[HN Gopher] Ancient stars made extraordinarily heavy elements, r...
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Ancient stars made extraordinarily heavy elements, researchers find
Author : wglb
Score : 81 points
Date : 2023-12-08 04:47 UTC (18 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| daveslash wrote:
| I think it's interesting to speculate on how an alien
| civilization might develop technology, and in what order, if they
| were to originate on a planet with different ratios of elements
| than Earth, including access to these super heavy elements.
| ajross wrote:
| There is no reason to suspect any of these elements are stable.
| The paper seems to be alleging that they existed in quantity at
| the end of the r-process such that they produced otherwise hard
| to explain ratios of other stable nucleii (i.e. their fission
| products).
|
| If there were stable transuranic nucleii, we'd need to work
| very hard to explain why we can't find any in the universe.
| thsksbd wrote:
| Well we know how stable many of them are - we've synthesized
| them and out them in our fire alarms
| Cockbrand wrote:
| Andy Weir's novel _Project Hail Mary_ explores this to some
| extent. Well, not super heavy elements, but heavier ones than
| the stuff we're made of.
| philipkglass wrote:
| All of these super heavy elements are radioactive with short
| half lives, so they wouldn't be accessible as ores even on
| planets that formed close to these stars. The article refers to
| elements with atomic weights higher than 260, which would mean
| elements like lawrencium and rutherfordium; they all have half
| lives of less than a day.
|
| I have had a related thought about uranium, though. The fissile
| isotope that's useful for power generation and bombs, uranium
| 235, is only about 0.7% of uranium that's found on Earth. When
| uranium is formed in a supernova, there's actually _more_
| uranium 235 produced than uranium 238; this freshly produced
| uranium is about 62% U-235 [1]. The reason that U-235 is so
| rare on Earth is that U-235 decays faster than U-238 and our
| uranium is billions of years old. But if it 's possible for a
| technological civilization to develop on a planet with much
| fresher uranium content, natural uranium there could contain a
| double-digit percentage of U-235. Under those conditions it
| would be easy to accidentally discover nuclear fission and
| naturally occurring reactors like Oklo [2] would be common.
|
| [1] https://world-nuclear.org/information-library/nuclear-
| fuel-c...
|
| [2] https://www.iaea.org/newscenter/news/meet-oklo-the-earths-
| tw...
| chasil wrote:
| If the Cambrian explosion had happened sooner, then this
| would have been possible.
| cstross wrote:
| The Cambrian explosion was, however, constrained by the
| partial pressure of oxygen in the hydrosphere (and,
| indirectly, the atmosphere). And free O2 couldn't begin to
| build up in seawater until after the Great Oxygen
| Catastrophe when the crust and upper mantle was finally
| fully oxidized, mopping up all the unoxidized iron and
| other elements. (Which in turn killed off almost all
| previous life forms, which were methanogenic and to which
| oxygen was a deadly poison/metabolic waste product.) The
| speed with which this happened was in turn constrained by
| tectonic subduction ... it all turns out to be a knotty
| ball of string that took at least a couple of billion years
| to unwind.
| consp wrote:
| > they all have half lives less than a day.
|
| Isn't it the case it is currently not possible to create any
| neutron heavy isotopes and that causes the half-lives to be
| on the low end?
| philipkglass wrote:
| _Isn 't it the case it is currently not possible to create
| any neutron heavy isotopes and that causes the half-lives
| to be on the low end?_
|
| All of these isotopes are neutron-heavy. Lawrencium 261 has
| 103 protons and 158 neutrons, for example.
|
| In fact, the only stable isotopes with fewer neutrons than
| protons are helium 3 and ordinary hydrogen (protium).
| saalweachter wrote:
| I think he's referring to the way that eg lawrencium has
| a half-life that ~increases with the neutrons in the
| isotopes we've produced, from seconds for Lr-256 to hours
| for Lr-266.
|
| It isn't crazy to postulate, as a layman, that if we
| synthesized Lr-276, say, it might have a longer half-
| life.
|
| (Not that we expect that pattern to continue
| indefinitely, but still, have we discovered the most
| stable isotope of lawrencium yet?)
| chorsestudios wrote:
| From [2] " All natural uranium today contains 0.720% of
| U-235. If you were to extract it from the Earth's crust, or
| from rocks from the moon or in meteorites, that's what you
| would find. But that bit of rock from Oklo contained only
| 0.717%."
|
| I find it interesting that the .003% difference in U-235 was
| a large enough deviation to attract attention to Oklo. Thanks
| for the link
| Beijinger wrote:
| "The article refers to elements with atomic weights higher
| than 260, which would mean elements like lawrencium and
| rutherfordium; they all have half lives of less than a day."
|
| Does the article really mean that? " r-process can produce
| atoms with an atomic mass of at LEAST 260 before they
| fission."
|
| https://en.wikipedia.org/wiki/Island_of_stability
|
| and
|
| https://www.researchgate.net/publication/279166139_Charge_sp.
| ..
| adrian_b wrote:
| According to current knowledge, the r-process can produce
| atoms with an atomic mass of at MOST 260, i.e. mainly up to
| fermium 257.
|
| Moreover, the nuclides with atomic mass close to 260, i.e.
| isotopes of einsteinium and fermium, would be produced in
| relatively small quantities in comparison with lighter
| elements.
|
| Exceeding 260 is highly improbable because such nuclei
| fission spontaneously extremely quickly, in milliseconds or
| microseconds, so the neutron flux would need to be much
| more intense than in nuclear explosions in order to produce
| a non-negligible equilibrium concentration.
|
| Most elements that are heavier than plutonium would decay
| before the materials containing them could aggregate into a
| planet (which may take at least a few million years). When
| the planets of the Solar System have formed, they probably
| still contained significant quantities of plutonium and
| neptunium, but then they have decayed quickly, leaving
| uranium as the heaviest surviving primordial element.
|
| While there might exist an island of stability for super-
| heavy nuclei of elements beyond any of those that have been
| synthesized artificially by ion collisions, for now there
| is no known natural process that could produce them in
| measurable quantities. By "stability" it is meant that the
| super-heavy elements might have lifetimes measured in years
| instead of milliseconds, not that they could be as stable
| as the already not very stable uranium or plutonium.
| thsksbd wrote:
| A more interesting question is if an alien race can exist with
| ratios that differ considerably from the ones on earth.
|
| Outside of carbon chemistry your ability to create replicable
| life plummets. Biologists may speculate if non carbon life is
| possible, but there's no doubt it would be limited. Arsenic or
| silicon just don't have the chemical complexity carbon does.
|
| As for super heavy elements - the elements alien races would
| have access to wouldn't be that different from ours. Heavy
| nuclei are terribly radioactive and thus short lived. The
| article points our elements heavier than 260 are too short
| lived, but on astronomical (and biological) scales anything
| past 238 (ie Uranium) is short lived.
|
| Past Uranium (which we have on Earth naturally), only Pu-244 is
| relatively long lived. Its half life is 81 million years vs.
| U-238 at 2 billion years. 81 million sounds like a long time,
| but the alien race has to evolve intelligence. We've been
| evolving for about 4 billion years, or 40 halvings of Pu-244
| initial (anyway low) concentration. 2^-40 is a small number. By
| comparison U-238 has halved only twice on Earth since evolution
| started.
|
| To illustrate, if the entire Sun were made of Pu-244 and the
| entirety of the remaining Pu-244 were put on Earth after 4
| billion years, the concentration would be less than 1 part per
| million per mass.
| blacksmith_tb wrote:
| There's been recent talk of finding a new island of
| stability[1] though I don't think we imagine those super-
| heavy elements would have half-lives of more than thousands
| of years (so probably not very handy for alien engineers).
|
| 1: https://en.wikipedia.org/wiki/Island_of_stability#Possible
| _n...
| thsksbd wrote:
| Yea, and it is super cool to think that, but either
|
| 1. the kinetic barrier is impossibly large that even novas
| cant cross it, or
|
| 2. the "stable" elements are not very long lived in
| astronomical time scales.
|
| Probably both are true, either way, it's a wash - no super
| heavy elements for alien races to play with.
| scotty79 wrote:
| > Outside of carbon chemistry your ability to create
| replicable life plummets. Biologists may speculate if non
| carbon life is possible, but there's no doubt it would be
| limited. Arsenic or silicon just don't have the chemical
| complexity carbon does.
|
| Best argument for carbon I've seen so far is that despite
| carbon being just 0.02% of all elements on earth it became
| preferred engine of life. Although I can't rule out that
| under different temperature, pressures and radiation some
| other element might be preferred if it's reasonably abundant
| somewhere. In my opinion if there's mostly stable, reasonable
| energy gradient somewhere life will find a way if possible.
| jylam wrote:
| Isn't there a probable island of stability, with very heavy,
| stable elements ?
| Sharlin wrote:
| Possible, not probable. It's a cool idea but even if the
| island is theoretically possible _and_ there's some real
| astrophysical process that could actually synthetize such
| nuclei, they'd likely still be only "stable" relative to
| other superheavy elements. That is, half-lifes from seconds
| to years or something like that rather than microseconds.
| jylam wrote:
| Ok, looked back at some stuff I read, and yes we are
| talking about half-lives of a couple of years at most.
| Disappointing, but thank you :)
| NoMoreNicksLeft wrote:
| In later years, I thought it had changed to "relatively
| stable"... as in elements that have half-lives in minutes
| rather than in milliseconds.
| didgeoridoo wrote:
| Ha, given that this is cosmologists talking, I assumed
| "extraordinarily heavy" meant... like, beryllium. Element 260 was
| a nice surprise.
| WendyTheWillow wrote:
| Similarly, I saw this and thought, "Didn't we know this
| already?" I was taught this literally a few weeks ago in my
| "Astronomy for non-STEM majors" class.
|
| But then yeah, 260 is a big number, heh.
| varjag wrote:
| Wasn't the accepted model that formation of these happens
| only in supernova events?
| Sharlin wrote:
| The article is talking about the r-process, so it's still
| supernovas (either core-collapse or more likely neutron
| star collision) that would have forged these elements.
| Ancient or not, a stably burning star isn't going to
| synthetize nuclei heavier than iron in non-negligible
| quantities.
| antognini wrote:
| Some elements are believed to only form from neutron star
| mergers.
| rdlw wrote:
| Atomic mass 260 != element 260. Bismuth-209 has atomic mass
| ~209 but is element 83 (123 neutrons add the extra mass).
|
| An atomic mass of 260 probably means about... 100-120 protons?
| That's a guess from eyeballing this chart:
| https://en.wikipedia.org/wiki/List_of_elements_by_stability_...
|
| Still very cool, but not (far) outside of what has been
| synthesized.
| borissk wrote:
| IMHO there are probably ways for heavy elements to form without
| neutron stars or supernova explosions. We have so much of these
| heavy elements in the crust of the Earth (and they tend to fall
| down towards the center when a planet is formed).
| thriftwy wrote:
| Why? It's just a large chunk of the matter in the crust of
| Earth previously went through a neutron star/supernova.
| digging wrote:
| But supernova distribution explains the amounts we have in the
| crust very well, so there's no reason to look for other
| sources.
| adamiscool8 wrote:
| So Bob Lazar was right after all, the aliens might have naturally
| sourced moscovium for their anti-gravity generators! [0][1]
|
| [0]
| https://ui.adsabs.harvard.edu/abs/2004AIPC..699.1230A/abstra...
|
| [1] https://science.howstuffworks.com/space/aliens-
| ufos/element-...
| Terr_ wrote:
| Due to the _X-Com_ franchise, some part of me will always think
| of it as Elerium-115. [0]
|
| [0] https://www.ufopaedia.org/index.php/Elerium-115
| whoopdedo wrote:
| How ancient are we talking here? Was there a time when the size
| of the universe was large enough to form stars but still much
| denser than it is today? That meant there was "more" matter
| available to those stars for crunch into large atoms.
| everdrive wrote:
| This just not a necessary fact that making the heavier elements
| takes more time, and so the more recent stars cannot make such
| heavy elements?
| antognini wrote:
| No. The massive stars that produce these elements have very
| brief lives. What's different is that the metallicity of later
| stars is higher than earlier stars. In essence, the earliest
| stars were formed from gas that had virtually no metals in them
| and because of that could grow much larger. But after their
| death, they polluted the ISM with metals which prevented later
| generations from becoming as massive.
| SpaceManNabs wrote:
| HN devolves into terrible conversations when it comes to star
| stuff.
|
| Experts thinking they are experts in other things. This thread
| reminds me of conversations every time MOND comes up.
| stainablesteel wrote:
| i've always wondered if much heavier nuclei produce different
| kinds of radiation not seen prior that produces things like dark
| matter
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