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  1. jutfrank's Avatar
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    #11

    Re: The biggest of the smallest

    Here you go:

    Quote Originally Posted by Glizdka View Post
    Stars can be divided into two groups: small stars that can only support the basic type of nuclear fusion which converts hydrogen into helium, and big stars that are massive enough to achieve a more advanced type of fusion which allows them to further convert helium into heavier elements. Yawn. That's a mouthful of an introductory sentence. It's very clear but I'm already very slightly taxed right from the get-go. Try either to shorten it or split it. Better still, preface it with something sexier.

    Our star, the Sun, falls into the
    small group as it's too small to support the latter type of fusion. At the same time, the Sun is one of the biggest representatives of its group; it's in the top 10% of stars in terms of its mass, just a bit shy of falling into the big group. I'm questioning the numbers here. I'm thinking to myself "In the top 10%? That makes it seem big, but you're saying it's small. Have I understood that right? I'd better read the sentence again, to make sure I haven't misunderstood." Save me from doing this by making this apparent contradiction clearer.

    In this article, you will learn what it means for the Sun to be "the biggest of the smallest", and what would happen if it were just a bit bigger. Although it is generally a good idea to signpost learning outcomes, I don't think it suits the genre of this text very well. It sounds too teacherly.

    Let's start Again, very teacherly. Are you sure that's the writer-reader relationship you want? with what it means to be a small star. The stars in this group vary in mass widely. It's obvious to you that by 'small', you're talking about mass, but an average lay reader like me is thinking about size. How about addressing this? It is crucial to the whole idea of the piece, after all. The smallest of them can barely support any type of fusion at all, slowly burning like an ember over trillions of years. You might think that the ones in the middle of this group should last longer because they are more massive and have more fuel to burn through, but the contrary is true. They are better at sustaining nuclear fusion, and burn through their fuel much faster, over just billions of years, until they eventually run out of it and extinguish.

    The biggest stars in the small group, like our sun, are a different story. Over their lifetime, they accumulate helium in their cores which makes them denser, more compact. Locally, the denser core behaves as if its star were heavier. Odd sentence. I had to re-read it. Locally? Fusion speeds up, more helium is produced in the core, the core gets even denser, fusion speeds up even more. They get hotter and hotter the older they are Change this to over time until, eventually, near the end of their lifetime, the second type of fusion can trigger inside their cores. They start fusing helium into heavier elements, their temperature rises immensely, they swell, get bloated, and become what we call red giants.

    The Sun will get there When? How long have we got? I must know!; its diameter will increase so much it will engulf the Earth. Cool. Um, I mean Oh, no! However, by the time the cores of stars like our sun get dense enough to support the second type of fusion, they will have already used up almost all of their fuel, and won't last very long like that. The core will soon turn off, and the bloated outer layer will pop. Okay, this is good because you're finally giving me something I can easily visualise, and something dramatic at that. It's not easy (and not much fun) to imagine nuclear fusion.

    As for the big stars, the second type of fusion triggers much earlier in their lifetime. For the biggest of them, it starts from the get go. They burn through their fuel fast, for some within less than a million years. They are hot, bright, and dangerous. The smallest of them get to the red giant phase much earlier than our sun will, and they stay like that much longer. When the core turns off, the bloated outer layer gets catapulted into space in one last violet burst of nuclear energy. Nice. Again, that's fun to imagine.

    The biggest of the biggest are truly scary. Ooh! That sounds exciting. Fusion accelerates so fast for them that they don't get a chance to become the giants. On top of that, their immense gravity crushes against the outwards pressure from the core so heavily that it disallows them to expand. When the core finally turns off, and the outwards pressure from nuclear fusion is no more, all their mass gets pulled inwards, crashing into the core - they implode. All what's left fuses in an instant, creating unimaginable amounts of energy. There's no force in the universe that would hold it; the star rips itself apart in a cataclysmic explosion known as the supernova. Wow! You've totally got me here.

    If our sun were just a bit bigger, it would become one of the big stars, a monster that would quickly and effortlessly kill all life on Earth before it could get enough time to produce complex organisms, such as ourselves. Perhaps you could tell me which group some of my fave stars fall into. Betelgeuse is a big one, right? How about our neighbours? Proxima Centauri? The Sun, the biggest of the smallest stars, is safe to live around... for now.
    Nice ending, but you didn't say how long we've got. I still have that novel to finish!
    Last edited by jutfrank; 05-Jun-2020 at 03:46.

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    #12

    Re: The biggest of the smallest

    Quote Originally Posted by Tarheel View Post
    Each element is more stable than the previous one.
    Thanks for help, Tarheel. I thought it wouldn't be clear without next.

    I talked about stability because I thought it would be imaginative enough for the reader to get the gist of what I'm referring to, without the need to introduce the subject of binding energy. The problem with describing how binding energy affects stellar fusion is that binding energy per nucleon, when plotted on a graph, produces a line with a peculiar shape.



    There's a "gap" between helium and carbon that is responsible for stopping nuclear fusion in smaller stars. Then, it rises until it reaches iron, where nuclear fusion stops for all stars. Then, it falls, making fusion impossible unless in a cataclysmic event where everything fuses at once. I didn't even want to bother the reader with the fact that elements with an uneven number of protons are always less stable than neighboring elements with an even number of protons.

    Do you think From carbon (12) to iron (56), each element is more stable than the previous one is clear enough, even though grossly simplified?

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    #13

    Re: The biggest of the smallest

    Thanks for your help, Frank. These comments really help me get the idea of what I'm doing wrong with my writing. I'll apply them in the third version of the text.

    Perhaps you could tell me which group some of my fave stars fall into. Betelgeuse is a big one, right? How about our neighbours? Proxima Centauri?
    I'm sorry to say it, but our sun is a tiny pimple in the universe, even though it's in the top 10%. Virtually everything you can see in the night sky is a big star. I should've put that in the text.

    Betelgeuse is/was definitely big. (depending on whether it's already gone)
    Proxima is the pimplest of pimples.

    When? How long have we got? I must know!
    Some 3 billion years before it's time we got out of here. I'm sure we'll have more immediate problems in the meantime.
    Last edited by Glizdka; 05-Jun-2020 at 04:28.

  4. jutfrank's Avatar
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    #14

    Re: The biggest of the smallest

    Quote Originally Posted by Glizdka View Post
    Virtually everything you can see in the night sky is a big star. I should've put that in the text.
    Yes. Exploit the limited knowledge that the average reader already has.

    Some 3 billion years before it's time we got out of here.
    I have a strangely vivid memory from when I was around 10 or 11. My nerdy and very bright schoolfriend Guy Stockwell was round at my house. I was killing a break of probably 27 on my 6' x 3' kids' pool table while Guy was casually, and rather precociously, reading a New Scientist article about the death of the sun. Guy looks up, grinning, and says "We've only got another 1.1. billion years". It's funny how things like that stay with you. Ever since then, I've always repeated what he told me.

    I'm sure we'll have more immediate problems in the meantime.
    Right—like finally finishing that novel!

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    #15

    Re: The biggest of the smallest

    Quote Originally Posted by jutfrank View Post
    I have a strangely vivid memory from when I was around 10 or 11. My nerdy and very bright schoolfriend Guy Stockwell was round at my house. I was killing a break of probably 27 on my 6' x 3' kids' pool table while Guy was casually, and rather precociously, reading a New Scientist article about the death of the sun. Guy looks up, grinning, and says "We've only got another 1.1. billion years". It's funny how things like that stay with you. Ever since then, I've always repeated what he told me.
    As usual, it's "more complicated than that".

    It depends on the question. Are you interested when the Sun will engulf the Earth, the ultimate apocalypse? Are you interested in when it starts spewing thousands of Earth's mass worth of material in Earth's general direction on a regular basis? Are you interested in when it's too hot to live around?

    There are many problems we could solve and live around our star even though it's already become dangerous. In 1 billion years, the Sun will be just hot enough to cause mass extinction and a major change in the geology of Earth, but I think we'll manage. I see no way of surviving around Sun in 3 billion years, even theoretically, unless we find a way to build a forcefield around Earth, but that's a whole different story.

  6. jutfrank's Avatar
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    #16

    Re: The biggest of the smallest

    Well, there will be no 'we' in any familiar sense in a billion years, let alone three, so I don't suppose it matters much. I can imagine that terrestrial life of any kind will have been long extinct by that time.

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    #17

    Re: The biggest of the smallest

    Quote Originally Posted by jutfrank View Post
    Well, there will be no 'we' in any familiar sense in a billion years, let alone three, so I don't suppose it matters much. I can imagine that terrestrial life of any kind will have been long extinct by that time.
    You're probably right. I think the Earth has more to worry about from humans than from its star.

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    #18

    Re: The biggest of the smallest

    Try:

    will eventually overload its fusing capacity, use up all its fuel and end in a supernova.

    Not a professional teacher

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    #19

    Re: The biggest of the smallest

    Quote Originally Posted by Glizdka View Post
    You're probably right. I think the Earth has more to worry about from humans than from its star.
    I don't think Earth has nothing to to fear from us. It will be here long after we are gone. (Not to mention that what with hurricanes, tsunamis, earthquakes and volcanoes, the planet is always trying to kill us. )
    Not a professional teacher

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    #20

    Re: The biggest of the smallest

    Quote Originally Posted by Tarheel View Post
    I don't think Earth has nothing to to fear from us.
    Unless you mean that Earth actually does have something to fear from us (the rest of your post suggests that's not what you mean), then I assume you intended to write either "I don't think Earth has anything to fear ..." or "I think Earth has nothing to fear ...".
    Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.

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