing Shreya, that

535
00:21:29.900 --> 00:21:32.600
uh, effectively all stars are uh,

536
00:21:32.600 --> 00:21:35.560
inherently variable to some degree. And

537
00:21:35.560 --> 00:21:37.680
our sun is actually incredibly low

538
00:21:37.680 --> 00:21:39.920
variability compared to many stars.

539
00:21:40.400 --> 00:21:43.080
The solar cycle we observe is

540
00:21:43.080 --> 00:21:45.960
arguably a 22ish year cycle with

541
00:21:45.960 --> 00:21:48.600
two peaks and two minima. And the subtlety

542
00:21:48.600 --> 00:21:50.680
there is we get solar maximum when there are

543
00:21:50.680 --> 00:21:52.740
lots of sunspots, lots of activity, more

544
00:21:52.740 --> 00:21:55.300
aurora and solar minimum when we've got fewer

545
00:21:55.300 --> 00:21:57.660
sunspots, less activity, fewer aurora.

546
00:21:58.060 --> 00:22:00.700
And we get those on and about an 11 year

547
00:22:00.700 --> 00:22:02.860
cycle from one peak to the next, sometimes a

548
00:22:02.860 --> 00:22:05.300
bit shorter, sometimes a bit longer. But the

549
00:22:05.300 --> 00:22:08.260
origin of the solar cycles with the

550
00:22:08.260 --> 00:22:10.860
sun is the Sun's magnetic field. The sun

551
00:22:11.420 --> 00:22:13.340
has a magnetic field that runs from the North

552
00:22:13.340 --> 00:22:15.900
Pole to the South Pole. And it

553
00:22:15.900 --> 00:22:18.860
rotates in such a way that the rotation

554
00:22:18.860 --> 00:22:20.620
period at the equator and the rotation period

555
00:22:20.620 --> 00:22:22.900
at the poles are different rotates as a fluid

556
00:22:22.900 --> 00:22:25.200
body. So the time it takes the Sun's equator

557
00:22:25.200 --> 00:22:27.440
to rotate is a couple of days quicker than

558
00:22:27.440 --> 00:22:30.240
the poles. The magnetic field lines running

559
00:22:30.240 --> 00:22:32.480
from the North Pole to the South Pole get

560
00:22:32.480 --> 00:22:34.040
hooked up in the material and gradually get

561
00:22:34.040 --> 00:22:36.720
wound up a bit like an elastic band. And so

562
00:22:36.720 --> 00:22:38.600
the Sun's magnetic field gets more and more

563
00:22:38.600 --> 00:22:41.160
complicated through the 11 years, starts to

564
00:22:41.160 --> 00:22:42.800
get kinks and the kinks break through the

565
00:22:42.800 --> 00:22:44.760
surface. So you get locations where the

566
00:22:44.760 --> 00:22:46.400
magnetic field comes out of the surface,

567
00:22:46.400 --> 00:22:48.640
loops up and goes back down. And in the

568
00:22:48.640 --> 00:22:50.640
places where it's nearly vertical, it cools

569
00:22:50.640 --> 00:22:52.360
the surface of the sun because it suppresses

570
00:22:52.360 --> 00:22:53.690
convection of new energy from, from

571
00:22:53.690 --> 00:22:55.890
underneath, leading to cooler spots which

572
00:22:55.890 --> 00:22:58.410
look darker and therefore are sunspots. And

573
00:22:58.410 --> 00:22:59.930
gradually the sun gets more and more wound

574
00:22:59.930 --> 00:23:02.810
up. Sunspot activity begins at high latitudes

575
00:23:02.810 --> 00:23:04.530
and works its way down towards the equator

576
00:23:04.850 --> 00:23:07.010
and eventually around solar maximum, you get

577
00:23:07.010 --> 00:23:09.650
the field line starting to snap and break and

578
00:23:09.650 --> 00:23:12.290
you get a polar reversal happen. The north

579
00:23:12.290 --> 00:23:14.250
pole becomes a south pole and the south pole

580
00:23:14.250 --> 00:23:16.490
becomes a north pole and then it all begins

581
00:23:16.490 --> 00:23:18.690
again. So the reason we talk about a 22 year

582
00:23:18.690 --> 00:23:21.540
cycle is you get solar maximum

583
00:23:21.540 --> 00:23:23.380
with north pole to the north, well, north

584
00:23:23.380 --> 00:23:25.940
pole to the top, and then a minimum, then

585
00:23:25.940 --> 00:23:27.900
solar maximum with the south pole to the top,

586
00:23:27.900 --> 00:23:29.780
then a minimum, then you're back to where you

587
00:23:29.780 --> 00:23:32.780
started from. Roughly. Those

588
00:23:32.780 --> 00:23:35.380
cycles are driven by the magnetic activity of

589
00:23:35.380 --> 00:23:37.660
the sun and they vary the brightness of our

590
00:23:37.660 --> 00:23:39.660
star, um, by a vanishingly small amount. It's

591
00:23:39.660 --> 00:23:42.620
an incredibly stable star. I think you're

592
00:23:42.620 --> 00:23:44.460
talking about variability on the level, about

593
00:23:44.460 --> 00:23:47.310
one part in 2, 10,000, something

594
00:23:47.310 --> 00:23:49.390
like that. Now that is such a low level of

595
00:23:49.390 --> 00:23:51.670
variability that if we were observing an

596
00:23:51.990 --> 00:23:54.350
other star, we probably wouldn't be able to

597
00:23:54.350 --> 00:23:56.070
pick up the variability in the total

598
00:23:56.070 --> 00:23:58.310
brightness, but we would be able to pick up

599
00:23:58.310 --> 00:24:00.990
the magnetic activity. And this is magnetic

600
00:24:00.990 --> 00:24:03.870
activity. And star spots are uh, one of the

601
00:24:03.870 --> 00:24:05.790
challenges for people trying to find

602
00:24:05.790 --> 00:24:08.030
exoplanets because a star spot can mimic as

603
00:24:08.030 --> 00:24:10.150
an exoplanet and stellar activity like the

604
00:24:10.150 --> 00:24:13.150
Sun's magnetic cycle and the star. So SAR

605
00:24:13.150 --> 00:24:16.070
spots that go with it can actually be mimic

606
00:24:16.070 --> 00:24:17.910
a radial velocity planet. So there's a lot of

607
00:24:17.910 --> 00:24:20.350
work done in when we think we've got a signal

608
00:24:20.590 --> 00:24:22.350
confirming that it is actually a planet and

609
00:24:22.350 --> 00:24:24.550
not a star spot. So you've got that kind of

610
00:24:24.550 --> 00:24:25.310
stellar activity.

611
00:24:25.310 --> 00:24:28.230
Now most stars are significantly, uh, more

612
00:24:28.230 --> 00:24:29.830
variable than the sun. And there's a lot of

613
00:24:29.830 --> 00:24:31.950
other ways stars can vary. We think that

614
00:24:32.590 --> 00:24:35.070
most sun like stars will have sunspot cycles

615
00:24:35.070 --> 00:24:36.710
like the sun, and it's due to the structure

616
00:24:36.710 --> 00:24:39.590
of the convective and the radiative zones and

617
00:24:39.590 --> 00:24:41.310
all the rest of it. The internal structure of

618
00:24:41.310 --> 00:24:42.870
the sun, a bit like the Earth, has a crust, a

619
00:24:42.870 --> 00:24:45.550
mantle and a car. The magnetic field in the

620
00:24:45.550 --> 00:24:47.670
top layer of the sun can get tangled up.

621
00:24:49.030 --> 00:24:50.750
Stars of different masses have a bit of a

622
00:24:50.750 --> 00:24:52.630
different structure, but there's A lot of

623
00:24:52.790 --> 00:24:55.030
other ways that stars can be variable. And so

624
00:24:55.030 --> 00:24:57.270
we have a very wide variety of different

625
00:24:57.270 --> 00:24:59.670
types of variable stars. There are flare

626
00:24:59.670 --> 00:25:01.750
stars like Proxima Centauri, which have

627
00:25:02.070 --> 00:25:04.670
stellar activity that can occasionally be a

628
00:25:04.670 --> 00:25:06.310
super flare that can cause the star's

629
00:25:06.310 --> 00:25:07.870
brightness to change by almost a factor of

630
00:25:07.870 --> 00:25:10.110
100. And I normally talk about Proxima

631
00:25:10.110 --> 00:25:12.310
Centauri being 100 times too fancy with the

632
00:25:12.310 --> 00:25:14.950
naked eye, but in one mega flare it had a few

633
00:25:14.950 --> 00:25:16.430
years ago, it almost reached the edge of

634
00:25:16.430 --> 00:25:18.830
naked eye visibility. That flare was that

635
00:25:18.830 --> 00:25:21.550
intense. You've then got a, ah, large number

636
00:25:21.550 --> 00:25:23.590
of stars that vary in brightness. Bixa

637
00:25:23.590 --> 00:25:26.430
pulsate Bixa size changes fundamentally

638
00:25:26.910 --> 00:25:29.430
and usually these are stars coming towards

639
00:25:29.430 --> 00:25:30.630
the end of the life entering a bit of

640
00:25:30.630 --> 00:25:33.390
instability for various reasons. Some of them

641
00:25:33.390 --> 00:25:35.350
are only just moving off the main sequence or

642
00:25:35.350 --> 00:25:38.190
are very young. Others are super giant stars

643
00:25:38.190 --> 00:25:41.050
with different kinds of variability. But

644
00:25:41.050 --> 00:25:43.250
that variability causes their

645
00:25:43.890 --> 00:25:46.490
diameter to change, causes them to pulsate.

646
00:25:46.490 --> 00:25:47.690
And that's because they're just slightly out

647
00:25:47.690 --> 00:25:49.650
of equilibrium. When they're at their

648
00:25:49.650 --> 00:25:52.370
smallest they get hotter, they're putting out

649
00:25:52.370 --> 00:25:54.690
more energy because they're a bit hotter.

650
00:25:55.180 --> 00:25:57.850
Um, the surface layers therefore are pushed

651
00:25:57.850 --> 00:26:00.570
outwards with more force than gravity can

652
00:26:00.570 --> 00:26:02.970
push them in and they start to expand, they

653
00:26:02.970 --> 00:26:04.530
go through the equilibrium point but because

654
00:26:04.530 --> 00:26:06.770
they're still expanding they keep going. As

655
00:26:06.770 --> 00:26:08.890
the stars outer layers get bigger and bigger,

656
00:26:09.210 --> 00:26:12.050
the star cools. Because when you

657
00:26:12.050 --> 00:26:14.570
take a gas and you increase its volume,

658
00:26:14.810 --> 00:26:16.370
you lower the pressure and you lower the

659
00:26:16.370 --> 00:26:18.970
temperature so that material cools

660
00:26:19.210 --> 00:26:21.530
and eventually is giving out less energy

661
00:26:22.330 --> 00:26:25.090
than gravity pulling in would cause and it

662
00:26:25.090 --> 00:26:27.090
starts to collapse again. So instead of like

663
00:26:27.090 --> 00:26:29.130
the sun staying at that very fixed radius

664
00:26:29.130 --> 00:26:31.010
because gravity and radiation are balanced

665
00:26:31.010 --> 00:26:33.360
perfectly, you can get this oscillating

666
00:26:33.360 --> 00:26:34.960
behaviour where you overshoot in both

667
00:26:34.960 --> 00:26:37.240
directions. And um, sometimes that's fairly

668
00:26:37.240 --> 00:26:39.200
small, sometimes that's fairly large. And it

669
00:26:39.200 --> 00:26:41.240
happens at different phases of stars lives in

670
00:26:41.240 --> 00:26:43.960
different ways. One of the most famous types

671
00:26:43.960 --> 00:26:45.840
of variable stars are known as the Cepheid

672
00:26:45.840 --> 00:26:48.440
variable stars. And um, these are somewhat

673
00:26:48.440 --> 00:26:50.360
evolved stars coming towards the end of their

674
00:26:50.360 --> 00:26:52.880
life where the pulsation period

675
00:26:53.520 --> 00:26:56.480
is directly linked to how luminous a star is.

676
00:26:58.010 --> 00:27:00.450
So two similar stars, but one's brighter than

677
00:27:00.450 --> 00:27:03.050
the other intrinsically, put them at the same

678
00:27:03.050 --> 00:27:04.810
distance, one's more luminous, looks

679
00:27:04.810 --> 00:27:06.690
brighter, they will pulsate with different

680
00:27:06.690 --> 00:27:08.410
periods. And if you can measure the period,

681
00:27:08.970 --> 00:27:11.210
you can measure how luminous that star is.

682
00:27:11.370 --> 00:27:13.490
And that makes Cepheid variables an excellent

683
00:27:13.490 --> 00:27:16.050
step on our distance ladder. Because you see

684
00:27:16.050 --> 00:27:17.690
a star that's a certain Brightness, you don't

685
00:27:17.690 --> 00:27:19.810
really know how far away it is. But if you

686
00:27:19.810 --> 00:27:21.810
can measure the period of the Cepheid

687
00:27:21.810 --> 00:27:23.900
variable pulsating, that tells you

688
00:27:23.900 --> 00:27:26.020
intrinsically how luminous that star is,

689
00:27:26.660 --> 00:27:28.660
which means we can work out its distance. So

690
00:27:28.660 --> 00:27:29.620
they're really useful.

691
00:27:30.020 --> 00:27:32.740
Some stars are astonishingly variable.

692
00:27:33.040 --> 00:27:35.900
Um, among the stars with the biggest

693
00:27:35.900 --> 00:27:37.700
variation in brightness from brightest to

694
00:27:37.700 --> 00:27:40.260
faintest, um, are known as the Myra stars.

695
00:27:40.720 --> 00:27:43.100
Ah, Myra, the archetypal one is known as

696
00:27:43.100 --> 00:27:45.460
Myra, the wonderful Myra at its brightest

697
00:27:45.860 --> 00:27:48.700
is easily visible with a naked eye at

698
00:27:48.700 --> 00:27:50.900
its fantasy, you need a telescope to see it.

699
00:27:50.980 --> 00:27:52.500
And a few of these stars have

700
00:27:53.360 --> 00:27:54.960
amplitudes, the difference in brightness

701
00:27:54.960 --> 00:27:57.240
between the brightest and faintest that are

702
00:27:57.240 --> 00:27:58.760
such that they vary in brightness by more

703
00:27:58.760 --> 00:28:01.520
than a factor of 10,000. Um, a couple of

704
00:28:01.520 --> 00:28:04.040
examples here, Chi Cygni, which at its

705
00:28:04.040 --> 00:28:06.560
brightness is a magnitude 3.3 star, so

706
00:28:06.560 --> 00:28:08.120
comfortable with the naked eye, but not that

707
00:28:08.120 --> 00:28:10.360
bright at, ah, its Faintest is magnitude

708
00:28:10.360 --> 00:28:13.120
14.2. Um, that is

709
00:28:13.120 --> 00:28:16.040
a factor of about 25,000 in brightness

710
00:28:16.040 --> 00:28:18.400
between brightest and faintests. That is

711
00:28:19.110 --> 00:28:21.990
so long a period that that was discovered,

712
00:28:21.990 --> 00:28:24.550
that variability back in 1686.

713
00:28:25.110 --> 00:28:27.430
You've got a wide variety of mirror type

714
00:28:27.430 --> 00:28:29.390
stars dominating the stars with the biggest

715
00:28:29.390 --> 00:28:31.750
variability. But there are other type ones in

716
00:28:31.750 --> 00:28:34.629
there. Arcarona Borealis is a famous one in

717
00:28:34.629 --> 00:28:36.990
the bowl of the northern crown, normally only

718
00:28:36.990 --> 00:28:39.630
barely visible with the naked eye. So carbon

719
00:28:39.630 --> 00:28:42.150
star, where the mirror stars

720
00:28:42.550 --> 00:28:44.710
have a periodic variation, they're pulsating

721
00:28:44.710 --> 00:28:47.150
in a broadly periodic way with periods of a

722
00:28:47.150 --> 00:28:49.650
year or more. Acherona

723
00:28:49.650 --> 00:28:51.370
Borealis is different. It shines along,

724
00:28:51.370 --> 00:28:52.890
shines along, shines along and then suddenly

725
00:28:52.890 --> 00:28:54.250
it's like somebody drops a curtain in front

726
00:28:54.250 --> 00:28:57.050
of it and its brightness plunges and then it

727
00:28:57.050 --> 00:28:59.250
gradually brightens up again. And that is not

728
00:28:59.250 --> 00:29:01.930
exactly periodic. It's known as a carbon

729
00:29:01.930 --> 00:29:03.960
star. And what's happening is that, ah,

730
00:29:03.960 --> 00:29:05.770
occasionally it's got a huge amount of carbon

731
00:29:05.770 --> 00:29:08.170
in its atmosphere. Occasionally the carbon

732
00:29:08.170 --> 00:29:10.330
condenses into soot, blocking the light from

733
00:29:10.330 --> 00:29:12.610
underneath. That cools the outer layers,

734
00:29:12.610 --> 00:29:14.490
which gets this runaway condensation of

735
00:29:14.490 --> 00:29:16.810
carbon carbon into soot. That traps the

736
00:29:16.810 --> 00:29:19.210
radiation from inside, so the heat builds up

737
00:29:19.210 --> 00:29:20.850
inside until eventually the carbon gets

738
00:29:20.850 --> 00:29:22.970
turned back into a gas again. The clouds

739
00:29:22.970 --> 00:29:24.330
clear and the star brightens again.

740
00:29:24.650 --> 00:29:26.610
Andrew Dunkley: So that's, I was, I was just going to

741
00:29:26.610 --> 00:29:28.570
stupidly suggest that it was soot.

742
00:29:28.650 --> 00:29:31.610
Jonti Horner: Yeah, it is, it's a carbon star. And a Corona

743
00:29:31.610 --> 00:29:34.290
Borealis is the archetypal, most

744
00:29:34.290 --> 00:29:36.490
famous one. It's described as a low mass

745
00:29:36.490 --> 00:29:38.290
yellow supergiant. So again, it's a star

746
00:29:38.290 --> 00:29:39.850
coming towards the end of its life,

747
00:29:40.640 --> 00:29:43.580
um, every so often can be after just

748
00:29:43.580 --> 00:29:45.980
a few months, or it can be a few years. It

749
00:29:45.980 --> 00:29:48.260
can dim by as much as a factor of 10,000

750
00:29:48.500 --> 00:29:51.220
because it kind of suits up, clouds up.

751
00:29:51.460 --> 00:29:53.300
And if you look at the light curve of that.

752
00:29:53.300 --> 00:29:54.940
If you're bored, have a look at the light

753
00:29:54.940 --> 00:29:57.780
curve on Wikipedia, because it's really

754
00:29:57.780 --> 00:29:59.980
head scratching. It shows you how random this

755
00:29:59.980 --> 00:30:01.980
is and how hard it must have been for people

756
00:30:01.980 --> 00:30:04.780
to understand. Um, there was an incredible

757
00:30:04.780 --> 00:30:06.860
deep minimum that happened in the, the

758
00:30:06.860 --> 00:30:09.660
mid-2010s, I think it was, where it

759
00:30:09.660 --> 00:30:11.700
dimmed and then it stayed dim for ages.

760
00:30:12.020 --> 00:30:13.780
Normally it's bright and then it dims for a

761
00:30:13.780 --> 00:30:15.460
bit and then it brightens up fairly quickly.

762
00:30:16.260 --> 00:30:19.020
But fundamentally, there's a huge variety of

763
00:30:19.020 --> 00:30:21.940
ways in which stars can vary intrinsically

764
00:30:21.940 --> 00:30:24.860
themselves. Their brightness can vary. It

765
00:30:24.860 --> 00:30:27.300
is known from discussions with the

766
00:30:27.300 --> 00:30:28.540
traditional owners of the land here in

767
00:30:28.540 --> 00:30:30.300
Australia that the variability of

768
00:30:30.300 --> 00:30:32.180
Beetlejuice, Nal, Deborah, and two bright red

769
00:30:32.180 --> 00:30:34.760
giant, giant red supergiant stars in our

770
00:30:34.760 --> 00:30:37.520
summer sky, Northern Hemisphere winter sky,

771
00:30:37.760 --> 00:30:39.480
are variable. We saw that with the great

772
00:30:39.480 --> 00:30:41.640
dimming of Beetlejuice about a decade ago.

773
00:30:41.640 --> 00:30:44.080
Now, that kind of variability has been known

774
00:30:44.080 --> 00:30:46.000
for hundreds, if not thousands of years among

775
00:30:46.080 --> 00:30:48.280
traditional owners around the world who look

776
00:30:48.280 --> 00:30:50.960
at the night sky so that stars

777
00:30:50.960 --> 00:30:53.320
varying intrinsically in brightness, the star

778
00:30:53.320 --> 00:30:56.120
itself varying. And, um, it's a wonderful

779
00:30:56.120 --> 00:30:57.920
rabbit hole for people to wander down. It's

780
00:30:57.920 --> 00:30:59.760
another area of astronomy where amateur

781
00:30:59.760 --> 00:31:02.470
astronomy contribute a lot because there's

782
00:31:02.470 --> 00:31:04.510
very active variable star observers who will

783
00:31:04.510 --> 00:31:05.910
go out there and measure the brightness of

784
00:31:05.910 --> 00:31:08.110
stars repeatedly to track when they vary.

785
00:31:08.670 --> 00:31:10.910
We get a lot of that knowledge. You've then

786
00:31:10.910 --> 00:31:12.870
got a second type of stellar variability

787
00:31:12.870 --> 00:31:15.870
which is not intrinsic, but is extrinsic.

788
00:31:15.870 --> 00:31:18.110
What I mean by that is an intrinsically

789
00:31:18.110 --> 00:31:20.990
variable star is a star itself changing. An

790
00:31:20.990 --> 00:31:23.590
extrinsic variation is something else causing

791
00:31:23.590 --> 00:31:25.750
the brightness of the star to change. You

792
00:31:25.750 --> 00:31:27.310
know, put your hand in front of the star. The

793
00:31:27.310 --> 00:31:28.430
stars dissipate because your hand's

794
00:31:28.430 --> 00:31:31.110
absorbing. All the lights disappeared. We

795
00:31:31.110 --> 00:31:33.390
have multiple star systems where we have

796
00:31:33.390 --> 00:31:36.270
eclipsing binaries. Algol is possibly the

797
00:31:36.270 --> 00:31:38.310
most famous of these. The winking demon star,

798
00:31:38.630 --> 00:31:40.790
whose brightness drops by about a factor of

799
00:31:40.790 --> 00:31:43.630
three every couple of days. And that

800
00:31:43.630 --> 00:31:46.070
star is bright enough to be easily visible

801
00:31:46.070 --> 00:31:48.310
with the naked eye. And, um, the

802
00:31:48.470 --> 00:31:50.750
variability in its brightness is sufficiently

803
00:31:50.750 --> 00:31:52.830
large that it's easily noticeable with the

804
00:31:52.830 --> 00:31:55.830
naked eye. So its brightness varies. I

805
00:31:55.830 --> 00:31:57.840
think it's every 70 hours or so. I just want

806
00:31:57.840 --> 00:31:59.520
to cheque it out. Um,

807
00:32:01.000 --> 00:32:03.720
no, it's less often Than that. Algol's

808
00:32:03.720 --> 00:32:06.680
brightness varies every 2.86 days.

809
00:32:07.640 --> 00:32:10.640
So every 2.86 days, the brightness of

810
00:32:10.640 --> 00:32:13.240
the star drops from magnitude 2.1 to 3.4.

811
00:32:13.240 --> 00:32:15.240
That's a brightness change of about a factor

812
00:32:15.240 --> 00:32:18.160
of three times, roughly. And, uh, it dims for

813
00:32:18.160 --> 00:32:20.280
about 10 hours and then brightens up again.

814
00:32:20.840 --> 00:32:23.200
Became known as a winking demon star that has

815
00:32:23.200 --> 00:32:26.040
been known to be variable since prehistory.

816
00:32:26.040 --> 00:32:29.000
In reality, there's allegations

817
00:32:29.000 --> 00:32:31.080
that perhaps an Egyptian calendar that talked

818
00:32:31.080 --> 00:32:32.840
about unlucky days may have been linked to

819
00:32:32.840 --> 00:32:35.680
that. That's questionable. Where it is

820
00:32:35.680 --> 00:32:37.120
really interesting, though, is the

821
00:32:37.520 --> 00:32:40.400
variability of Algol was first explained

822
00:32:40.720 --> 00:32:43.480
by John Goodrich, who is one of

823
00:32:43.480 --> 00:32:45.480
those heroes of astronomy you don't hear

824
00:32:45.480 --> 00:32:47.680
about very often, mainly because he lived a

825
00:32:47.680 --> 00:32:50.160
very short life. He presented findings in May

826
00:32:50.750 --> 00:32:53.670
1783 to suggest that the

827
00:32:53.670 --> 00:32:55.790
variability, the periodic variability of

828
00:32:55.790 --> 00:32:58.470
Algol was caused by a dark body or a dimmer

829
00:32:58.470 --> 00:33:01.390
body passing in front of it every 2.86 days.

830
00:33:01.790 --> 00:33:04.430
He was awarded a medal for this, I believe.

831
00:33:04.430 --> 00:33:06.509
He never got to receive the medal because he

832
00:33:06.509 --> 00:33:09.350
died, as I say, very, very young. Died at the

833
00:33:09.350 --> 00:33:12.030
age of 21. Got the Copley Medal in

834
00:33:12.030 --> 00:33:14.870
1783, I think he was. Uh, passed away

835
00:33:14.870 --> 00:33:17.150
three years after that. So in just 21 years

836
00:33:17.150 --> 00:33:20.110
old, he contributed hugely to our modern

837
00:33:20.110 --> 00:33:22.670
knowledge of variable stars. And, um, you

838
00:33:22.670 --> 00:33:24.070
know, it's very unfortunate that he passed

839
00:33:24.070 --> 00:33:26.990
away at such a young age, but he was able to

840
00:33:26.990 --> 00:33:28.950
explain this variability that had been

841
00:33:28.950 --> 00:33:30.710
clearly known for a very long time. It's

842
00:33:30.710 --> 00:33:32.590
obvious to the naked eye that this star gets

843
00:33:32.590 --> 00:33:35.470
dimmer. It's not a subtle effect, but he

844
00:33:35.470 --> 00:33:37.350
was the one who was able to explain it.

845
00:33:38.630 --> 00:33:41.110
Despite his challenges. He was someone with

846
00:33:41.350 --> 00:33:44.310
certain physical disabilities. He was someone

847
00:33:44.310 --> 00:33:46.680
who had a very difficult life. But he had

848
00:33:46.680 --> 00:33:48.560
such a visionary intellect at the time to

849
00:33:48.560 --> 00:33:50.720
come up with the explanation that this

850
00:33:50.720 --> 00:33:52.920
periodic variability and the style of it and

851
00:33:52.920 --> 00:33:55.000
the frequency and the depth of it being so

852
00:33:55.000 --> 00:33:57.760
repeatable was because this was actually

853
00:33:57.840 --> 00:34:00.560
two objects going around each other. Ties in

854
00:34:00.560 --> 00:34:02.160
with the exoplanet chat we had earlier,

855
00:34:02.320 --> 00:34:04.480
because in a way, this is the indirect

856
00:34:04.640 --> 00:34:07.120
discovery of the binarity of Algol.

857
00:34:07.520 --> 00:34:09.160
You don't know that there are two stars there

858
00:34:09.160 --> 00:34:10.960
because you t two stars separately. They're

859
00:34:10.960 --> 00:34:13.239
circles close together. You can't separate

860
00:34:13.239 --> 00:34:16.079
them with telescopes, modular, hugely massive

861
00:34:16.079 --> 00:34:18.399
interferometers we have today. But you can

862
00:34:18.399 --> 00:34:20.919
infer the two stars there by the

863
00:34:20.919 --> 00:34:23.439
extrinsic variability, the variability of the

864
00:34:23.439 --> 00:34:25.439
light we receive because one blocks light

865
00:34:25.439 --> 00:34:28.199
from the other, fundamentally. So that also

866
00:34:28.919 --> 00:34:31.599
causes cyclical variations in

867
00:34:31.599 --> 00:34:33.199
brightness. But it's not the star in this

868
00:34:33.199 --> 00:34:36.199
case varying. It's a result of the

869
00:34:36.199 --> 00:34:38.039
environment around the star blocking some of

870
00:34:38.039 --> 00:34:38.289
the light.

871
00:34:39.640 --> 00:34:42.120
Andrew Dunkley: Yeah. Okay, so the answer to

872
00:34:42.120 --> 00:34:44.320
Casey's questions are, uh, fundamentally,

873
00:34:44.320 --> 00:34:46.129
yes, um,

874
00:34:46.840 --> 00:34:49.680
stars. Most stars probably have some sort of

875
00:34:49.680 --> 00:34:52.480
variability, some more than others. Uh, the

876
00:34:52.480 --> 00:34:55.240
solar cycles are caused by the buildup

877
00:34:55.240 --> 00:34:57.800
of, um, activity

878
00:34:59.000 --> 00:35:01.920
and um. Yeah. Does every type of

879
00:35:01.920 --> 00:35:03.400
star go through solar cycling?

880
00:35:03.400 --> 00:35:05.220
Jonti Horner: Probably. Does it? It's one of. Like I said,

881
00:35:05.220 --> 00:35:06.540
it's one of the big challenges for us with

882
00:35:06.540 --> 00:35:08.420
our radial velocity work. Looking for planet

883
00:35:08.420 --> 00:35:11.260
trans is filtering out the stellar

884
00:35:11.260 --> 00:35:12.820
cycles and that's particularly a problem for

885
00:35:12.820 --> 00:35:14.740
finding planets like Jupiter on a Jupiter

886
00:35:14.740 --> 00:35:17.020
like orbit. Jupiter goes around the sun every

887
00:35:17.020 --> 00:35:19.820
11.86 years. The solar cycle is about

888
00:35:19.820 --> 00:35:22.780
11 years. It's m hard to disentangle the two.

889
00:35:23.180 --> 00:35:25.860
There's also a fascinating branch of science

890
00:35:25.860 --> 00:35:27.660
and one of my colleagues at Uni SQ is one of

891
00:35:27.660 --> 00:35:29.660
the world's experts in this. Um, Professor

892
00:35:29.660 --> 00:35:32.400
Simon Murphy. This is a discipline called

893
00:35:32.400 --> 00:35:35.160
asteroseismology. We know about the

894
00:35:35.160 --> 00:35:37.560
Earth's interior because of earthquakes. We

895
00:35:37.560 --> 00:35:39.120
can figure out the crust, the core, the

896
00:35:39.120 --> 00:35:41.200
mantle by how different types of seismic

897
00:35:41.200 --> 00:35:43.240
waves pass through the Earth's interior. So

898
00:35:43.240 --> 00:35:44.920
we'll listen to the Earth ringing like a bell

899
00:35:44.920 --> 00:35:46.439
after an earthquake and we can use that

900
00:35:46.439 --> 00:35:48.840
information to sense what the interior

901
00:35:48.840 --> 00:35:51.440
structure is and how it varies. The science

902
00:35:51.440 --> 00:35:53.680
of astroseismology is doing the same kind of

903
00:35:53.680 --> 00:35:55.480
thing with stars, looking at how they wibble

904
00:35:55.480 --> 00:35:58.150
and wobble to map out their interior and

905
00:35:58.150 --> 00:35:59.910
understand it. And that's fundamentally tied

906
00:35:59.910 --> 00:36:02.350
to the variability. Now Simon's got a couple

907
00:36:02.350 --> 00:36:04.430
of PhD students working with him and doing

908
00:36:04.430 --> 00:36:06.830
some fabulous work, um, including

909
00:36:07.790 --> 00:36:09.350
Guy, um, called Tom Love, who's down in New

910
00:36:09.350 --> 00:36:10.950
Zealand, who's an amateur astronomer there,

911
00:36:10.950 --> 00:36:13.390
doing a PhD, just finishing up with us. Where

912
00:36:13.390 --> 00:36:15.590
they're looking with Simon at these

913
00:36:15.590 --> 00:36:18.270
asteroseismology, wibbly wobbliness and also

914
00:36:18.270 --> 00:36:20.950
at the variability of stars. Looking

915
00:36:20.950 --> 00:36:23.670
at a group of stars called the Delta Scuti

916
00:36:23.670 --> 00:36:25.740
stars, which are a particular type of

917
00:36:25.740 --> 00:36:28.380
oscillating, varying vibrating

918
00:36:28.460 --> 00:36:31.340
star, looking at how their interiors behave,

919
00:36:31.340 --> 00:36:33.500
looking at how old they are. So we can better

920
00:36:33.500 --> 00:36:36.060
understanding of the physics going on and a

921
00:36:36.060 --> 00:36:38.380
better understanding of where these stars sit

922
00:36:38.380 --> 00:36:41.060
in the storey of stellar lives. So this kind

923
00:36:41.060 --> 00:36:44.020
of question is one that leads

924
00:36:44.020 --> 00:36:46.380
to whole, uh, rafts of amazing science that's

925
00:36:46.380 --> 00:36:47.700
been done. And I think like everything we

926
00:36:47.700 --> 00:36:50.140
discuss on the show, these questions are all,

927
00:36:50.290 --> 00:36:52.290
all entryways to rabbit holes that can go as

928
00:36:52.290 --> 00:36:53.170
deep as you want to.

929
00:36:54.290 --> 00:36:57.290
Andrew Dunkley: Yes, absolutely. There you are,

930
00:36:57.290 --> 00:36:59.070
Casey. Thanks for the question, really, uh,

931
00:36:59.370 --> 00:37:01.690
really interesting. And um, yeah, it's

932
00:37:01.690 --> 00:37:02.170
fascinating.

933
00:37:02.170 --> 00:37:04.730
Stars. I, I've been spending a lot of time

934
00:37:04.730 --> 00:37:07.570
outside of my telescope recently, uh, and

935
00:37:07.970 --> 00:37:09.970
photographing where I can

936
00:37:11.170 --> 00:37:13.410
some of the, the big stars that are visible.

937
00:37:13.550 --> 00:37:16.410
Um, um, I think I did I get serious

938
00:37:16.410 --> 00:37:18.610
recently. I can't remember. I've got a couple

939
00:37:18.610 --> 00:37:20.330
of good ones. I got Alpha Centauri the other

940
00:37:20.330 --> 00:37:23.270
night, which turned out really well. Uh, but

941
00:37:23.270 --> 00:37:24.950
yeah, thanks for the question, Casey. If you

942
00:37:24.950 --> 00:37:27.030
have questions for us, please send them in

943
00:37:27.030 --> 00:37:29.950
via our website spacenutspodcast.com

944
00:37:30.350 --> 00:37:32.590
and click on the Ask me anything button at

945
00:37:32.590 --> 00:37:35.070
the top. It's labelled ama. You can leave

946
00:37:35.150 --> 00:37:37.310
text or audio messages. If you've got a

947
00:37:37.310 --> 00:37:39.030
device with a microphone, you're all set.

948
00:37:39.030 --> 00:37:41.550
Such as a, I don't know, cell phone, mobile

949
00:37:41.550 --> 00:37:44.550
phone, um, tablet, anything like that.

950
00:37:44.550 --> 00:37:47.360
Or your computer. The got built in mics

951
00:37:47.360 --> 00:37:49.560
these days and just tell us who you are and

952
00:37:49.560 --> 00:37:51.040
where you're from and we'd be happy to try

953
00:37:51.040 --> 00:37:53.920
and solve your riddles. Uh, and have a

954
00:37:53.920 --> 00:37:55.160
look around while you're there. Cheque out

955
00:37:55.160 --> 00:37:56.960
the shop. Cheque out. Uh, Astronomy

956
00:37:56.960 --> 00:37:58.600
AstroDailyPod. Maybe sign up for your daily

957
00:37:58.600 --> 00:38:01.240
feed of astronomical news and

958
00:38:01.320 --> 00:38:03.360
click the supporter tab if you'd like to help

959
00:38:03.360 --> 00:38:06.360
us out. That is totally optional. Uh, and

960
00:38:06.360 --> 00:38:08.200
thank you Jonty for all your help today.

961
00:38:08.360 --> 00:38:09.800
Jonti Horner: Absolute pleasure. It's always good to have a

962
00:38:09.800 --> 00:38:10.120
chat.

963
00:38:10.680 --> 00:38:12.910
Andrew Dunkley: We'll see you soon when we talk, uh,

964
00:38:12.910 --> 00:38:15.280
Astrobiology Part two.

965
00:38:15.770 --> 00:38:17.960
Uh, that is Professor Johnty Horner from the

966
00:38:17.960 --> 00:38:20.950
University of Southern Queensland. And uh,

967
00:38:20.950 --> 00:38:23.160
thanks to Huw in the studio, couldn't uh, be

968
00:38:23.160 --> 00:38:26.160
with us today? Huw? Um, he's an ex radio

969
00:38:26.160 --> 00:38:28.160
guy so he thinks he's a star,

970
00:38:28.970 --> 00:38:31.440
uh, which means his equator rotates more than

971
00:38:31.440 --> 00:38:33.200
his north and south and he's back in hospital

972
00:38:33.200 --> 00:38:36.120
with a twisted bow. And from me, Andrew

973
00:38:36.120 --> 00:38:38.960
Dunkley. Terrible. Thanks for your company.

974
00:38:38.960 --> 00:38:40.680
We'll catch you on the next episode of Space

975
00:38:40.680 --> 00:38:41.840
Network Nuts. Bye bye.

976
00:38:43.120 --> 00:38:45.400
Jonti Horner: You've been listening to the Space Nuts

977
00:38:45.400 --> 00:38:48.360
podcast available at

978
00:38:48.360 --> 00:38:50.320
Apple Podcasts, Spotify,

979
00:38:50.560 --> 00:38:53.280
iHeartRadio or your favourite podcast

980
00:38:53.280 --> 00:38:55.000
player. You can also stream on

981
00:38:55.000 --> 00:38:56.640
demand@bytes.com.

982
00:38:57.040 --> 00:38:59.080
Andrew Dunkley: this has been another quality podcast

983
00:38:59.080 --> 00:39:01.200
production from bytes.com.