[HN Gopher] Ancient stars made extraordinarily heavy elements, r... ___________________________________________________________________ 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 ___________________________________________________________________ (page generated 2023-12-08 23:00 UTC)