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).
nitrogen 1356 days ago [-]
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?
mjrpes 1356 days ago [-]
That Fermi's lab link says all the neutrinos produced by the sun are of the same type, electron neutrinos.
tomlu 1356 days ago [-]
Parent comment possibly meant "10^25 neutrinos with an energy level indicating they were produced by the CNO process".
nitrogen 1356 days ago [-]
After reading the article it seems they were referring to total neutrinos, so I think the OP's correction stands.
BurningFrog 1356 days ago [-]
Maybe it's the number passing through Earth?
kurthr 1356 days ago [-]
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.
BurningFrog 1355 days ago [-]
Well, I tried :)
Thanks for the math I was too lazy to do!
mensetmanusman 1356 days ago [-]
“it’s just 13 orders of magnitude”
What’s that between friends?
raxxorrax 1356 days ago [-]
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?
haiguise 1356 days ago [-]
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.
haiguise 1356 days ago [-]
Yup, the more massive a star the short it lives. The Sun for example will live around 10 billion years, whereas a star 10 times the mass of the Sun will only live for 30 or so million years.
Using some hand-wavy arguments you could say that fusion pauses a star's collapse, so the more massive a star is, the more energy generation it needs to stay in equilibrium during this pause.
mnw21cam 1356 days ago [-]
There's a negative feedback loop there. That is, a star of a certain mass needs a certain amount of energy production in order to keep it from collapsing, and that amount of energy production is automatically achieved, because if it were too low then the star would collapse a bit, and increase it.
Therefore, the rate of energy production isn't a consequence of the temperature. The rate of energy production is regulated, so effectively the temperature is a consequence of the required energy production instead.
xattt 1356 days ago [-]
Would this be one hypothesis for the solar sunspot cycle?
bananabreakfast 1356 days ago [-]
No, the balance of gravity to outward radiation pressure from the core is static in nearly all stars that aren't some of the largest we have observed.
The solar sunspot cycle is caused by the periodic inversion of the polarity of the sun's magnetic field.
raxxorrax 1356 days ago [-]
Ah, so it is basically even worse for their lifetime. Thank you for the answer.
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?
davidcuddeback 1356 days ago [-]
No. Size is the dominant factor. Lifespan and what stages of fusion it undergoes are dependent on its size. The more massive the star, the shorter its life span. Red dwarf stars can live for trillions of years, but massive stars may live less than a billion years.
Notice that haiguise wrote "at the core temperature of the Sun." A more massive star has a higher core temperature, and thus haiguise's sentence about fusion rates would no longer apply. Fusion rates are faster at higher temperatures, and that's why more massive stars burn out faster. Notice haiguise wrote "T^4" and "T^20." Our sun is roughly 5000K. Massive stars can exceed 10000K. At twice the temperature, T^4 and T^20 imply 16x and 1,048,576x fusion rates, respectively.
But what is the effect on lifetime of not having any CNO present? If a present-day massive star would have a lifetime of 10 million years, how long would it live if it was a population III star with no CNO?
skykooler 1356 days ago [-]
Carbon is formed in small amounts by normal stellar fusion, and since it is a catalytic process the carbon is conserved. So even an early star would probably have some fusion happening via the CNO cycle.
davidcuddeback 1356 days ago [-]
I'm not sure. I think a lack of metals makes a star less stable and burn out more quickly, but I could be wrong on that. There's some episodes of Astronomy Cast and Ask a Spaceman that I think would answer your question about pop3 stars more reliably than I could.
rymohr 1356 days ago [-]
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?
Robotbeat 1356 days ago [-]
Both fission and fusion release net energy by having products with greater binding energy. The greatest binding energy is iron (and some surrounding elements). Once you get there, no more energy can be released by fusion (or fission).
So it’s not a perpetual motion machine. Iron is the bottom.
(Heavier stuff than iron can be created by fusion, but that absorbs energy instead of releasing it. Supernova create these heavier-than-iron elements like Uranium and gold endothermically... they’re also created by the decaying guts of neutron stars—which are essentially ginormous atomic nuclei held together by gravity instead of nuclear forces—when they collide and some of their guts are released into space.)
chasil 1356 days ago [-]
The S-Process creates elements with atomic numbers higher than Iron, and it does not rely on supernovas or neutron star dissolution.
I'm not sure if endothermic is the best word. IANAP. It seems to usually be used when discussing fusion-based neutron generation. But AFAICT neutron generation, especially as it relates to the s-process, is still largely a thermal process--the greater the temperature, the more neutrons are generated, the faster the s-process evolves. (If you go back to the beginning of the universe all nuclear synthesis represents an endothermic process, right? Though, maybe such semantic games aren't particularly helpful when distinguishing nuclear synthesis processes.)
pletnes 1355 days ago [-]
Nickel-62 is the most stable isotope, if memory serves. It’s not efficiently generated in star fusion, however, so iron-56 is believed by many to be the most stable.
FiatLuxDave 1356 days ago [-]
The term you are looking for is "nuclear binding energy curve". Basically lighter isotopes can gain energy by fusing, and heavier isotopes can gain energy by splitting, but somewhere in the middle (around iron and nickle) the isotopes are the most stable. So you gain energy by moving towards iron, whether from the light end or the heavy end of the periodic table.
7thaccount 1356 days ago [-]
Thermodynamics has some laws (First or Second, I can't remember) that point out perpetual energy or motion machines are impossible.
jahabrewer 1356 days ago [-]
I really don't know, but aren't there some caveats about those assuming that space is flat or something about the rate of expansion?
jschwartzi 1356 days ago [-]
Nope. The three laws are unequivocal. The universe can only increase or maintain entropy through physical processes. It can never return to a lower-entropy state. The laws say nothing about the topography of the universe and it wouldn’t matter anyway.
LeegleechN 1356 days ago [-]
When you dig into it more you realize the second law of thermodynamics is more of a statistical statement and doesn't have the same status as say the laws of quantum mechanics or relativity.
It's possible to create hypothetical situations where all of the must fundamental laws are being followed but the second law of thermodynamics is violated (for example if there are many more 'ordered' states than 'disordered' ones). And there is some vanishingly small chance that it will be violated in our universe for a macroscopically observable length of time.
In practice you won't go wrong by treating it as absolute.
mensetmanusman 1356 days ago [-]
Actually, there is debate about the conservation of energy over cosmological length scales.
e.g. if new voxels of spacetime are created during, and they contain zero-point energy... may account for photons losing energy as they red shift over large distances.
jerf 1356 days ago [-]
Yes, at large scales space expansion can sort of make it so energy is not conserved: http://www.preposterousuniverse.com/blog/2010/02/22/energy-i... Depending on how you look at it, anyhow. One way or another you end up with some sort of unintuitive concept being introduced.
bananabreakfast 1356 days ago [-]
Fusion cannot create the potential for fission and radioactive waste cannot be used to build atomic bombs.
I'm afraid you're quite off base here.
1356 days ago [-]
wiz21c 1356 days ago [-]
IANAPhysicist, but the article makes "feel" how cool all of that is. Good read.
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.
ckarmann 1356 days ago [-]
Well, that's the concept of the CrashCourse channel. This video is actually slow-paced compared for example to their World History series.
It's still interesting. After a while you learn to pause the video to let the information sink in.
dmix 1356 days ago [-]
I like it. It's like listening to a podcast at 1.2x, you can always rewind it if you miss something but the general pace works.
jessaustin 1356 days ago [-]
My podcast app setting is up to 1.7 now. Listening to normal speed spoken word audio (e.g. on the radio) seems like a brain injury.
1356 days ago [-]
ncmncm 1356 days ago [-]
I did not spot what fraction of the sun's output is CNO. Is it known?
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?
evanb 1356 days ago [-]
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.
perl4ever 1356 days ago [-]
>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".
... 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?
nwallin 1356 days ago [-]
> > There was no C12 anywhere in the universe until the first stars began dying.
> ... outside of the stellar cores manufacturing it.
Stellar cores do not produce C12 unless they've already started dying. If there is hydrogen in the core, it will fuse that into helium instead of fusing helium into C12. It's not just a question of "it does happen, just super rarely" either- stars will have an inert helium core surrounded by an expanding shell of hydrogen burning for quite some time before the helium is actually able to begin burning. In the case of the Sun, it's expected to enter the red giant phase, where it burns hydrogen around its inert helium core for 1.2 billion years before it begins burning helium into C12.
> 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?
We have a few models of sources of elements heavier than iron. Supernova are the primary source of almost everything from oxygen up to rubidium.
Once a star goes from its red dwarf stage, where it's still burning hydrogen, into its asymptotic giant branch stage, there is a thin, very hot layer around the helium core, with a dense neutron flux. Heavy elements here will absorb stray neutrons and slowly grow up to elements as heavy as lead. This accounts for many of the elements heavier than rubidium.
Unrelated fun fact: for stars between about 0.5 and 2 times the mass of the Sun, nearly all of the helium burning happens all at once, in the space of a few minutes. For those brief moments, most of the energy generation in that star's galaxy is happening in that star; that star is more powerful than all the other energy sources in its galaxy combined. This is called helium flash. Surprisingly, this doesn't explode the star, all that energy is absorbed by the outer layers. Stars heavier than 2 times the mass of the Sun do not undergo helium flash, as they are heavy and massive enough to begin burning helium earlier and in a non-runaway fashion.
ncmncm 1355 days ago [-]
No much new to me!
Hmm, the Chinese say that helium flash also produces a great deal of lithium.
This article has helped me understand this XKCD comic -https://xkcd.com/2340/ which I was too lazy to look up.
sjcsjc 1356 days ago [-]
Your comment made me read the article. Thanks.
spuz 1356 days ago [-]
How do we distinguish CNO neutrinos from those produced by proton-proton fusion?
QuesnayJr 1356 days ago [-]
According to the article, they have a different amount of energy.
steffenfrost 1356 days ago [-]
Why is the metallicity of the sun so low when they are so high for the planets?
kadoban 1356 days ago [-]
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
ncmncm 1356 days ago [-]
Which planets? The big ones are mostly H2. The small fry with weak gravity lose theirs.
steffenfrost 1355 days ago [-]
There is new data from the Juno Mission, that Jupiter has a diluted core.
"...heavy elements (elements other than hydrogen and helium) are distributed within a region extending to nearly half of Jupiter’s radius."
I'd point out that OP posted a link to a science fiction site
yongjik 1356 days ago [-]
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.
(obviously in conflict with what you posted, and I haven't run through the numbers. Also, our knowledge of radiation effects on organisms is honestly quite limited).
hinkley 1356 days ago [-]
I don't recall if this happened or not but it feels like a Star Trek plotline for them to be near a star when it explodes, have some drama about keeping the shields up and then at the end of the day everyone goes home safely.
But the TLDR here is that the radiation flux from only the neutrinos is enough to kill at 1 astronomical unit from an exploding supernova. Maybe whatever ridiculous process that lets them block phasers but is transparent to visible light and sensor arrays also blocks neutrinos.
The problem with scifi is that each person has a certain proportion of bullshit they are willing to ignore, and at some point it's just too much.
krapp 1356 days ago [-]
>The problem with scifi is that each person has a certain proportion of bullshit they are willing to ignore, and at some point it's just too much.
Nobody watches Star Trek for the science. Which is ironic given that it's apparently inspired a lot of scientists.
rbanffy 1356 days ago [-]
I love Star Trek, but I personally find the engineering practices of the Federation appalling. And, of course, the technobabble is an annoying and lazy subterfuge to avoid proper research when writing a script.
dmarinus 1356 days ago [-]
Ahh too bad we don't have to go to Thalassa then (Songs of distant earth, Arthur C Clarke)
Rendered at 13:50:20 GMT+0000 (Coordinated Universal Time) with Vercel.
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.
Thanks for the math I was too lazy to do!
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.
Using some hand-wavy arguments you could say that fusion pauses a star's collapse, so the more massive a star is, the more energy generation it needs to stay in equilibrium during this pause.
Therefore, the rate of energy production isn't a consequence of the temperature. The rate of energy production is regulated, so effectively the temperature is a consequence of the required energy production instead.
The solar sunspot cycle is caused by the periodic inversion of the polarity of the sun's magnetic field.
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?
Notice that haiguise wrote "at the core temperature of the Sun." A more massive star has a higher core temperature, and thus haiguise's sentence about fusion rates would no longer apply. Fusion rates are faster at higher temperatures, and that's why more massive stars burn out faster. Notice haiguise wrote "T^4" and "T^20." Our sun is roughly 5000K. Massive stars can exceed 10000K. At twice the temperature, T^4 and T^20 imply 16x and 1,048,576x fusion rates, respectively.
Edited to add: Wikipedia has an HR diagram with labels showing lifespans for stars at different temperatures: https://commons.wikimedia.org/wiki/File:Hertzsprung-Russel_S....
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?
See this graph: https://opentextbc.ca/universityphysicsv3openstax/wp-content...
So it’s not a perpetual motion machine. Iron is the bottom.
(Heavier stuff than iron can be created by fusion, but that absorbs energy instead of releasing it. Supernova create these heavier-than-iron elements like Uranium and gold endothermically... they’re also created by the decaying guts of neutron stars—which are essentially ginormous atomic nuclei held together by gravity instead of nuclear forces—when they collide and some of their guts are released into space.)
https://en.wikipedia.org/wiki/S-process
I'm not sure if endothermic is the best word. IANAP. It seems to usually be used when discussing fusion-based neutron generation. But AFAICT neutron generation, especially as it relates to the s-process, is still largely a thermal process--the greater the temperature, the more neutrons are generated, the faster the s-process evolves. (If you go back to the beginning of the universe all nuclear synthesis represents an endothermic process, right? Though, maybe such semantic games aren't particularly helpful when distinguishing nuclear synthesis processes.)
It's possible to create hypothetical situations where all of the must fundamental laws are being followed but the second law of thermodynamics is violated (for example if there are many more 'ordered' states than 'disordered' ones). And there is some vanishingly small chance that it will be violated in our universe for a macroscopically observable length of time.
In practice you won't go wrong by treating it as absolute.
e.g. if new voxels of spacetime are created during, and they contain zero-point energy... may account for photons losing energy as they red shift over large distances.
I'm afraid you're quite off base here.
It's still interesting. After a while you learn to pause the video to let the information sink in.
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?
> ... outside of the stellar cores manufacturing it.
Stellar cores do not produce C12 unless they've already started dying. If there is hydrogen in the core, it will fuse that into helium instead of fusing helium into C12. It's not just a question of "it does happen, just super rarely" either- stars will have an inert helium core surrounded by an expanding shell of hydrogen burning for quite some time before the helium is actually able to begin burning. In the case of the Sun, it's expected to enter the red giant phase, where it burns hydrogen around its inert helium core for 1.2 billion years before it begins burning helium into C12.
> 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?
We have a few models of sources of elements heavier than iron. Supernova are the primary source of almost everything from oxygen up to rubidium.
Once a star goes from its red dwarf stage, where it's still burning hydrogen, into its asymptotic giant branch stage, there is a thin, very hot layer around the helium core, with a dense neutron flux. Heavy elements here will absorb stray neutrons and slowly grow up to elements as heavy as lead. This accounts for many of the elements heavier than rubidium.
The rest of the elements heavier than rubidium are the result of merging neutron stars. See here for more info: https://en.wikipedia.org/wiki/Stellar_nucleosynthesis#Key_re...
Unrelated fun fact: for stars between about 0.5 and 2 times the mass of the Sun, nearly all of the helium burning happens all at once, in the space of a few minutes. For those brief moments, most of the energy generation in that star's galaxy is happening in that star; that star is more powerful than all the other energy sources in its galaxy combined. This is called helium flash. Surprisingly, this doesn't explode the star, all that energy is absorbed by the outer layers. Stars heavier than 2 times the mass of the Sun do not undergo helium flash, as they are heavy and massive enough to begin burning helium earlier and in a non-runaway fashion.
Hmm, the Chinese say that helium flash also produces a great deal of lithium.
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
(obviously in conflict with what you posted, and I haven't run through the numbers. Also, our knowledge of radiation effects on organisms is honestly quite limited).
But the TLDR here is that the radiation flux from only the neutrinos is enough to kill at 1 astronomical unit from an exploding supernova. Maybe whatever ridiculous process that lets them block phasers but is transparent to visible light and sensor arrays also blocks neutrinos.
The problem with scifi is that each person has a certain proportion of bullshit they are willing to ignore, and at some point it's just too much.
Nobody watches Star Trek for the science. Which is ironic given that it's apparently inspired a lot of scientists.