The biggest of the smallest

[Glizdka]

Writing this article is meant to test my ability to use English to explain a scientific topic comprehensively, such that you understand the idea. The text should meet all your teacherly standards; please tell me if it doesn't. ;-) In this article, I will explain why I think the star Sun is "the biggest of the smallest", and also why iron is the perfect element.

---

Our star is a G2 class star. This means that it's somewhere in the middle of stellar classification, that classifies stars by color and temperature, closer to the low end. (↑OBAF[G]KM↓) If the Sun were more massive, it could sustain the CNO cycle, and become an F class star. The CNO cycle is revolutionary in stellar evolution because it allows stars a quick and spectacular life the Sun will never have; it will live a long and peaceful life among many other stars too small to sustain it. The Sun isn't small when compared to other stars, though, as it is in the top 10% of stars in terms of mass; it's just that it takes a lot of mass to sustain the cycle.

The CNO cycle allows nuclear fusion to produce elements heavier than hydrogen and helium, which is all other elements. Stars like our sun use the gravity from their mass to squash hydrogen inside. This process splices hydrogen, and makes it fuse into helium, but helium is where it stops for such small stars. Only bigger, more massive stars can go further, from helium to carbon, nitrogen, and oxygen, hence the name, the CNO cycle. Once the cycle is sustainable, there's no return; the star is on its way to a positive feedback loop that will eventually overload its fusing capacity, use up all its fuel, and end it in a supernova.

Not all configurations of matter are equally stable. Helium has four nucleons closely packed together inside its core, a more stable configuration than if the four nucleons were separate. Higher stability of an atom means that less energy is required to hold its core together, and that energy can be released if we transform an atom into another, more stable. That's how the Sun extracts energy from hydrogen in nuclear fusion. However, adding more nucleons would produce lithium, beryllium, and boron, all of which are less stable than helium, and the product would only quickly fall apart back into the subtracts. This is where fusion cannot progress any further, unless the star has a strong enough gravitational pull to squash twelve nucleons together in short time, producing carbon.

Carbon is the first on the list of elements more stable than helium; Nitrogen and Oxygen are next. The CNO cycle is more efficient than fusing hydrogen into helium, and once sustainable, becomes the predominant source of nuclear energy for the star. The CNO cycle is the first step towards fusing iron, the most stable element in terms of binding energy of a nucleon configuration. From carbon (12) to iron (56), each next element is more stable than the previous one, meaning that fusing these elements will allow for releasing energy. Past iron, each next element is less stable, and fissioning them, rather than fusing, is the way to release energy. This is what makes heavy, unstable elements like uranium good fissile but terrible fusile materials. Once fusion reaches iron, it's reached its limit, and the star is on its way to death, the fate our star will not share, luckily.

 

[jutfrank]

Allow me to comment:

I find the content of the piece very interesting but I have trouble with the organisation. It strikes me as more than a little messy, which makes it hard-going to follow.

I'm wondering whether if I gave these four paragraphs to a C1 class as a jigsaw reading exercise they would order them in the same sequence as you have them. I'm not sure they would. I think paragraph 1 (P1) makes more sense after P2, for example.

With how much detail did you plan each paragraph before you started writing? How about discourse linkers? How much did you consciously consider those? I can't see much evidence of that. Where exactly are the connectors (whether they be grammatical, lexical, logical, stylistic or whatever) that link the paragraphs/ideas together coherently?

If you were a teacher, assessing this for cohesion and coherence, what comments would you make? Think about what exactly the function of each paragraph is, and how exactly the content relates to the previous/following one, and also to the text as a whole.

 

[Glizdka]

This is an example of the problem I always have when I'm trying to write about nuclear astrophysics. The topic is dear to me, and when I'm writing, I think to myself "This deserves mentioning, and that too, and that definitely does deserve being mentioned", and don't know what's not as important to include it; everything seems important. I understand that this is not how a difficult topic should be introduced to someone who doesn't know anything about it, and the fact I usually end up with a messy piece of writing whenever I want to be concise when writing about nuclear astrophysics is the reason why I want to practice sharing my ideas in the matter. Just that I know a lot about it doesn't make me good at explaining it.

The main idea I had when I started writing was to explain what it means that the Sun is a G2 class star. Class G is fascinating because it's the last class in which stars will not go supernova. Stars that belong to classes G, K, and M are too small for that, G class stars, like our sun, being the biggest of them. The statement that the Sun is the biggest of the smallest was meant to draw reader's attention because it has two antonymous superlatives.

The part about the CNO cycle was meant to explain what would happen if the Sun were a tad bigger, what it would mean to become an F class star, and how exactly the CNO cycle relates to supernovae.

If the article feels like a collection of loosely related paragraphs that have been stitched together, it's because they kind of are. I started with a much longer, way too long piece of writing, and gradually reduced it to this, five-hundred-something-word piece.

I'll try to apply your comments and rewrite it, but could I ask for help with deciding which parts are key, and which are unnecessary noise that doesn't contribute to reader's ability to understand the topic? I can't do that; everything seems important to me.

 

[jutfrank]

This is an example of the problem I always have when I'm trying to write about nuclear astrophysics. The topic is dear to me, and when I'm writing, I think to myself "This deserves mentioning, and that too, and that definitely does deserve being mentioned", and don't know what's not as important to include it; everything seems important. I understand that this is not how a difficult topic should be introduced to someone who doesn't know anything about it, and the fact I usually end up with a messy piece of writing whenever I want to be concise when writing about nuclear astrophysics is the reason why I want to practice sharing my ideas in the matter. Just that I know a lot about it doesn't make me good at explaining it.

Absolutely. This really underlines the importance of clearly identifying the reader right at the beginning of the planning stage.

I'll try to apply your comments and rewrite it, but could I ask for help with deciding which parts are key, and which are unnecessary noise that doesn't contribute to reader's ability to understand the topic? I can't do that; everything seems important to me.

Like I said, think about the reader first. Imagine me as the reader—someone who is interested in physics and astronomy but who does not have any specialist knowledge, i.e., not a physics student.

The next question to ask is what your aim is. Do you want to teach me something about physics? Or do you want to inspire me to get into physics? Do you want to blow my mind? Or do you want to give me something enjoyable to read while I wait for my dentist appointment? One of the issues you have here as I see it is that this text feels like you're trying to explain physical processes. I don't really want that, as a reader. I see the title and think to myself 'Hey, that's interesting. Biggest of the smallest? What does that mean?' So grab my interest and go with it. Focus on the parts that relate to this idea of being the biggest of the smallest, and make sure you keep coming back to it.

And make sure you plan each paragraph much more thoroughly. Remember to use clear topic sentences. When you've reorganised the ideas, it'll be easy to see which sentences need to be removed.

 

[Glizdka]

Do you want to teach me something about physics? Or do you want to inspire me to get into physics? Do you want to blow my mind? Or do you want to give me something enjoyable to read while I wait for my dentist appointment?

I think the problem is that I want to achieve all of these things at once. Let me limit myself to just inspiring you, the reader, to do your own research, or at the very least give you something enjoyable to read. I'll get rid of all the bits that are unnecessary for this purpose, and base the narration around one main idea, as you've suggested.

Is this better?

---

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. 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. 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.

Let's start with what it means to be a small star. The stars in this group vary in mass widely. 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. 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 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, become what we call red giants.

The Sun will get there; its diameter will increase so much it will engulf the Earth. 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.

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.

The biggest of the biggest are truly scary. 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.

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. The Sun, the biggest of the smallest stars, is safe to live around... for now.

 

[jutfrank]

That's a lot better. Very good.

 

[Glizdka]

That's a lot better. Very good.

Could you help me improve it to excellent?

 

[jutfrank]

Let me ask you how you think it could be improved.

Sometimes a writer needs to get some distance between himself and the text. When he comes back to it later, he sees issues he didn't see before, with different eyes. Part of the skill of writing is imagining that one is the reader.

 

[Glizdka]

Let me ask you how you think it could be improved.

More information, fewer words, less repetition.

Sometimes a writer needs to get some distance between himself and the text. When he comes back to it later, he sees issues he didn't see before, with different eyes. Part of the skill of writing is imagining that one is the reader.

I generally keep track of everything I write to come back to it later when I've already forgotten what it's about, but it takes time, sometimes years. I've made a habit of returning to things I wrote, that includes my essays from when I was still in primary school. It's fascinating to see how your own opinions and ways of expressing them change over time. I think this practice has already improved my writing, but it's slow progress.

How do I make it faster? How can I practice this skill?

---

Would you be interested in investing a few moments of your free time into highlighting a few things in that text and adding a few interspersed comments? I could use some insight that would help me judge what the reader thinks better.

 

[Tarheel]

It's a fascinating subject. Well done!

There are only a couple of errors. That superbright star with a short life is a supernova. (There have been some famous ones throughout history. You probably know them.)

Also try:

Each element is more stable than the previous one

And:

a fate our star will not share


Good night!

 

[jutfrank]

Here you go:

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!

 

[Glizdka]

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?

 

[Glizdka]

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.

 

[jutfrank]

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!

 

[Glizdka]

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.

 

[jutfrank]

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.

 

[Glizdka]

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.

 

[Tarheel]

Try:

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

:up:

 

[Tarheel]

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. ;-) )

 

[emsr2d2]

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 ...".