Viewing a single comment thread. View all comments

Mord42 t1_je1h4dp wrote

Reply to comment by AuDHDiego in Is NaCl relatively common in the galaxy/universe? by PHealthy

Yes! The creation of those elements take energy instead of releasing it.

53

AuDHDiego t1_je1hc6t wrote

Thank you! It's fascinating that we have any kind of nontrivial amounts of those elements at all in our grasp, considering their sources.

41

Walmsley7 t1_je1j43m wrote

Somebody may correct me if I’m wrong, but it helps that the stars that go supernovae have comparatively short life spans, so there have been several more “generations” of them. If I recall, the life span of those stars is measured in the millions of years, versus our sun which is projected to have a 10 billion total life span (and is about 4.5 billion years into it).

Edit: and versus the estimated ~14 billion year age of the universe.

34

forte2718 t1_je1pe8m wrote

You're somewhat correct — there are basically two known generations of stars, and a third hypothesized one.

The very first generation of stars would have lasted millions to tens of millions of years, were very metal-poor (being composed almost exclusively of hydrogen and helium left over from the big bang) and would almost all have gone supernova early on. None are still around today, and there is only scant evidence that they existed at all. Obtaining better evidence for this first generation of stars is one of the primary missions of the James Webb Space Telescope.

The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars. These were lower in mass on average and lasted much longer, hundreds of millions to billions of years.

Our Sun is a third generation star, which was likely formed from the compression of gas by second-generation stars going supernova. Third-generation stars like our Sun are much lower mass and higher metallicity, and have much longer lives on average.

All that being said, we would have obtained a mix of many elements because our Sun (and most second- and third-generation stars) and solar system were almost certainly formed out of gas clouds that had materials from numerous other exploded stars from both the current and previous generation. The second generation of stars was a lot more diverse than the first generation, and the third generation even moreso, so the diversity of elements that we seen in our solar system today comes from many different kinds of exploded stars in the two most recent generations.

Hope that helps!

27

Seicair t1_je2cmmp wrote

> The second generation of stars that formed had a middling metallicity, as they formed from material that included the higher-mass elements formed from the first generation of stars.

I’d like to point out for any chemistry enthusiasts not well versed in astronomy. In astronomy, it’s hydrogen, helium, or metal.

15

Beer_in_an_esky t1_je2vjad wrote

Astronomy, the field where Oxygen is a metal, and four orders of magnitude can be a rounding error. Love it.

13

SkoomaDentist t1_je2utiy wrote

Out of curiosity, why this divide? Is it just because hydrogen and helium constitute such large part of all matter that it makes no sense to divide the tiny remaining part further?

8

D180 t1_je4o60e wrote

That's the most important part I think, hydrogen and helium make up 98% of the universe as they were produced immediately after the big bang, all other elements matter much less.

There's also the fact that the chemical behaviour of an element does not matter much at the temperatures encountered in stars - the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together. If you heat up iron to 3000°C it stops being a metal and just behaves like any other dense, hot gas. But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures (for example, they rise to the surface of a star)

5

Seicair t1_je691wn wrote

> the properties we expect of a metal, for example, actually depend on the atoms being cool enough to stick together.[...] But since hydrogen and helium are so much lighter than other elements they will still have different behaviour at such temperatures

Hey, that makes sense, thanks for the explanation. I've kinda wondered why they use the terminology myself since I learned it. My specialty is organic chemistry.

1

GnarlyNarwhalNoms t1_je1q363 wrote

Yes, the luminousity of a star (which is a direct consequence of "units of matter fused per second") goes up as greater than the cube of mass, about M^(3.5). That means that even though they contain a lot more fuel, they burn through it far more quickly. So for example, a star with two solar masses has roughly twice as much fuel* as the sun, but it burns around 13 times as fast, so its lifespan is less than one sixth of the sun's, or maybe around 1.5 billion years**

So if you plug in a star with, say, 20 solar masses, all of a sudden, you're looking at a lifespan of a small fraction of a billion years.

* It gets a bit more complicated in that large and medium stars have a radiative zone at the core (high pressure supressing convection) underneath a convective zone at the surface. Small stars, smaller than the sun, are entirely convective, meaning that they can use the fuel from the entire stellar mass. Large stars have smaller convective zones which don't interface with the core, meaning that they can run out of fuel even if there's a substantial amount of hydrogen in the upper layers of the star. This is why using mass to calculate star lifetimes isn't as simple as using the entire star's mass to look at how much fuel will be fused. This is also why red dwarf stars have exceedingly long lifespans.

**These are highly handwavey numbers, don't check me on it, but you get the gist.

13

polaarbear t1_je1pcmi wrote

This is only true for Type II supernova. Type Ia supernova occur when a white dwarf (created in the death of a star like our sun) siphons enough mass of a companion star.

11

starlevel01 t1_je1qdhd wrote

> It's fascinating that we have any kind of nontrivial amounts of those elements at all in our grasp, considering their sources.

It's easier to think of it as an extremely large number (number of stars) multiplied by an extremely small number (probability of producing those elements) which rounds out to a reasonably-sized number.

12

Aethelric t1_je2lle8 wrote

The takeaway is not that the amounts available are nontrivial; rather, it's that we are trivial.

4

AuDHDiego t1_je2pplj wrote

Nothing is more humbling and numinous than the universe that stares us in the face

2

PatrickKieliszek t1_je1s5yi wrote

There are actually some exothermic reactions that produce elements more massive than iron.

However, these are usually very short lived in the time immediately before supernovae and are limited by photodisintegration. They don't meaningfully contribute to the amount of heavier elements (Which are primarily produced during nova).

9

Mord42 t1_je33pck wrote

That's interesting! Thanks for the information.

2