Ancient stars made extraordinarily heavy elements, researchers find | Hacker News Reader

Ancient stars made extraordinarily heavy elements, researchers find

phys.org

131 pointswglb55 comments

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.

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...

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

I don't find it surprising at all considering how highly regulated anything involving uranium is: mining, storage, enrichment, actual use as weapons or power generators.

Look what effort we went into the last two decades trying to stop Iran from developing their uranium enrichment infrastructure.

Then back in WW2 we did a complete covert op to sabotage the heavy water (used in enrichment) generators in the mountains of Norway just to stop the Germans or Stalin from getting access to weapons grade material.

Hell, they only even had some tons set aside by accident to enrich in the first place.

Anyways, finding already fissled uranium material probably set off many alarm bells at the Pentagon and the Atomic Energy Commission in 1972.

"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...

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.

If the Cambrian explosion had happened sooner, then this would have been possible.

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.

> 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?

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).

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?)

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.

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...

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.

> 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.

Might the low abundance of carbon on Earth compared to its ubiquity in biology be suggestive of some kind of panspermia?

Although carbon is relatively scarce on Earth, it is the fourth most common element by mass in the universe (and in Earth's solar system) [1].

The four most common elements in the human body are the same as the four most common elements in the universe, albeit in different proportions [2].

[1] https://en.wikipedia.org/wiki/Abundance_of_the_elements#Univ...

[2] https://en.wikipedia.org/wiki/Abundance_of_the_elements#Huma...

is there a known reason carbon is so scarce on earth compared to the rest of the solar system?

This doesn't seem to have been firmly established, but as far as I can tell it's currently thought to be related to how carbon in the solar system's protoplanetary disk behaved when it was vaporized after fusion began in the sun. The question was studied in this paper published in 2021 [1], which is discussed in this article [2].

The authors of the paper suggest that the material that formed the Earth was depleted of carbon early in the solar system's history due to solar activity, and that most of the carbon now on Earth was delivered to the planet later on directly from the interstellar medium.

I should note a couple of clarifications to my first comment: the elemental abundance I mentioned for the universe and Earth's solar system does not include helium and neon, which are abundant, but are usually ignored in this context as they're noble gases.

There is also estimated to be slightly more mass in the present-day universe in the form of iron than nitrogen due to the high mass of iron atoms (nitrogen is the fourth most abundant element by mass in the human body, but the body contains relatively little iron). The number of nitrogen atoms in the universe, however, is substantially higher than the number of iron atoms. The amount of iron in the early universe should also have been lower; the element is formed late in the stellar life cycle [3], whereas the other cosmologically abundant elements that are relevant to biology (carbon, nitrogen and oxygen) are formed earlier [4].

[1] https://arxiv.org/abs/2104.02702

[2] https://phys.org/news/2021-04-stardust-pale-blue-dot-carbon....

[3] https://en.wikipedia.org/wiki/Iron#Cosmogenesis

[4] https://en.wikipedia.org/wiki/CNO_cycle

it could be that carbon-based life somehow pre-empts x-based life when carbon exists in the environment, even if there’s more of x

Sure, as a matter of logic in the absence of chemical knowledge.

Once you study the various elements and realize that carbons' chemistry is uniquely rich with a set of capabilities other elements lack non carbon replication becomes meh.

Silicon comes close, but the energies suck, elemental Si is too stable, and its oxide a solid.

> oxide a solid

At room temperature and pressure of rooms built by beings made of carbon.

But we know what happens at temperatures and pressures -> things break down and become less interesting.

SiO2 is quartz. At a T high enough to melt it (never mind a vaporize it to have a cycle analogous to the C-CO2 cycle), Si chemistry breaks down.

Carbon chemistry is unique because it occupies a unique chemical niche. It makes interesting and stable compounds at T high enough to have appreciable rates, but low enough that things don't just rip themselves apart.

Not to mention at T high enough to vaporize SiO2 you won't have water, which is a pretty nifty solvent for life to have.

Think of it this way. We know the bond strength of the various chemical bondings. We cant get around that and each type of bonding is responsible for several unique and fundamental moiety in biological replication.

> Not to mention at T high enough to vaporize SiO2 you won't have water, which is a pretty nifty solvent for life to have.

Yeah, not even iron could work as a solvent at that temperature.

the logic here is extremely iffy

Sorry, to avoid embarrassment I didn't include the conclusion:

Since, as stated, non-carbon chemistry is limited, non-carbon life (very broadly defined as replication of information) is either impossible or incredibly boring.

but this is what I’m saying. perhaps it’s possible to have life from other elements, but carbon-based life simply dominates it to a degree that it doesn’t survive

Water worlds intrigue me. All the elements and heat vents you might need for life.

But how do you develop the technology for an escape velocity civilization in a medium so corrosive and viscous?

Super Earths are a likely source of water worlds, since the same percentage of water volume (~ to radius^3) results in much deeper oceans at the surface (~ to radius^2). The greater gravity would create even more hurdles. How do you hit escape velocity if your fuel to orbit is to heavy to lift itself? First orbital vehicle might have to be nuclear.

Problem 1: Develop a civilization with a sustained technology runway in a medium that corrodes, relentlessly saps temperature gradients, creates immense pressure at its solid floor, etc.

Problem 2: Create floating platforms and colonize their ocean surface.

Problem 3: Develop atmospheric flight, from their bobbing surface colonies, with heavy water filled planes.

Problem 4: Develop orbital flight with water filled space craft.

Problem 5: Develop sustainable water filled living environments off planet, as first step to going beyond.

And do this before their star or other cause finishes them off!

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.

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.

Well we know how stable many of them are - we've synthesized them and out them in our fire alarms

Isn't there a probable island of stability, with very heavy, stable elements ?

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.

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 :)

In later years, I thought it had changed to "relatively stable"... as in elements that have half-lives in minutes rather than in milliseconds.

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-...

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

Awesome franchise. I'm still waiting for X-Com 3 after these years.

Ha, given that this is cosmologists talking, I assumed “extraordinarily heavy” meant… like, beryllium. Element 260 was a nice surprise.

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.

Ah yep, misread “atomic mass” as “atomic number”.

Still, decently heavy :)

260 would be falling short to fall short of the island of stability

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.

Wasn't the accepted model that formation of these happens only in supernova events?

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.

Some elements are believed to only form from neutron star mergers.

What “causes” spontaneous decay? Neutrons can cause fission — can protons also cause it? Can anything else facilitate or inhibit nuclear decay?

“We don’t know” or “it’s spontaneous” is the definitive answer for what gives an unstable atom its nudge.

https://physics.stackexchange.com/questions/497589/what-trig...

https://www.thoughtco.com/why-radioactive-decay-occurs-60864...

I personally don’t like the answer that it’s “spontaneous”, but I vaguely grok that any explanation has to step beyond QM/QCD as we know it.

There are hidden variable QM interpretations that exist, but marrying them with Special Relativity appears to be difficult.

There are even more exotic hidden variables theories like https://physics.stackexchange.com/questions/515720/what-is-t...

but none of these variables are measurable with regards to making predictions on decay.

I’m also way out of my field so I may be wrong here.

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.

I am thinking these are the first stars formed after the Big Bang (when there was only Hydrogen and Helium and some Lithium), but those stars don't live very long.

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).

Why? It's just a large chunk of the matter in the crust of Earth previously went through a neutron star/supernova.

But supernova distribution explains the amounts we have in the crust very well, so there's no reason to look for other sources.

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?

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.

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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