Submitted by PHealthy t3_124xb33 in askscience
Paaaaap t1_je1bq4r wrote
So the most common element is hydrogen, followed by helium and so on. Stars are basically fusion reactors that fuse element up untill iron on the periodic table. The Wikipedia page of " Abundance of the chemical elements " will show you how little of the universe is not hydrogen helium. So by mass I'd say it's quite rare for sure, but compared to things like gold or uranium it's far less rare. Most we can do are estimates since it's really hard to find direct evidence on far away planets.
AuDHDiego t1_je1e484 wrote
IIRC quasars and supernovae are where you get the heavier elements, right?
Mord42 t1_je1h4dp wrote
Yes! The creation of those elements take energy instead of releasing it.
AuDHDiego t1_je1hc6t wrote
Thank you! It's fascinating that we have any kind of nontrivial amounts of those elements at all in our grasp, considering their sources.
Walmsley7 t1_je1j43m wrote
Somebody may correct me if I’m wrong, but it helps that the stars that go supernovae have comparatively short life spans, so there have been several more “generations” of them. If I recall, the life span of those stars is measured in the millions of years, versus our sun which is projected to have a 10 billion total life span (and is about 4.5 billion years into it).
Edit: and versus the estimated ~14 billion year age of the universe.
forte2718 t1_je1pe8m wrote
You're somewhat correct — there are basically two known generations of stars, and a third hypothesized one.
The very first generation of stars would have lasted millions to tens of millions of years, were very metal-poor (being composed almost exclusively of hydrogen and helium left over from the big bang) and would almost all have gone supernova early on. None are still around today, and there is only scant evidence that they existed at all. Obtaining better evidence for this first generation of stars is one of the primary missions of the James Webb Space Telescope.
The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars. These were lower in mass on average and lasted much longer, hundreds of millions to billions of years.
Our Sun is a third generation star, which was likely formed from the compression of gas by second-generation stars going supernova. Third-generation stars like our Sun are much lower mass and higher metallicity, and have much longer lives on average.
All that being said, we would have obtained a mix of many elements because our Sun (and most second- and third-generation stars) and solar system were almost certainly formed out of gas clouds that had materials from numerous other exploded stars from both the current and previous generation. The second generation of stars was a lot more diverse than the first generation, and the third generation even moreso, so the diversity of elements that we seen in our solar system today comes from many different kinds of exploded stars in the two most recent generations.
Hope that helps!
Seicair t1_je2cmmp wrote
> The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars.
I’d like to point out for any chemistry enthusiasts not well versed in astronomy. In astronomy, it’s hydrogen, helium, or metal.
Beer_in_an_esky t1_je2vjad wrote
Astronomy, the field where Oxygen is a metal, and four orders of magnitude can be a rounding error. Love it.
SkoomaDentist t1_je2utiy wrote
Out of curiosity, why this divide? Is it just because hydrogen and helium constitute such large part of all matter that it makes no sense to divide the tiny remaining part further?
D180 t1_je4o60e wrote
That's the most important part I think, hydrogen and helium make up 98% of the universe as they were produced immediately after the big bang, all other elements matter much less.
There's also the fact that the chemical behaviour of an element does not matter much at the temperatures encountered in stars - the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together. If you heat up iron to 3000°C it stops being a metal and just behaves like any other dense, hot gas. But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures (for example, they rise to the surface of a star)
Seicair t1_je691wn wrote
> the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together.[...] But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures
Hey, that makes sense, thanks for the explanation. I've kinda wondered why they use the terminology myself since I learned it. My specialty is organic chemistry.
GnarlyNarwhalNoms t1_je1q363 wrote
Yes, the luminousity of a star (which is a direct consequence of "units of matter fused per second") goes up as greater than the cube of mass, about M^(3.5). That means that even though they contain a lot more fuel, they burn through it far more quickly. So for example, a star with two solar masses has roughly twice as much fuel* as the sun, but it burns around 13 times as fast, so its lifespan is less than one sixth of the sun's, or maybe around 1.5 billion years**
So if you plug in a star with, say, 20 solar masses, all of a sudden, you're looking at a lifespan of a small fraction of a billion years.
* It gets a bit more complicated in that large and medium stars have a radiative zone at the core (high pressure supressing convection) underneath a convective zone at the surface. Small stars, smaller than the sun, are entirely convective, meaning that they can use the fuel from the entire stellar mass. Large stars have smaller convective zones which don't interface with the core, meaning that they can run out of fuel even if there's a substantial amount of hydrogen in the upper layers of the star. This is why using mass to calculate star lifetimes isn't as simple as using the entire star's mass to look at how much fuel will be fused. This is also why red dwarf stars have exceedingly long lifespans.
**These are highly handwavey numbers, don't check me on it, but you get the gist.
polaarbear t1_je1pcmi wrote
This is only true for Type II supernova. Type Ia supernova occur when a white dwarf (created in the death of a star like our sun) siphons enough mass of a companion star.
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starlevel01 t1_je1qdhd wrote
> It's fascinating that we have any kind of nontrivial amounts of those elements at all in our grasp, considering their sources.
It's easier to think of it as an extremely large number (number of stars) multiplied by an extremely small number (probability of producing those elements) which rounds out to a reasonably-sized number.
Aethelric t1_je2lle8 wrote
The takeaway is not that the amounts available are nontrivial; rather, it's that we are trivial.
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PatrickKieliszek t1_je1s5yi wrote
There are actually some exothermic reactions that produce elements more massive than iron.
However, these are usually very short lived in the time immediately before supernovae and are limited by photodisintegration. They don't meaningfully contribute to the amount of heavier elements (Which are primarily produced during nova).
Mord42 t1_je33pck wrote
That's interesting! Thanks for the information.
platoprime t1_je1n9ju wrote
Mergers of neutron stars are the probable primary source of heavier elements according to recent research.
AuDHDiego t1_je1nh67 wrote
This is fascinating, and it's remarkable that we have all that many heavier elements, considering all that
platoprime t1_je1orkq wrote
Yes it is! I absolutely love this stuff.
Estimates put the current count of neutron stars at one billion in our galaxy and a total of one hundred billion stars total. So around one percent of stars in our galaxy are neutron stars. Most stars are in binary orbits so taken all together it lines up with the distribution quite nicely I think. Plus remember it's by mass so one gold atom counts for as much as 79 hydrogen atoms. If we viewed it by atomic count instead of total mass heavy elements are even rarer than the graph implies.
adamginsburg t1_je1v4o8 wrote
Just a quick two cents here: supernovae, yes, but not quasars. Quasars are accreting black holes, and while there might be some production of heavy elements in their accretion disks, those elements likely do not get returned to the surrounding galaxy to form new stars. Besides supernovae, neutron star mergers (which another poster already noted) may also produce significant heavy elements, and AGB stars also produce some of the moderately-heavy elements - but with quite a different distribution. Cartoons like this one https://svs.gsfc.nasa.gov/13873 give a good summary of which routes are responsible for making each.
AuDHDiego t1_je1w58v wrote
This is really helpful thank you! So there's not much significant matter expelled from accretion disks?
adamginsburg t1_je1wwcd wrote
There actually is a decent amount expelled in gigantic jets, but the jets from quasars are relativistic (i.e., travel at a significant fraction of the speed of light) and escape the galaxy. Google "radio galaxies" and look at those images: they show jets shooting to megaparsec size scales (i.e., 10-100x bigger than galaxies), so that material totally escapes the galaxy.
That said, there is probably some material from quasars that gets mixed back into the galaxy - I think not that much, but honestly there's a lot unknown about gas cycling in the vicinity of rapidly accreting black holes. Nevertheless, even if all the accretion disk material got fed back into the galaxy, it would represent a truly tiny fraction of the galaxy's mass, much less than the material made by supernovae (our black hole is 10^6 solar masses, our galaxy is ~10^12 solar masses, of which ~10^11 is baryonic - so the black hole is a tiny fraction of the galaxy, and the accretion disk is a tiny fraction of that. my numbers here are super rough)
AuDHDiego t1_je22f3r wrote
Oh just saw that you're the author of the referenced paper! Gosh oops that I missed that!
​
Congratulations on finding the salty disk!
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Blakut t1_je1d9ih wrote
What matters is how stars fuse them. Iron, nickel, neon, are more common than chlorine.
velociraptorfarmer t1_je1kgzn wrote
Similar to how oxygen is actually the 3rd most common element in the universe.
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PHealthy OP t1_je1q4vf wrote
I was looking for more than just a Google answer, for relative abundance it would seem there are massive deposits where it is found but yes, absolutely, there is very little NaCl in the universe.
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cited t1_je1ow62 wrote
Isn't "it's somewhere between the most common in the universe and the most rare in the universe" not particularly precise?
[deleted] t1_je1kmjq wrote
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Snatch_Pastry t1_je1llzf wrote
We're not even close to depleting earth's supply. It's just that years ago, it stopped being economical to bother capturing it as it comes up with natural gas. Uranium decay creates the helium deep underground. So when it gets expensive enough, they'll rebuild the capture and separation equipment.
[deleted] t1_je1mkbo wrote
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platoprime t1_je1nq84 wrote
The important point doesn't change though. We can tap tons of wells of helium that we didn't tap for natural gas because there was too much helium. The price just has to go up to make that profitable. We're not going to run out of helium any time soon.
javanator999 t1_je1nrmv wrote
Qatar is currently producing about 1/3 of the total helium production from its natural gas production. It could produce more if the price was higher.
Helium in natural gas isn't that rare, it's just that the very low prices we've had for years don't make it economical to extract.
Snatch_Pastry t1_je1og05 wrote
Interesting. He's not shitting about the cost of doing by air separation, though, he may actually be underselling it. I used to work in air separation, and various companies have tried going after the rare gasses, like xenon and helium. You're dealing with so few molecules that keeping the in/out flow in the columns stable is nearly impossible.
Nyrin t1_je1p2vp wrote
The news you hear about helium supply is not (or shouldn't be) about extractable amounts on the planet — it's about what's commercially available.
Extraordinary amounts of helium are just discarded during things like natural gas extraction because helium isn't profitable enough for those companies to extract, store, and sell. That means commercial supply goes down and, with constant or increasing demand, price goes up. At some point, it becomes profitable to separate and sell it again, at which point supply increases, price goes down, and the cycle repeats.
This process is being intensified, especially in creating lower price floors, by long-standing selloffs of nationalized helium reserves that were created when we thought dirigibles were the future of warfare.
Helium is effectively a non-renewable resource (decay products are created very slowly and need to accumulate over millions of years to be harvestable, besides) and we will run out of it someday, but that day is still very far off and unlikely to happen in the lifetime of anyone alive barring major life extension advancements (yes, please!).
What we will see is continued boom/bust cycles as reserves are depleted and markets stabilize on current real extraction costs. And it'll likely be a steady increase over time as the long-term depressive effect of stockpile release dwindles.
Helium can be synthesized via nuclear reactions and, in a hypothetical situation where the Earth really "ran out," that's what we'd likely end up doing. It'd just be many orders of magnitude more expensive than today and probably make asteroid capture look very appealing. But that hypothetical day is very far off past much more prominent existential threats.
fizzmore t1_je1lk1o wrote
Well, it's not a uniform distribution. The fact that it's the second most abundant element in the universe doesn't mean it was the second most abundant element on Earth.
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zarrel40 t1_je37f1y wrote
Interesting!
As an aside, where are the other elements beyond Iron coming from if not stars?
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tidderred t1_je1vi30 wrote
(Have read through the first few chapters of Stars and Their Spectra by James Kaler, so most of what I will say is explained in more detail there.)
On the topic of chemical composition of stars, only cool stars, like M dwarfs or L and T type ultra-cool brown dwarfs can have complex molecules survive in their cores. If the star is any hotter (which is the result of a lot of other variables) only pure elements or hardy molecules with strong bonds can survive that chaotic environment without being ripped apart. For example L-T stars can be identified if their chronosphere contains TiO, which is a) a molecule and b) has titanium, which is heavier than sodium or chloride, so somewhere out there NaCl should exist.
But as far as we know L-T stars along with white dwarves and type 0 stars make up about 5% of stars in the universe, so not a lot of NaCl should exist in stars both in quantity and spatial spread.
Like you said, detecting chemicals on exoplanets is much more challenging, where NaCl can exist in greater quantities, without being disturbed by immense heat and pressure stellar cores have. We just cannot know for sure, but it is fun to think about! (Which is a very non-sciency way of saying we should be looking into this.)
EDIT: After an experienced scientist chimed in I realized my answer didn't take into account the fact that the molecule itself needs to radiate some energy for us to detect it, or it should absorb some energy from the envelope to create noticeable dips in the spectrum. In either case, it will heat up, not so much to break the molecule, but not as cold as L-T stars would require (about a few hundred kelvin at most). I also didn't base my speculation on any real detection, just wanted to chime in since what I learned about seemed to coincide with this topic. Still leaving this up in case anyone wants to take this info and go on their own rabbit hole. Also, just saw JWST detected some silicate dust in a what looks to be a hot jupiter (VHS 1256 b), so exoplanets being challenging to study might already be changing with JWST's observations.
adamginsburg t1_je29j3x wrote
I think you're on the right track that L/T/Y dwarves (brown dwarves) should have cool enough atmospheres to have NaCl in them. I don't know what references to go to say for sure, though.
One of the problems isn't just that the salt molecules need to be warm to emit (that's true), but that the wavelengths at which we see their radiation are tough to observe in stars and planets. The detection we reported was in a disk - which is very, very big compared to a star or planet, and so we could see it at radio/millimeter wavelengths. We generally can only detect stars themselves at optical and infrared wavelengths, and it turns out that NaCl and KCl don't have many transitions at wavelengths we usually observe (e.g., https://ui.adsabs.harvard.edu/abs/2014MNRAS.442.1821B/abstract). Most of their strong emission/absorption lines are at >=26 microns, which is just at the edge of what JWST is capable of observing with its MIRI instrument. No other telescope has observed at these wavelengths with enough sensitivity to pick up salt molecules. I think there's some possibility JWST will detect salts in either hot jupiters or brown dwarves, though; there are weaker salt lines covering JWST's whole range. The trick is, there are lots of other molecules that could obscure the salts in an atmosphere - I'm not sure whether we'll be able to identify the molecules cleanly. It's a much easier job at radio wavelengths.
vintage2019 t1_je4zfaf wrote
Why is iron more common than lighter elements?
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