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COMMENT PAGE FOR:
HTML Cosmic-ray bath in a past supernova gives birth to Earth-like planets
phkahler wrote 14 hours 13 min ago:
Why is it said that it takes a supernova to make elements heavier than
iron? You're not going to get iron-iron fusion, but what about
proton-iron fusion or similar? Also, we can make reactors here on
earth that convert Thorium into Uranium, and we can also make plutonium
in a proper reactor. We mustn't confuse reactions useful for power
production with reactions for element production right? Why can't a
regular star produce some heavy elements?
largbae wrote 13 hours 56 min ago:
I think you're right that heavier elements can be made, it's just
energy negative to do so. But without a nova they would never leave
the inside of the star to find their way into a new planet.
pfdietz wrote 13 hours 38 min ago:
But they do leave. Stars not large enough to go supernova do still
form planetary nebulas when the more gradually lose their outer
layers to space. Only the core is left behind to form a white
dwarf. This will be the Sun's eventual fate.
pixl97 wrote 12 hours 6 min ago:
I mean it's not hard to do spectrometry on said nebula, and I
don't think there is near enough heavier matter detected there.
pfdietz wrote 11 hours 54 min ago:
s-process elements (including radioactive ones like technetium)
are detected in the spectra of the stars where the process
occurs, which means they are right out at the "surface".
MattPalmer1086 wrote 12 hours 23 min ago:
Wouldn't the heavier elements generally sink to the core and the
outer layers be composed of the lighter ones?
pfdietz wrote 11 hours 56 min ago:
No, gravitational segregation like that is a very slow process
and would be overwhelmed by any convection. In Earth's
atmosphere, for example, it doesn't occur until very high
altitude (80 km or so) where diffusion is fast enough to
overcome mixing.
pfdietz wrote 7 hours 8 min ago:
See also "dredge-up". [1] "By definition, during a dredge-up,
a convection zone extends all the way from the star's surface
down to the layers of material that have undergone fusion."
HTML [1]: https://en.wikipedia.org/wiki/Dredge-up
MattPalmer1086 wrote 1 hour 44 min ago:
That seems to cover elements up to carbon. Not sure
heavier elements would be convected?
bjelkeman-again wrote 13 hours 58 min ago:
âElements heavier than iron, up to bismuth, are primarily produced
via the s-process (slow neutron capture) in low to medium-mass stars
during their later evolutionary stages.
The remaining and heaviest elements (beyond iron and bismuth) are
formed through explosive events: core-collapse supernovae generate
elements between neon and nickel, while the r-process (rapid neutron
capture) in supernovae and, predominantly, neutron star mergers
creates elements like uranium and thorium, dispersing them into the
interstellar medium for planetary formation.â
From
HTML [1]: https://www.astronomy.com/science/the-universes-guide-to-cre...
jmyeet wrote 16 hours 30 min ago:
The Universe coalesced into hydrogen and helium from a quark-gluon
plasma soon after the Big Bang. It's kind of staggering the sequence of
events that occurred afterwards to bring us here.
As many of us know, the fusion in stars produces elements as heavy as
iron. It then takes explosions of those stars to scatter those elements
into space, ultimately bringing them into the protoplanetary disc of a
new star, such that it can form a planet in the right zone. That star
then needs to live long enough and the system needs to be stable enough
to produce complex life.
But it gets worse because we obviously have elements heavier than iron.
So stars of a sufficient size need to form such that when the stars die
they do so in an even more violent fashion. The core needs to collapse
into neutronium and the resultant supernova can produce heavier
elements. They also come from neutron star mergers.
So all the uranium we have on Earth came from such an event. Because of
the nuclear decay chain we can estimate when this uranium was made and
IIRC that's somewhere between 80 and 200 million years before the Earth
formed.
So this all had to happen sufficiently close to the Sun and that
material had to be captured in the Sun's protoplanetary disc. We needed
the right combination of elements to form a protective magnetic field
and produce enough but not too much heat.
We're going to keep discovering mechanisms like this and the importance
of particular isotopes, events and things like how amino acids seem to
form relatively easily (given the right elements are present), which
itself is a consequence of CNO fusion.
But also why did the Sun form at all? It has to be in a nebula of
largely hydrogen and helium and something had to trigger that like the
shock wave from a nearby supernova or neutron star or black hole
merger.
It's kind of why I think sentient life is incredibly rare.
zackmorris wrote 14 hours 4 min ago:
> It's kind of why I think sentient life is incredibly rare.
They just found the building blocks of life in asteroid Bennu: [1]
[2] âSo far we have not seen any evidence for a preferred
chirality,â (Dan) Glavin says (important for understanding why
amino acids on Earth seem to all be left-handed): [3] Life is
probably abundant everywhere in the universe. Also, evolution seems
to spring up everywhere, in any system of sufficiently advanced
complexity, regardless of what substrate it operates on. So I think
that we'll start seeing life-like emergent behavior in computing,
especially quantum computing, in the next 5-10 years.
So the question becomes: what great filter (in the sense of the Drake
equation and Fermi's paradox) causes life as we know it to go dark or
wipe itself out just after it achieves sentience?
Well, we're finding out the answer right now. Life probably merges
with AI and moves into what could be thought of as another dimension.
Where time moves, say, a million times faster than our wall clock
time, so that it lives out lifetimes in a matter of seconds. Life
everywhere that managed to survive probably ascended when it entered
the matrix. So that by now, after billions of years since the first
life did this and learned all of the answers, we're considered so
primitive that Earth is just a zoo for aliens.
Or to rephrase, omnipotent consciousness probably gets bored and
drops out of the matrix periodically to experience mortal life in
places like Earth. So simulation theory probably isn't real, but
divine intervention might be.
HTML [1]: https://science.nasa.gov/mission/osiris-rex/
HTML [2]: https://physicsworld.com/a/components-of-rna-among-lifes-bui...
HTML [3]: https://physicsworld.com/a/asteroid-bennu-contains-the-stuff...
jmyeet wrote 13 hours 26 min ago:
> Life is probably abundant everywhere in the universe.
I'm not convinced of that. Yes it seems like the building blocks
are abundant but there's so many steps beyond that to get to
abundant life.
The first life we had in the Archeaen era was dependant on sulfur,
which was concentrated around volcanic vents so this already
presumes a lot, namely oceans and a geologically active planet.
Oxygen leeched a bunch of minerals into the water.
And then came cyanobacteria who no longer needed volcano but had
this annoying habit of producing a new waste product: oxygen. This
both absolutely killed all the Archeaen life but also cleansed the
oceans as ions like iron precipitated into ferric oxide and we can
see the layers of these cycles in the rock.
So the Earth needed all these elements and the Sun and Solar System
needed to be sufficiently stable for billions of years just to get
to this point and there are so many steps beyond this.
I personally believe it's more likely than not that we are the only
potentially spacefaring civilization in our entire galaxy.
estimator7292 wrote 9 hours 46 min ago:
This all hinges on the presupposition that our solar system is
unique in its configuration and location in the galaxy.
We haven't surveyed nearly enough other planetary systems to have
any real idea if our system is unique. We barely have the ability
to even see systems like ours in the first place. There's so
little data available that it's not reasonable to draw a
conclusion either way.
01100011 wrote 14 hours 12 min ago:
Surely someone has proposed the existence of a civilization forming
from <=iron and making the heavier elements themselves? Seems far
fetched but you have quite a bit of time to play with there.
jmyeet wrote 6 hours 5 min ago:
So here's a fun experiment for you. Look at a periodic table and
start with Cobalt (the first element after Iron) and look at what
its uses are. Wikipedia is fine. And then ask if there are
alternatives for that metal. In some cases we won't know but in
other cases, the situation would be dire.
The first few include Nickel, Copper and Zinc. Think of all those
alloys and direct uses, particularly copper as an electrical
conductor. Or all the rare earths for magnets and semiconductors.
Or gold or lead even.
Then there's Iodine, which is actually essential for human life.
Zinc, selenium and others are used too, possibly others.
The scarier question is what happens when the universe runs out of
hydrogen in vast quantities? It will only be around for stars to
burn for so long. Most are in the billions of years. A handful are
in the trillions. But eventually they will run out too.
mcswell wrote 7 hours 1 min ago:
Obviously this doesn't answer your question, but there are scifi
stories about alien civilizations that arise on planets without
heavy metals. Usually the plot revolves around their not getting
past the stone age.
BurningFrog wrote 14 hours 23 min ago:
> But also why did the Sun form at all?
I don't understand the question. There must have been a cloud of gas
big and dense enough to provide the mass for the solar system.
Once that exists gravity does the rest, right?
> all the uranium we have on Earth came from such an event
That must mean the Sun also has its fair share of that Uranium? Or
maybe more of it, since the heavy elements were more drawn to the
center of the solar system?
mr_toad wrote 10 hours 39 min ago:
> I don't understand the question. There must have been a cloud of
gas big and dense enough to provide the mass for the solar system.
Once that exists gravity does the rest, right?
Very large clouds of gas can exist with gravitation attraction
balanced by gas pressure. This delicate balance can be disturbed
by passing stars, supernovae, galactic mergers and other events.
pixl97 wrote 12 hours 1 min ago:
>That must mean the Sun also has its fair share of that Uranium?
That's a good question. I would assume the sun captured a whole
pile of uranium around the time the earth was forming. And it
likely sunk to the core. The question is what happened then. The
core area is dense enough to fuse hydrogen into helium, without any
calculation I'd guess a lot of this is now in much smaller elements
as there are a lot of neutrons to break it apart.
lawlessone wrote 11 hours 13 min ago:
going on tangent here but Przybylskis Star might be relevant.
HTML [1]: https://en.wikipedia.org/wiki/Przybylski%27s_Star#Chemic...
marcus_holmes wrote 8 hours 15 min ago:
great rabbit hole, thanks :)
kakacik wrote 15 hours 24 min ago:
Incredibly rare X maybe a trillion planets(oids) in our galaxy X
maybe a trillion galaxies in whole universe may change the outcome a
bit.
Of course if speed of light is the hard unavoidable limit it doesnt
matter now or for next few trillions of years. Eventually though, if
it will keep expanding, the only important thing in universe will be
energy. Species that will grok that first may decide to not share and
take it all for themselves. Although sustainability of some empire
over 10^10^10^10 years and further... its something even my otherwide
vivid imagination can't concieve.
dhosek wrote 15 hours 2 min ago:
If I was going to design a universe where multiple intelligences
would evolve but never interact, this one would meet the
requirements quite well.
mr_mitm wrote 15 hours 5 min ago:
Not if incredibly rare is something like 10^-30
jcims wrote 15 hours 28 min ago:
>It's kind of why I think sentient life is incredibly rare.
Agreed. The universe is big, but combinatorics are bigger.
I'd be disappointed but ultimately unsurprised if an all-knowing
oracle said it has only happened once in the history of the universe.
My follow up question, of course, would be whether or not it
happened on Earth.
buu700 wrote 14 hours 58 min ago:
Turns out "God" was just a convenient shorthand for "alien AI", and
Genesis was about terraforming and seeding life on Earth.
jcims wrote 13 hours 28 min ago:
Eden would be a great name for a sterile yet fertile planet
waiting for a visitor.
kldavis4 wrote 15 hours 41 min ago:
> So this all had to happen sufficiently close to the Sun and that
material had to be captured in the Sun's protoplanetary disc. We
needed the right combination of elements to form a protective
magnetic field and produce enough but not too much heat.
any idea how close? like 10s of light years or what?
pfdietz wrote 11 hours 48 min ago:
Not just captured; some of the isotopes were formed in situ by
bombardment of the protoplanetary disk by ~GeV range protons formed
in the supernova shock by the Fermi mechanism (basically, bounce
particles back and forth between moving magnetic mirrors and their
energy gradually but exponentially increases.)
MarkusQ wrote 15 hours 33 min ago:
According to the article, ~1 parsec, or something like 1-10 light
years (further, less effect; closer, you disrupt the protoplanetary
disk).
moktonar wrote 16 hours 16 min ago:
And yet, inevitable. Thatâs why a simulation of the universe would
be a secure way of creating AGI in the true sense. All depends on:
can you find an algorithm that simulates quantum physics efficiently,
or, can you make a quantum computer with sufficiently many qbits?
lanyard-textile wrote 15 hours 40 min ago:
... huh, wow.
Talk about sublimity.
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