
CNO neutrinos from the Sun are finally detected - rbanffy
https://www.syfy.com/syfywire/after-nearly-a-century-elusive-cno-neutrinos-are-finally-seen-from-the-sun
======
mjrpes
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?

Here's the powerpoint presentation: [http://www.physics.ohio-
state.edu/~hughes/freshman_seminar/p...](http://www.physics.ohio-
state.edu/~hughes/freshman_seminar/press/minos_new#:~:text=From%20the%20process%20of%20thermonuclear,2x1038%20per%20second%20total.&text=A%20standard%20nuclear%20power%20plant,energy%20is%20around%204%20MeV)

Here is Fermi lab saying number per second in thumbnail:
[https://neutrinos.fnal.gov/sources/solar-
neutrinos/](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...](http://www.as.utexas.edu/astronomy/education/fall08/lacy/secure/hw5.pdf)

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
_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
That Fermi's lab link says all the neutrinos produced by the sun are of the
same type, electron neutrinos.

~~~
tomlu
Parent comment possibly meant "10^25 neutrinos with an energy level indicating
they were produced by the CNO process".

~~~
nitrogen
After reading the article it seems they were referring to total neutrinos, so
I think the OP's correction stands.

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raxxorrax
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
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.

See eg.
[https://websites.pmc.ucsc.edu/~glatz/astr_112/lectures/notes...](https://websites.pmc.ucsc.edu/~glatz/astr_112/lectures/notes8.pdf)
for a more detailed explanation.

~~~
rymohr
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
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).

See this graph: [https://opentextbc.ca/universityphysicsv3openstax/wp-
content...](https://opentextbc.ca/universityphysicsv3openstax/wp-
content/uploads/sites/273/2019/07/CNX_UPhysics_43_02_BindingEng-1.jpg)

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
The S-Process creates elements with atomic numbers higher than Iron, and it
does not rely on supernovas or neutron star dissolution.

[https://en.wikipedia.org/wiki/S-process](https://en.wikipedia.org/wiki/S-process)

~~~
wahern
S-process is still endothermic, though, right?

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.)

------
wiz21c
IANAPhysicist, but the article makes "feel" how cool all of that is. Good
read.

~~~
urxvtcd
The author has a series on youtube where he explains the basics of astronomy
in a very passionate manner. First episode here:
[https://www.youtube.com/watch?v=0rHUDWjR5gg](https://www.youtube.com/watch?v=0rHUDWjR5gg)

~~~
dylan604
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.

~~~
dmix
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
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.

------
ncmncm
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?

~~~
nwallin
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.

~~~
ncmncm
> " _There was no C12 anywhere in the universe..._ "

... 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
> > 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.

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...](https://en.wikipedia.org/wiki/Stellar_nucleosynthesis#Key_reactions)

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
No much new to me!

Hmm, the Chinese say that helium flash also produces a great deal of lithium.

~~~
ncmncm
*So much.

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MarcScott
This article has helped me understand this XKCD comic
-[https://xkcd.com/2340/](https://xkcd.com/2340/) which I was too lazy to look
up.

~~~
sjcsjc
Your comment made me read the article. Thanks.

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spuz
How do we distinguish CNO neutrinos from those produced by proton-proton
fusion?

~~~
QuesnayJr
According to the article, they have a different amount of energy.

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steffenfrost
Why is the metallicity of the sun so low when they are so high for the
planets?

~~~
ncmncm
Which planets? The big ones are mostly H2. The small fry with weak gravity
lose theirs.

~~~
steffenfrost
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."

[https://www.nature.com/articles/s41586-019-1470-2](https://www.nature.com/articles/s41586-019-1470-2)

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dangoljames
I'd point out that OP posted a link to a science fiction site

~~~
yongjik
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.

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dmix
The linked XKCD article on "Lethal Neutrinos" is great [https://what-
if.xkcd.com/73/](https://what-if.xkcd.com/73/)

~~~
hinkley
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
>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
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
Ahh too bad we don't have to go to Thalassa then (Songs of distant earth,
Arthur C Clarke)

