The article mentions that the sun produces 10^25 neutrinos every second. This felt quite off.
I found an Ohio State PDF that mentioned 2 * 10^38 neutrinos per second. Elsewhere I saw mentioned 7 * 10^10 particles going through your thumb every second (1 cm^2). Times that by cm^2 surface area of sphere that is radius of distance between sun and earth (3 * 10^27), and the 10^38 looks like the correct one.
Interestingly, I also saw mentioned a nuclear reactor makes 10^20 neutrinos per second.
EDIT: Not sure why the downvote. Because I didn't link sources?
Sorry... not many great sources here but everything points to the 10^38 number. The 10^25 stated in the article may be mistakenly using the very similar number for joules of energy created each second by the sun (10^25).
Unfortunately, it would only get you down ~10^-8, which is still 5 orders of magnitude off (38-8=30>25).
Earth is ~12,700km diameter while the Sun is ~690,000km or a ratio of ~50x. The Sun appears as ~0.5deg from here so the Earth should be ~0.01deg from there.
A steradian is ~3300deg^2 so we're looking at ~3*10^-8 steradians subtended by earth and roughly that fraction of total neutrinos. Closer, but no cigar.
Someone once told me that CNO fusion doesn't happen in our star because it is too small. I think he would be happy to be proven wrong.
If the CNO process is allegedly more efficient, does that mean a star with a higher mass might live longer than a smaller one that mainly use proton-proton fusion? Or is it even worse for the lifetime of a star?
CNO fusion does happen but at a fraction of the rate of pp fusion at the core temperature of the Sun. CNO fusion is more efficient in the sense that it is much more strongly temperature dependent. For pp fusion, the rate goes with T^4, but for CNO it is T^20.
Does that mean hydrogen would be used up much more quickly in high temperature stars? If I remember correctly, that's why large stars have shorter lifespans.
You seem to know a lot about this stuff. I have a question for you.
If fusion creates the potential for fission (radioactive waste) and radioactive waste can be used to build atomic bombs, how have we not figured out how to make mini perpetual-energy reactors?
Wow, I'm exhausted for this guy. The way this is edited is just bad. The guy needs to take a breath. They started the audio from the next edit before the guy has fully completed his current sentence. It's like they had a hard constraint on how long the video could be, and cut out all of the silence to make it fit.
You might expect two alphas to make 8Be and then another alpha to make 12C, but 8Be is unstable on a very short timescale 10^-16 seconds.
Amazingly, 12C has a resonance called the Hoyle State that allows a triple alpha to 12C process. The Hoyle State is basically the only quantitative PREdiction of the anthropic principle.
Roughly 1% of the Sun's output is from the CNO cycle.
The original C12 came from the triple alpha process. Three helium atoms collide to form C12 more-or-less directly. Technically, two helium atoms combine to form Be8, which combines with a third helium atom to form C12, but the half-life of Be8 is 8e-17 seconds.
There was no C12 anywhere in the universe until the first stars began dying. Only after the first generation of stars lived their entire lives, and off-gassed C12 (and other heavy elements) and the next generation of stars formed from the remnants did any stars exist with C12 in them, or planetary disks form around them that contained any elements heavier than lithium.
This had fairly significant effects. First of all, the first generation of stars (called Population III stars) could not burn hydrogen via the CNO cycle, which can happen much more rapidly than the proton proton chain. Second, they were much more transparent. Combined, this means that they were much, much less constrained in terms of mass than contemporary stars. They could have been enormous. They could have been large enough that it was energetic enough in their cores that the highest energy gamma rays might preferentially form positron-electron pairs- that was a lower energy state than just being plain old light. This would reduce the temperature in the core, which would cause it to contract. As it contracted, it would heat up again- which would cause more electron position pair production.
Normally, fusion in the core of a star is self regulating. As it heats up, it expands, which reduces the rate of fusion. This causes it to cool down, which causes it to shrink. This increases the rate of production. This process stable and self regulating.
However, pair-production throws a wrench in all this. Higher temperatures are short circuited into pair-production, which causes it to shrink, which increases the rate of fusion, which increased the rate of pair production, which causes it to shrink more. It's a feedback loop that creates a very small, very very very hot core. And the core collapses. But this doesn't collapse into a black hole or anything, it shrinks until the point where the density of positrons is so great that they annihilate as fast as they are being created. At this point, the feedback loop breaks, and the entire star explodes in an impossibly powerful supernova. There's no warning and no remnant; it's a normal (albeit very large and very bright) star one moment, a ridiculous supernova the next, and nothing but an expanding gas cloud containing a wide variety of heavy elements the next.
We have never observed a Population III star, or a pair-production supernova. Just hypothesized about them. It's odd that we've never seen a population III star- why isn't there a small red dwarf kicking around (which can easily have a lifetime of a trillion years) with no elements heavier than helium in it? (lithium is destroyed fairly quickly in a star) We think that this tells us something about star formation; there basically had to have been no small stars in the early universe, just very large ones. It's an open question as to why.
You might imagine a planet with life on it who are quite annoyed by this. They're minding their own business, when suddenly their star explodes and they're all dead. But this couldn't have happened. Remember there's no elements heavier than lithium at this point, and only a minuscule quantity of lithium at that. There wasn't enough "stuff" in the star's disk to form planets, and if a small chunk of lithium/lithium hydride managed to coalesce into a planetoid like object, there's not really any chemistry interesting enough to form life that can happen.
... outside of the stellar cores manufacturing it.
Fascinating, I had never encountered this. Stellar core all electron-positron pairs, momentarily.
So we get all the elements heavier than iron from these insane-o-novas and from ordinary supernovas, often by decay from even heavier isotopes. Do we know how much of each is from which? E.g., did all the platinum or something start from pop iii output?
I think because H2 is so common. Given that and how gravity works, let's look at the possibilities:
small thing (say up to size of smaller planets): only solids can clump together and stay together, gas would just fizz away
medium thing (earthish to gas giantish, say): solids clump together and that provides enough gravity (and sometimes magnetics) to capture/keep some gas too
large thing (star sized): you can just capture everything around. Sure that'll contain some metal, but since most of what's out there is H2 and you're gulping it all up, you end up mostly gas
Phil Plait's Bad Astronomy is a legit science blog (man, the term feels so quaint in 2020...) - even though it is hosted in a shady-looking syfy.com website.
Readit News
I found an Ohio State PDF that mentioned 2 * 10^38 neutrinos per second. Elsewhere I saw mentioned 7 * 10^10 particles going through your thumb every second (1 cm^2). Times that by cm^2 surface area of sphere that is radius of distance between sun and earth (3 * 10^27), and the 10^38 looks like the correct one.
Interestingly, I also saw mentioned a nuclear reactor makes 10^20 neutrinos per second.
EDIT: Not sure why the downvote. Because I didn't link sources?
Here's the powerpoint presentation: http://www.physics.ohio-state.edu/~hughes/freshman_seminar/p...
Here is Fermi lab saying number per second in thumbnail: https://neutrinos.fnal.gov/sources/solar-neutrinos/
Here's someone's homework that gives the calculation total neutrinos per second based on number of He fusion reactions, which also matches 10^38. http://www.as.utexas.edu/astronomy/education/fall08/lacy/sec...
Sorry... not many great sources here but everything points to the 10^38 number. The 10^25 stated in the article may be mistakenly using the very similar number for joules of energy created each second by the sun (10^25).
Could they also be using a number for a specific type of neutrino?
Earth is ~12,700km diameter while the Sun is ~690,000km or a ratio of ~50x. The Sun appears as ~0.5deg from here so the Earth should be ~0.01deg from there.
A steradian is ~3300deg^2 so we're looking at ~3*10^-8 steradians subtended by earth and roughly that fraction of total neutrinos. Closer, but no cigar.
What’s that between friends?
If the CNO process is allegedly more efficient, does that mean a star with a higher mass might live longer than a smaller one that mainly use proton-proton fusion? Or is it even worse for the lifetime of a star?
See eg. https://websites.pmc.ucsc.edu/~glatz/astr_112/lectures/notes... for a more detailed explanation.
Would that mean that massive first generation stars could live longer than their current brethren, since there wasn't any C, N, or O yet?
If fusion creates the potential for fission (radioactive waste) and radioactive waste can be used to build atomic bombs, how have we not figured out how to make mini perpetual-energy reactors?
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Also, what process makes the original C-12? Assuming very little of it started out there. Or does the primordial C, N, and O just circulate?
Amazingly, 12C has a resonance called the Hoyle State that allows a triple alpha to 12C process. The Hoyle State is basically the only quantitative PREdiction of the anthropic principle.
https://en.wikipedia.org/wiki/Carbon-12
The original C12 came from the triple alpha process. Three helium atoms collide to form C12 more-or-less directly. Technically, two helium atoms combine to form Be8, which combines with a third helium atom to form C12, but the half-life of Be8 is 8e-17 seconds.
There was no C12 anywhere in the universe until the first stars began dying. Only after the first generation of stars lived their entire lives, and off-gassed C12 (and other heavy elements) and the next generation of stars formed from the remnants did any stars exist with C12 in them, or planetary disks form around them that contained any elements heavier than lithium.
This had fairly significant effects. First of all, the first generation of stars (called Population III stars) could not burn hydrogen via the CNO cycle, which can happen much more rapidly than the proton proton chain. Second, they were much more transparent. Combined, this means that they were much, much less constrained in terms of mass than contemporary stars. They could have been enormous. They could have been large enough that it was energetic enough in their cores that the highest energy gamma rays might preferentially form positron-electron pairs- that was a lower energy state than just being plain old light. This would reduce the temperature in the core, which would cause it to contract. As it contracted, it would heat up again- which would cause more electron position pair production.
Normally, fusion in the core of a star is self regulating. As it heats up, it expands, which reduces the rate of fusion. This causes it to cool down, which causes it to shrink. This increases the rate of production. This process stable and self regulating.
However, pair-production throws a wrench in all this. Higher temperatures are short circuited into pair-production, which causes it to shrink, which increases the rate of fusion, which increased the rate of pair production, which causes it to shrink more. It's a feedback loop that creates a very small, very very very hot core. And the core collapses. But this doesn't collapse into a black hole or anything, it shrinks until the point where the density of positrons is so great that they annihilate as fast as they are being created. At this point, the feedback loop breaks, and the entire star explodes in an impossibly powerful supernova. There's no warning and no remnant; it's a normal (albeit very large and very bright) star one moment, a ridiculous supernova the next, and nothing but an expanding gas cloud containing a wide variety of heavy elements the next.
We have never observed a Population III star, or a pair-production supernova. Just hypothesized about them. It's odd that we've never seen a population III star- why isn't there a small red dwarf kicking around (which can easily have a lifetime of a trillion years) with no elements heavier than helium in it? (lithium is destroyed fairly quickly in a star) We think that this tells us something about star formation; there basically had to have been no small stars in the early universe, just very large ones. It's an open question as to why.
You might imagine a planet with life on it who are quite annoyed by this. They're minding their own business, when suddenly their star explodes and they're all dead. But this couldn't have happened. Remember there's no elements heavier than lithium at this point, and only a minuscule quantity of lithium at that. There wasn't enough "stuff" in the star's disk to form planets, and if a small chunk of lithium/lithium hydride managed to coalesce into a planetoid like object, there's not really any chemistry interesting enough to form life that can happen.
It's interesting to think about what could have happened when the whole universe initially cooled to "room temperature".
https://www.nature.com/news/life-possible-in-the-early-unive...
https://www.cfa.harvard.edu/~loeb/habitable.pdf
... outside of the stellar cores manufacturing it.
Fascinating, I had never encountered this. Stellar core all electron-positron pairs, momentarily.
So we get all the elements heavier than iron from these insane-o-novas and from ordinary supernovas, often by decay from even heavier isotopes. Do we know how much of each is from which? E.g., did all the platinum or something start from pop iii output?
small thing (say up to size of smaller planets): only solids can clump together and stay together, gas would just fizz away
medium thing (earthish to gas giantish, say): solids clump together and that provides enough gravity (and sometimes magnetics) to capture/keep some gas too
large thing (star sized): you can just capture everything around. Sure that'll contain some metal, but since most of what's out there is H2 and you're gulping it all up, you end up mostly gas
"...heavy elements (elements other than hydrogen and helium) are distributed within a region extending to nearly half of Jupiter’s radius."
https://www.nature.com/articles/s41586-019-1470-2