Comment by somat | Hacker News Reader

Comment by somat | Hacker News Reader

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I went down an interesting rabbit hole recently, I was trying to figure how big the iron core of the sun was and the answers were surprisingly all over the place.

There is the no iron core/fractional percentage gang which bases their theory on the observed sun, but this conflicts with the common cloud theory of solar system origin, which is basically there was enough iron in the proto cloud to provide iron cores for most of the inner planets and you are telling that you think that most of this iron did not end up in the middle of the sun.

then at the far end of the spectrum is the crackpot "the solar system is a second generation(minimum) system, some star must have exploded to form the metals we see, the core of the sun is probably the stellar remnant of the first generation system and is mostly iron"

But really I wonder, all our observations of the sun are of the upper atmosphere, and more importantly the light emitted by the upper atmosphere, if earth was observed the same way you would conclude it was mainly made of nitrogen.

I recently realized it takes light over 4 seconds to cross the diameter of the sun. It seems absurd to conclude what's inside it based on light emitted at the surface. Other methods of deduction maybe, but not that.

The Sun is opaque to light in its interior. The light we see -and its absorption lines- is emitted in the photosphere, far from the core.

Our sun does not have an iron core. If it did, it would immediately collapse into a black hole.

When the sun burns all of the hydrogen in the core, it will then burn helium. The burning will end at carbon.

https://en.m.wikipedia.org/wiki/Carbon-burning_process

Silicon burns to iron, which becomes degenerate matter that cannot resist gravitational collapse.

> Our sun does not have an iron core. If it did, it would immediately collapse into a black hole.

Even if the sun were 100% iron, at its current mass it would not collapse into a black hole.

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

chasil is talking about a star that was able to form an iron core naturally through fusion, not a thought experiment of a ball of iron with the same mass as the current Sun.

This hypothetical is getting into "if my granny had wheels she'd be a wagon" territory.

I interpreted the original comment as if the Sun, with its current mass, had an iron core. A star with the mass of the Sun cannot have produced iron, so it would have had to have formed with an iron core. This is certainly ruled out by other data, of course.

Linking to Wikipedia is ridiculous here, considering we are discussing the current scientific debate and consensus. You just worded your contribution more forcibly.

There was a bunch of iron in the proto dust cloud that formed this solar system(i pick on iron because it is a nice infliction point past which you get no energy from fusion, but really include all of the middle stable elements here), as the dust cloud collapsed it formed an iron core in all the planets, and many asteroids. but no core in the sun, explain how that is possible.

really, I expect at minimum an earth sized iron core in the sun, it is probably much more.

The Earth has an iron core because iron separated into a separate chemical phase that was denser, and this denser phase percolated downward into the center.

The Earth does not have its iron core because individual iron atoms, being heavier, individually diffused downward into the core. Some heavy elements, like uranium, are actually highly concentrated in the continental crust, because chemically they partition into lower density phases.

In the Sun, with everything inside vaporized, there is and was no partitioning into distinct chemical phases of differing density. There is a chemical difference in the Sun's core, though: it is now enriched in helium and somewhat depleted in hydrogen because of nuclear fusion over billions of years. This process is gradually making the core denser and hotter, increasing the overall rate of fusion. The Sun is now 30% brighter than it was when it settled onto the main sequence.

Separation by mass of ions does occur in the surface layers of white dwarf stars; the conditions there are such that separation by diffusion can be significant. Some such stars have been seen with "metals" (elements heavier than helium) in their crusts; this has been interpreted as evidence of recent accretion of material from disrupted asteroids or planets.

What fraction of crustal uranium would you estimate was sourced from the "late veneer"?

Very little? The ratio of uranium to platinum in the crust is many orders of magnitude higher than in carbonaceous chondrites.

The sun's core is overwhelmingly composed of helium and hydrogen, with about 1% oxygen and about %1 everything else. At least according to the standard model, I don't know how much "wiggle room" there is in our understanding

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

At the edge of the core is about 70% hydrogen 28% helium with the helium fraction increasing up to 66% right at the center.

One thing I think you're missing is how overwhelmingly the cloud that formed the solar system was hydrogen and helium.

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

The gas cloud that formed the solar system is expected to have been 98% hydrogen and helium, 2% everything else. We don't see these ratios on rocky planets like earth because the gravity here isn't strong enough to hold the hydrogen and helium, so mostly it escaped and we have a wildly non-representative sample of elements left.

There is enough iron in the Sun for an iron core.

Nevertheless, the standard model of the Sun supposes that, because of the very high temperature, the interior of the Sun remains mixed well enough so that the heavy elements like iron cannot segregate to form a distinct core, but only, as you have mentioned for helium, the concentration of heavy elements is somewhat higher in the center than at the surface.

However the standard model of the Sun is not very certain, because the behavior of matter at extremely high pressures and temperatures is not known well enough.

The Sun has iron in it. There are at least 500 earth-masses worth of iron in the Sun. But it's distributed all throughout the Sun and not collected into the core. Do you have a PhD in solar plasma computational fluid dynamics modeling? No?? Then maybe pay attention to what mainstream astrophysics people say about the Sun's core.

<https://news.ycombinator.com/item?id=39696275>

Please leave credentialism out of it.

IANAA

If there was an iron core, it would vaporize in the center of the sun because it's extremely hot there.

A few years ago, someone measured the energy of the neutrinos produced by the fusion in the center of the Sun [1].

[1] perhaps there are some details in https://en.wikipedia.org/wiki/Solar_neutrino

An iron core is actually the precursor for either a black hole or a neutron star.

There is an exothermic fusion chain of elements that are burned in stars, the last stage of which is silicon, that ends with iron.

https://en.m.wikipedia.org/wiki/Silicon-burning_process

At iron, no further exothermic fusion is possible, so the core is no longer able to resist the pressure of collapse.

The iron atomic nuclei themselves break down, the protons combine with electrons to form neutrons where they are able, and if the total mass is below the Tolman–Oppenheimer–Volkoff, then neutron degeneracy pressure is able to stop the collapse, otherwise a black hole forms.

https://en.m.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E...

A star needs to be 8 solar masses for this to happen. Our sun ends at carbon.

But it the star is't a gas core made of Iron mixed with Hydrogen, Helium and other intermediate stuff, or it's a solid metallic almost pure Iron like on Earth? (IANAG neither)

For a sufficiently massive star, all of the hydrogen, helium, carbon, neon, oxygen, and silicon in the core are gone after silicon burning is complete.

They were consumed as fuel to maintain the outward pressure of the core.

> A star needs to be 8 solar masses for this to happen. Our sun ends at carbon.

Wikipedia says the TOV limit is ~3 solar masses?

I know, that this doesn't help really, but in plasma physics as well as when dealing with degenerate matter and such 8 and 3 are the same number. Most of the time a scientist in these fields is happy to get the order of magnitude right! ;P

"Assume Pi is 1" is such a great conversation starter!

https://www.xkcd.com/2205/

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