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  “The nitrogen in our DNA, 
  the calcium in our teeth, 
  the iron in our blood, 
  the carbon in our apple pies
  were made in the interiors of collapsing stars.
  We are made of star stuff”.
  – Carl Sagan

  We have calcium in our bones, 
  iron in our veins, 
  carbon in our souls, 
  and nitrogen in our brains.
  93 percent stardust,
  with souls made of flames, 
  we are all just stars 
  that have people names"
  Nikita Gill

I understand this is a poem that is focused on artistic expression and not scientific accuracy, but I find the line about “carbon in our souls” to be out of place. I guess the rest of the poem is incidentally correct (when not abstract)

One who is a materialist could argue that your "soul" comes from the stuff you're made out of, so your "soul" probably has carbon it somewhere.

Sure, the word “soul” comes from the proto Germanic “saiwiz” (for sea or ocean).

But not because “you are like a drop in the ocean,” but because “you are like an ocean in a drop.”

The idea of soul can be objectionable when it is based on an immortal being or on a vitalist life-force (like “anima” of the Latin). But it seems fine when it is based on the psyche (like the “Psuche” of the Greek).

I embrace taboo words like soul because they 1. are common 2. are useful for referring to things that seem pretty important (like avoiding soulless companies or products or buildings) and 3. are challenging to my normal (scientific) understanding of the world.

Still, I’d be more comfortable if the poem referred to the “carbon of our souls” rather than “carbon in our souls.” Hmm…

You could define soul as the fuel engine for life, which is basically burning carbon. As long as that furnace is functioning you're alive == you have a soul.

>Carbon in our souls

I think it might be an allusion to alchemy. Basically, the alchemists believed that ash (what was left after burning something) was the soul of all things...And-- this is where my complete lack of understanding about science shows-- I'm pretty sure Ash has lots of carbon? It's, you know, poetic. Many have claimed that poems are the "language of paradox" so it's okay for it to be a little non-literal. My interpretation of it, though, is that the soul is something impure that you must burn away, or maybe that the soul is polluted by our own words and behavior. It's definitely not meant to be scientifically accurate.

ash has no carbon

carbon's oxides are all gaseous at standard temperature and pressure

Not quite. Plenty of carbon is release as carbon oxides, but calcium carbonate is also a major component of ash (or at least wood ash).

good point

little carbon, then, not none

Going by what wikipedia says, wood ash can have carbon. If I understand correctly, how much depends largely on how hot it burned.

https://en.wikipedia.org/wiki/Wood_ash#Elemental_analysis

I find this poem inaccurate.

?

Souls are clearly not made of both carbon and flames.

The ones in Hell could be.

Was that originally in a different language? "Heart" makes more sense than "soul", and could be translates loosely.

Oh wait I can play this game:

You and I are complicated but we're made of elements Like a box of paints that are mixed to make every shade They either combine to make a chemical compound or stand alone as they are

- They Might Be Giants

It’s funny that alchemy was kinda onto something, but underestimated the energy requirements by orders of magnitude of orders of magnitude

True, all you need to turn lead into gold is a moderately powerful collider and some hydrogen.

The conversion is also very slow. And expensive. To make it this way it would cost a Quadrillion dollars an ounce.

https://www.scientificamerican.com/article/fact-or-fiction-l...

Quadrillion now, but costs will drive down and once is turned to gold, it stays gold. In the far future where all gold was mined this will be the only process left to get more. Or explode stars and capture gold from them.

I joke with my Son all the time about turning Mercury into gold (He works in the nuclear industry).

Once you get past the enormous energy costs to do this you have a secondary problem, all the gold produced this way is radioactive and it beta decays to.. Mercury.

Actually current modeling has supernovae as being only a small contributor to the measured abundance of heavy nucleii. These guys tend to come from a more exotic source still: material thrown off as a neutron star is tidally disrupted during a merger event with another neutron star or black hole.

The wikipedia page is pretty good, as always: https://en.wikipedia.org/wiki/Nucleosynthesis

Almost everything with mass of 90 or above comes predominantly from neutron star mergers, basically.

Good Lord the universe is old. To think of how rare all that must be and how it had to have time to somehow get here to our planet.

If they weren't here, we wouldn't be able to talk about it.

I'd be interested to know if we're in an element rich vein of the wider universe or if all the good stuff is more or less evenly distributed?

I'm not sure but this has some interesting info such as-

>Some whole galaxies have average metallicities only 1/10 of the Sun's. Some new stars in our galaxy have more metals in them than the original solar nebula that birthed the Sun and the planets did. So the amount of "metals" like oxygen and carbon can vary by a few orders of magnitude from star to star, depending upon it's age and history.

https://www.reddit.com/r/askscience/comments/9tujxn/are_the_...

Phosphorus is supposed to be rare in the wider world. Considering how central it is to everything important, life might find it very difficult to start in our temperature range, without.

After all, is there anything better to create new elements than a hot, dense neutron soup?

I'm always fascinated by the sheer and unfathomable amounts of energy that is thrown around in these events. Just thinking about the fact that a single spoonful of neutron star matter contains more mass than Mount Everest fills me with wonder about the world we live in.

What happens whena tablespoon of neutron soup gets thrown out of the well of a neutron star? Does it suddenly expand to the size of everest? Where do the electrons come from?

I'd imagine some of the energy and degenerate matter consisting of neutrons would convert to protons and electrons, and nucleosynthesis would take place to form elements.

I have no idea, though, but I'm pretty sure I watched a video about this.

In terms of "where do the electrons come from", an ordinary neutron in free space has a half-life of about 10 minutes, decaying through beta decay which produces a proton, an electron and a neutrino.

That sounds fairly energetic... So after 10min you'd have some odd mix of heavy elements probably approaching a decent fraction of the volume of everest. Half the volume of everest x (densityofgranite / densityoflead)

That kind of expansion rate has to rival any explosion imaginable.

It's essentially a giant atomic nucleus, so absent a star's worth of gravity holding it together it's going to decay rapidly into stable isotopes. So essentially it would act more or less the same as a huge fission bomb of the same mass.

So that means that for life to form, we probably need a star to die so that the heavier atoms used in complicated life forming chemical reactions (correct me if i am wrong here as what I'm about to say depends on it), hence it could be the case that if the universe is 13.5 billion years old, then we humans are appearing in the universe at the earliest possible time.

13.5 billion years seems like the time required to create a star, have the star die and blow up, have all that material settle and create a new star, then the planets are formed, than enough time on one of those planets needs to pass for life to form, then complicated life.

I have zero ability to answer your question but I would love to know about about this. If life (like we know it) requires the explosion of aged stars, what is the earliest it would take. What is the minimum time needed to form, grow and explode a single star? Has there been time for this to occur 10s, 100s of times since the Big Bang? (obviously they can happen in parallel, but I'm thinking about how many in series).

There's a large range of stellar lifetimes, from a few million years up to trillions of years.

I'm just a layman but I believe by the time our sun has formed, we've gone through multiple star cycles. The early stars were very pure - made basically purely of hydrogen (maybe some helium?). They were huge, burned very bright and died comparatively quickly. Each time stars died, more heavy elements (and heavier elements than before) were produced. Over time the heavy element content (called metallicity) has increased in all stars. I believe there are also theories of white dwarf mergers undergoing runaway fusion and a lot of heavy elements being generated during the explosion.

You raise an interesting question though: what is the earlier point of time where the heavy elements were abundant enough for life (as we know it) to form? Just because we started existing at +13.5 billion years, it doesn't mean carbon based life couldn't have formed much earlier.

Not necessarily. First generation stars were, theoretically, enormous both due to low metallicity of the collapsed medium and a higher average concentration of said medium. These stars lifespans were extremely short, shorter that blue giants we see today. So novas due to the death of these stars happened fairly early in the lifespan of the universe (talking about few million years after the big bang).

Therefore, life could have developed in a few tens to few hundreds of millions of years after the big bang. That's still true even if we assume that heavier elements are created mainly when neutron stars collide and not by super/hypernovas as we theorized before LIGO/Virgo observatories.

Consequently, we likely are not a "progenitor" civilization in the universe if we only consider planets formation. We might not see anyone out there either because there's a great filter for intelligent life to emerge (so the bottleneck is in our past) or because few/no civilizations get to have an impact on their host stars (the filter is in our future) that would allow us to see them.

Basic life (single-celled?) requiring the elements above lead might have a chance at that time, but complex life like us wouldn't do so well if there were still supernovas going off left and right. There's a theory with decent evidence that at least one of the mass extinctions was caused by a supernova: https://www.space.com/supernova-caused-earth-mass-extinction...

That being said, I wasn't aware of how LIGO changed the understanding of how heavier elements are usually formed, guessing it changed the expected neutron star prevalence? Do you have any additional reading on that?

You are right about supernova hampering life evolution, but it's unclear how long the fireworks lasted. In my comment I argued that it is possible to have the conditions of life emerge much earlier than 13.5 billion years. Not that it necessarily happened.

Regarding the second point have a look at https://www.ligo.org/science/Publication-GW170817Kilonova/in... . That isn't my field of specialization, so I am not sure about recent publications. At the time though this was a big deal as kilonovas seem to be the primary source of heavy nuclei in the universe. That particular event crested between 1/100th to 1/1000th solar masses worth of heavy ( heavier than iron) nuclei. This is a greater rate than supernovas estimations.

> how LIGO changed the understanding of how heavier elements are usually formed, guessing it changed the expected neutron star prevalence?

It's not about the prevalence, but about the light curves observed during the event AT 2017gfo. They indicate significant heavy metal ejection but, what's interesting, also production.

> mergers of neutron stars contribute to rapid neutron capture (r-process) nucleosynthesis

These two articles cite the relevant papers:

https://en.wikipedia.org/wiki/GW170817#Scientific_importance

https://en.wikipedia.org/wiki/Nucleosynthesis#Neutron_star_c...

Very much a laymen also, however funnily enough I was listening to a bbc program called in our time, a couple of nights ago, where a similar topic was discussed one comment was that life is carbon based and for carbon to exist a star has to die, so yes therefore we are in the early stages. Will try to fin the episode….

> 13.5 billion years seems like the time required to create a star, have the star die and blow up, have all that material settle and create a new star, then the planets are formed, than enough time on one of those planets needs to pass for life to form, then complicated life.

Maybe for a main sequence star, but there other processes that involve nucleosynthesis.

That assumes that life as we know it is the only possible form of life.

Not necessarily, but look up the phosphorus problem.

  >all the atoms in our universe/galaxy/solar system with a mass up to that of iron are formed in the core of stars

Note that this is not, strictly speaking, true.

Roughly 90% of the helium atoms in the universe were created via Big Bang nucleosynthesis.

https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis

Iron is always spoken of as the dividing line, but I'd like to know whether iron is exactly on the line, on one side (which?), or it depends. IOW, does fusion of iron atoms release energy (hydrogen side of the line), absorb energy (uranium side of the line), neither, or either (depending on conditions)?

As I understand it, iron is the first element that absorbs energy under fusion, and therefore won't fuse further. Could be wrong, though.

It will happily fuse further. It just won't support the outside of a star against gravity, while doing it. So the star collapses, fuses lots more stuff even heavier than iron, and then explodes. Most of the iron and heavier stuff fuses into the core of a neutron star, the ultimate in energy-consuming fusion.

None of this is accurate.

Iron will not happily fuse further because this NEEDS energy and where would that energy come from?

"heavier than iron" elements are produced when a star explodes because that collapse produces enormous amounts of energy.

During the collapse, the outer edge of the star is accelerated to something like 20% of the speed of light, that is an ENORMOUS amount of energy slamming down on the core.

Lastly, neutron starts don't produce energy, they are the incompressible remnants of a dead star.

You answer your own question: the energy for further fusion, all the way to neutron degeneracy, is provided by gravitational collapse. The outer layers fusing provide energy for the explosion.

... which, it must be said, is probably more important than gravitation in overcoming nuclear charge repulsion.

My son has a masters in nuclear physics and i've always been curious as to why iron causes stars to explode.

He does an excellent job explaining things and put it to me like this.

Elements to the Left of Iron can undergo fusion and release energy, Elements to the right can undergo fission and release energy.

Iron IS the line because it needs energy to do either of these.

All elements want to find stability, and Iron is that Element because it needs energy for either fission or fusion.

So yes, Iron is the dividing line and this is what makes it so stable.

Edit: forgot to link the chart when referencing left or right..

http://www.splung.com/content/sid/5/page/benergy

Fusion to the left of Fe, fission to the right, here I am stuck in the middle with glu(ons)

(Yes I know it's technically mesons at the scale we're talking about but it doesn't rhyme so there)

Mesons should been called gluons, way stickier for sure.

The periodic table is pretty awesome. But I wonder if there's a layout that takes into account this fission/fusion division? Would it just be a line?

-- Yeah there are a few alternative designs, but nothing that seems to do the division. https://en.wikipedia.org/wiki/Alternative_periodic_tables

That's because the periodic table is essentially about chemistry (i.e. about electron orbitals), not about nuclear physics (i.e. the atom's nucleus). For example it doesn't talk much about isotopes, aside from usually reporting the average atomic mass.

My point is that there are other ways of organizing the same information to perhaps reveal unexpected connections. From the same link, a 'physicists periodic table' - https://en.wikipedia.org/wiki/Alternative_periodic_tables#Th...

And really, i guess everything is physics if you get specific enough.

Look at the binding energy curve: http://hyperphysics.phy-astr.gsu.edu/hbase/NucEne/nucbin.htm...

> all the atoms in our universe/galaxy/solar system with a mass up to that of iron are formed in the core of stars in stellar fusion.

all is a strong word

for example: the nuclear fusion experiment in the article, that would have produced a few atoms heaver that hydrogen

(not to mention all the nuclear bombs that had a fusion stage)

If I understand this right, I think some of the lighter than iron elements are also created in those exotic processes. But yes, unlike for the heavier-than-iron elements, the lighter ones are _also_ created in normal stellar fusion.

Heavier elements supposedly come from two neutron stars colliding because even a single star exploding isn't enough energy.

So think about two stars killing each other to make your jewelry.

we are all made of star stuff

or as I like to say to encourage myself that small things matter

"Stars are made of quarks"

What are quarks made of?

https://static.wikia.nocookie.net/memoryalpha/images/d/d9/Qu...

Star stuff sounds like some German element.

Exactly what I thought! I checked with google translate.

star stuff = sternzeug. stern stoff = star fabric

Stoff had more than one translation into English. One is cloth. Another refers to substances. Eg hydrogen is called Wasserstoff in German: water-stuff

See “waterstuff” in the Uncleftish Beholding:

https://www.ling.upenn.edu/~beatrice/110/docs/uncleftish_beh...

yet we all want to be

It is also interesting that the Milky Way will collide with Andromeda and then we will be invaded by zerg.