8 ms·

How did elements created by a merging neutron stars and dying low-mass stars get down to our planet?

mc32 6y ago
Time? They had like 10 billion years to diffuse and propagate I guess...
AllegedAlec 6y ago
Our sun is about 4.6B year old. There were a few other generations of stars that lived and died before our sun came about, and these spewed out the heavier elements that make up our solar system.
- Tepix 6y ago
  It must have been a somewhat dull first generation of stars and planets with only Hydrogen and Helium around. On the other hand, giant stars explode after just a few million years so it didn't take long for other elements to appear.
  - dredmorbius 6y ago
    The ratio of heavier elements to H & He is called metallicity, and it is a measurable characteristic of stars, which are classed into Type I (high metallicity) and Type II (low) populations. Low-metallicity Type II stars are generally older. Nothing specific on what Type II stellar systems and planets would be like, though I'd suspect gas giants, generally. https://en.wikipedia.org/wiki/Metallicity https://en.wikipedia.org/wiki/Metallicity
  - saagarjha 6y ago
    I think they make up for their dullness by being absolutely massive–hundreds of solar masses, if not more.
BurningFrog 6y ago
They didn't land on the planet, they formed it.
- ncmncm 6y ago
  Some did, some didn't. All the iridium, platinum, gold we find landed.
  - Diederich 6y ago
    > All the iridium, platinum, gold we find landed Cool. Do you have a quick reference for the 'landed' part? As opposed to being part of the planet from the beginning. Thanks!
    - dredmorbius 6y ago
      https://www.livescience.com/15938-earth-precious-metals-space-origin.html https://www.livescience.com/15938-earth-precious-metals-spac... https://www.oakton.edu/user/4/billtong/eas100/cosmicorigins.htm https://www.oakton.edu/user/4/billtong/eas100/cosmicorigins....
  - BurningFrog 6y ago
    I've been wondering about that. Is it because all heavy elements present when Earth formed sank to the center? That would make sense, but I've assumed that since we can mine gold, that's not what happened. If all the gold fell from the sky, that would explain things.
Sharlin 6y ago
Neutron star merger is a rather energetic event, ejecting copious amounts of matter. Dying low-mass stars (like the sun) eject their outer envelope, forming an expanding nebula.
Tuna-Fish 6y ago
Two neutron stars merging is an extremely energetic event which emits vast amounts of degenerate neutron star material at speeds above escape velocity. Pretty much instantly after this material is liberated from the pressure and gravity of the neutron star, it starts decaying into normal matter, producing a vast menagerie of (generally very neutron-rich) elements, which then follow their decay chains until they end up as mostly stable elements. Low-mass stars, like the Sun, will generally expand into many times their original size after hydrogen starts running out in their core. Much of these tenuous outer layers will be emitted during the final stages of the star, before the core collapses into a white dwarf.
- arethuza 6y ago
  "it starts decaying into normal matter" Thanks - I had managed to miss the fact that being made in a neutron star collision implies that things like gold were once part of neutron stars. I think this exceeds the coolness of having been in a supernova.
  - ahazred8ta 6y ago
    The collision is messy and it splatters a huge amount of neutronium into space. This dissociates into a very hot mist of heavy elements, which eventually mixes into the surrounding nebula. The proto-solar disk was formed from this mixture.
- ninkendo 6y ago
  I've always wondered, does the presence of heavy elements on earth (ones which are likely to have formed via neutron star mergers) indicate that a pair of neutron stars merged relatively nearby our sun when it formed? Or is there just a diffuse amount of these elements in typical protostellar clouds all over the galaxy? Perhaps a simpler way of asking: are the heavy elements we find on earth typical for an average planet? Or does a planetary system have to be "lucky" enough to have formed near a neutron star merger, for it to have elements like gold in measurable quantities?
hermitcrab 6y ago
The follow up question is, how come the different elements aren't uniformly mixed within the earth. Or perhaps formed into stratified layers with the densest at the centre? E.g. Why are there 'deposits' of gold relatively close to the surface? Something to do with interaction of the physical and chemical properties of the elements with local variations in conditions?
- changoplatanero 6y ago
  Yes you're right. Geologic and biologic processes unevenly distribute the elements
  - HarryHirsch 6y ago
    The keyword is "Goldschmidt classification": https://en.wikipedia.org/wiki/Goldschmidt_classification https://en.wikipedia.org/wiki/Goldschmidt_classification Those who would like to know more could do worse than pick up Greenwood's & Earnshaw's book (this one: https://www.amazon.com/-/dp/0750633654 https://www.amazon.com/-/dp/0750633654) from the nearest university library, it has a chapter on nucleogenesis and cosmic and geologic abundances.
- ncmncm 6y ago
  All Earth's primordial gold sank. So, all the gold we find or mine came from meteorites (including dust) after solidification. Most has been dissolved in water.
- dredmorbius 6y ago
  The Earth is mostly stratified: light rocky silicate crust, heavier (though also rocky) magnesium-silicate mantle, core of mostly nickle-iron and heavier elements, which formed during the iron catastrophe. Crustal deposits of heavier minerals largely result from late bombardment (after the crust had formed, about 100 million years after Earth's formation itself), geothermal and tectonic activity (volcanism, rift zones, vents), and biological mobilisation and concentration (e.g., lighter elements in coal and limestone, but notably, banded iron formations). Events such as the hypothesized Tethys collision could of course also have influenced distribution. Gold forms veins typically in quartzes through differential precipitation AFAIU. Ore formation is its own fascinating subfield of geology, and is underappreciated by many advocates of space mining. https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth... https://en.wikipedia.org/wiki/Planetary_differentiation https://en.wikipedia.org/wiki/Planetary_differentiation https://en.wikipedia.org/wiki/Iron_catastrophe https://en.wikipedia.org/wiki/Iron_catastrophe https://en.wikipedia.org/wiki/Ore_genesis https://en.wikipedia.org/wiki/Ore_genesis

mc32 6y ago

Time? They had like 10 billion years to diffuse and propagate I guess...

Our sun is about 4.6B year old. There were a few other generations of stars that lived and died before our sun came about, and these spewed out the heavier elements that make up our solar system.

Tepix 6y ago
It must have been a somewhat dull first generation of stars and planets with only Hydrogen and Helium around. On the other hand, giant stars explode after just a few million years so it didn't take long for other elements to appear.
- dredmorbius 6y ago
  The ratio of heavier elements to H & He is called metallicity, and it is a measurable characteristic of stars, which are classed into Type I (high metallicity) and Type II (low) populations. Low-metallicity Type II stars are generally older. Nothing specific on what Type II stellar systems and planets would be like, though I'd suspect gas giants, generally. https://en.wikipedia.org/wiki/Metallicity https://en.wikipedia.org/wiki/Metallicity
- saagarjha 6y ago
  I think they make up for their dullness by being absolutely massive–hundreds of solar masses, if not more.

BurningFrog 6y ago

They didn't land on the planet, they formed it.

ncmncm 6y ago
Some did, some didn't. All the iridium, platinum, gold we find landed.
- Diederich 6y ago
  > All the iridium, platinum, gold we find landed Cool. Do you have a quick reference for the 'landed' part? As opposed to being part of the planet from the beginning. Thanks!
  - dredmorbius 6y ago
    https://www.livescience.com/15938-earth-precious-metals-space-origin.html https://www.livescience.com/15938-earth-precious-metals-spac... https://www.oakton.edu/user/4/billtong/eas100/cosmicorigins.htm https://www.oakton.edu/user/4/billtong/eas100/cosmicorigins....
- BurningFrog 6y ago
  I've been wondering about that. Is it because all heavy elements present when Earth formed sank to the center? That would make sense, but I've assumed that since we can mine gold, that's not what happened. If all the gold fell from the sky, that would explain things.

Sharlin 6y ago

Neutron star merger is a rather energetic event, ejecting copious amounts of matter. Dying low-mass stars (like the sun) eject their outer envelope, forming an expanding nebula.

Tuna-Fish 6y ago

Two neutron stars merging is an extremely energetic event which emits vast amounts of degenerate neutron star material at speeds above escape velocity. Pretty much instantly after this material is liberated from the pressure and gravity of the neutron star, it starts decaying into normal matter, producing a vast menagerie of (generally very neutron-rich) elements, which then follow their decay chains until they end up as mostly stable elements. Low-mass stars, like the Sun, will generally expand into many times their original size after hydrogen starts running out in their core. Much of these tenuous outer layers will be emitted during the final stages of the star, before the core collapses into a white dwarf.

arethuza 6y ago
"it starts decaying into normal matter" Thanks - I had managed to miss the fact that being made in a neutron star collision implies that things like gold were once part of neutron stars. I think this exceeds the coolness of having been in a supernova.
- ahazred8ta 6y ago
  The collision is messy and it splatters a huge amount of neutronium into space. This dissociates into a very hot mist of heavy elements, which eventually mixes into the surrounding nebula. The proto-solar disk was formed from this mixture.
ninkendo 6y ago
I've always wondered, does the presence of heavy elements on earth (ones which are likely to have formed via neutron star mergers) indicate that a pair of neutron stars merged relatively nearby our sun when it formed? Or is there just a diffuse amount of these elements in typical protostellar clouds all over the galaxy? Perhaps a simpler way of asking: are the heavy elements we find on earth typical for an average planet? Or does a planetary system have to be "lucky" enough to have formed near a neutron star merger, for it to have elements like gold in measurable quantities?

hermitcrab 6y ago

The follow up question is, how come the different elements aren't uniformly mixed within the earth. Or perhaps formed into stratified layers with the densest at the centre? E.g. Why are there 'deposits' of gold relatively close to the surface? Something to do with interaction of the physical and chemical properties of the elements with local variations in conditions?

changoplatanero 6y ago
Yes you're right. Geologic and biologic processes unevenly distribute the elements
- HarryHirsch 6y ago
  The keyword is "Goldschmidt classification": https://en.wikipedia.org/wiki/Goldschmidt_classification https://en.wikipedia.org/wiki/Goldschmidt_classification Those who would like to know more could do worse than pick up Greenwood's & Earnshaw's book (this one: https://www.amazon.com/-/dp/0750633654 https://www.amazon.com/-/dp/0750633654) from the nearest university library, it has a chapter on nucleogenesis and cosmic and geologic abundances.
ncmncm 6y ago
All Earth's primordial gold sank. So, all the gold we find or mine came from meteorites (including dust) after solidification. Most has been dissolved in water.
dredmorbius 6y ago
The Earth is mostly stratified: light rocky silicate crust, heavier (though also rocky) magnesium-silicate mantle, core of mostly nickle-iron and heavier elements, which formed during the iron catastrophe. Crustal deposits of heavier minerals largely result from late bombardment (after the crust had formed, about 100 million years after Earth's formation itself), geothermal and tectonic activity (volcanism, rift zones, vents), and biological mobilisation and concentration (e.g., lighter elements in coal and limestone, but notably, banded iron formations). Events such as the hypothesized Tethys collision could of course also have influenced distribution. Gold forms veins typically in quartzes through differential precipitation AFAIU. Ore formation is its own fascinating subfield of geology, and is underappreciated by many advocates of space mining. https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth... https://en.wikipedia.org/wiki/Planetary_differentiation https://en.wikipedia.org/wiki/Planetary_differentiation https://en.wikipedia.org/wiki/Iron_catastrophe https://en.wikipedia.org/wiki/Iron_catastrophe https://en.wikipedia.org/wiki/Ore_genesis https://en.wikipedia.org/wiki/Ore_genesis