# Does the Sun have an Iron-Nickle core? **URL:** \ **Category:** Factual Questions\ **Created:** [July 10, 2013, 7:04pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161 "2013-07-10T19:04:57Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 10, 2013, 7:04pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/1 "2013-07-10T19:04:57Z")
My (admittedly limited) understanding is that the Sun is a Population II star - it formed from the remnants of previous supernovas. Since the Earth has a metallic core, presumably, there was lots of metal in the dust/gas cloud that the Solar System was created from. So, if this is true, is there a lot of metal at the core of the Sun, and if not, why? ---
**Author:** ![Skald\_the\_Rhymer](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Skald\_the\_Rhymer](https://boards.straightdope.com/u/Skald_the_Rhymer)\ **Post date:** [July 10, 2013, 7:21pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/2 "2013-07-10T19:21:15Z")
> [@beowulff](#): > > My (admittedly limited) understanding is that the Sun is a Population II star - it formed from the remnants of previous supernovas. Since the Earth has a metallic core, presumably, there was lots of metal in the dust/gas cloud that the Solar System was created from. So, if this is true, is there a lot of metal at the core of the Sun, and if not, why? Sol is not a terrestrial planet. It’s a star. Currently it;s something like 90% hydrogen by number of atoms (according to the Encyclopedia Britannica), and most of the rest is helium. So no, it does not have an iron-nickel core. ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [July 10, 2013, 7:24pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/3 "2013-07-10T19:24:50Z")
The sun is so hot that there is no solid matter within. It is plasma. Hence, no nickel-iron accretion. There is, however, [plenty of metal in stars](https://en.wikipedia.org/wiki/Metallicity). ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [July 10, 2013, 7:34pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/4 "2013-07-10T19:34:26Z")
> [@Chimera](#): > > There is, however, [plenty of metal in stars](https://en.wikipedia.org/wiki/Metallicity). Note that “metal” in Stellar Chemistry means “anything of atomic number greater than two”, not just what we think of as metals. 🙂 ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [July 10, 2013, 8:00pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/5 "2013-07-10T20:00:14Z")
> [@beowulff](#): > > My (admittedly limited) understanding is that the Sun is a Population II star - it formed from the remnants of previous supernovas. Nitpick: Population I. Population II (and hypothetical Pop. III) stars are the metal-poor earlier generations. The populations were named in order of discovery, and only later was the connection to age established. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [July 10, 2013, 8:40pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/6 "2013-07-10T20:40:34Z")
It may end up with a carbon/oxygen core eventually, but for the moment, the core is predominantly hydrogen and helium. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 10, 2013, 8:45pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/7 "2013-07-10T20:45:46Z")
> [@Ponderoid](#): > > Nitpick: Population I. Population II (and hypothetical Pop. III) stars are the metal-poor earlier generations. The populations were named in order of discovery, and only later was the connection to age established. Huh. I’ve read that information many times and always missed that. :smack: OK, so, the Sun is Iron-poor. Why? The Earth is Iron-rich (35% iron, from some random site on the web). Where did all the Iron go when the Sun was forming? ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 10, 2013, 9:20pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/8 "2013-07-10T21:20:57Z")
> [@beowulff](#): > > OK, so, the Sun is Iron-poor. > Why? > The Earth is Iron-rich (35% iron, from some random site on the web). Where did all the Iron go when the Sun was forming? It’s not so much where the sun’s iron went - it’s where the Earth’s hydrogen went. I think the current planetary formation models say that basically the whole solar system formed out of a nebula with a composition similar to the sun’s. Heavier elements tended to clump together because gravity could hold them together even at relatively smaller sizes. You need to be big to hold onto gas. Once the sun started nuclear fusion, the solar wind stripped out all the extra gas, leaving some small terrestrial planets that were not able to hold onto the lighter gasses, and some gas giants that could. ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [July 10, 2013, 10:03pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/9 "2013-07-10T22:03:02Z")
> [@beowulff](#): > > The Earth is Iron-rich (35% iron, from some random site on the web). Where did all the Iron go when the Sun was forming? Could it have gotten split into lighter elements by the insane levels of energy? As I understand it, the sun actually recycles some of the helium it produces back into hydrogen because there’s too much energy for helium to remain stable. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [July 10, 2013, 10:03pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/10 "2013-07-10T22:03:51Z")
Side note: the sun has as much iron in it as 1,500 earths. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 10, 2013, 10:21pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/11 "2013-07-10T22:21:11Z")
> [@](#): > > Could it have gotten split into lighter elements by the insane levels of energy? As I understand it, the sun actually recycles some of the helium it produces back into hydrogen because there’s too much energy for helium to remain stable. Trace amounts, perhaps, but not enough to matter in any sense. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 10, 2013, 10:29pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/12 "2013-07-10T22:29:35Z")
> [@Pasta](#): > > Side note: the sun has as much iron in it as 1,500 earths. But, it’s 333,000 time more massive. So, it’s still very iron-poor. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [July 11, 2013, 2:48am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/13 "2013-07-11T02:48:39Z")
Really? I just got done teaching kids that medium sized stars can’t make elements past carbon, and nothing mentioned that there are heavier elements in there from the previous nebula. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [July 11, 2013, 3:55am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/14 "2013-07-11T03:55:32Z")
> [@beowulff](#): > > But, it’s 333,000 time more massive. So, it’s still very iron-poor. Yeah, I was just following on from **dstarfire** ’s point that the problem should be looked at the other way: Earth is light-element poor due to its small size and proximity to the sun. Of all the iron in the solar system, the vast majority of it ended up in the sun. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [July 11, 2013, 4:29am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/15 "2013-07-11T04:29:57Z")
> [@Cardinal](#): > > Really? I just got done teaching kids that medium sized stars can’t make elements past carbon, and nothing mentioned that there are heavier elements in there from the previous nebula. The heavier elements in Sol and its planets come from the previous star that nova’d. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [July 11, 2013, 8:39am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/16 "2013-07-11T08:39:07Z")
There is a big cloud of nebulous material (literally, material from a nebula, i.e supernova remnants) - mostly gaseous hydrogen, some helium, heavier solid elements in various proportions. Something acts to disturb the cloud (stellar encounter, nearby supernova shockwave) and adds some angular momentum so the cloud starts spinning somewhat. The things that get moved most by the disturbance are the light gaseous elements, so they compress a bit more, and start to accumulate under their own gravity - this is the protostar forming. As the central mass increases, there are various forces involved. Gravity pulls in - lighter gaseous elements move more to the center Angular momentum - solid masses (carbon, iron) tend not to due to rotational velocity Heat - from the protostar keeps volatiles in the central area gaseous, so only some heavier elements/molecules can condense near the star Radiation pressure from the protostar - this “blows out” lighter elements and gaseous molecules outside the area of gravitational attraction to cooler areas where they can condense. This gives the classic model of planetary system formation - light element sun, rocky planets, gas giants, oort cloud. Of course, we are now discovering that this model is not generally stable, and few systems retain this configuration over a planetary system lifetime. ---
**Author:** ![stanger](https://avatars.discourse-cdn.com/v4/letter/s/7ba0ec/32.png) [@stanger](https://boards.straightdope.com/u/stanger)\ **Post date:** [July 12, 2013, 11:48pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/17 "2013-07-12T23:48:09Z")
From what I have picked up over the last few years, when stars start winding down, the cores change to heavier elements over time as their fuel burns down. This may not happen to all suns, maybe not ours, but to the larger ones. The sun eventually gets to the point where it starts making iron, at which point it pretty much goes out. Apparently, once a start hits this stage, the process of elemental conversion halts. I was under the impression that when a stars core started turning to iron, the star dies very quickly, though I don’t know in astronomical terms if that means a matter of minutes of a few centuries. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [July 13, 2013, 5:07am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/18 "2013-07-13T05:07:43Z")
Is “nickle” American spelling now? ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [July 13, 2013, 6:10am UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/19 "2013-07-13T06:10:57Z")
> [@stanger](#): > > I was under the impression that when a stars core started turning to iron, the star dies very quickly, though I don’t know in astronomical terms if that means a matter of minutes of a few centuries. I read a wonderful tale of a supernova in Sci-Am many years ago. Iron is the first natural product of fusion that cannot be exothermically fused into something heavier (requires more energy to fuse than the reaction yields). Iron, IIRC, derives from silicon, which is the last progressive fusion reaction that produces net energy. Seems to me the article said that once a giant starts burning silicon, it has about one earth-day or so before the big plooey. Odd that there do not seem to be any “normal-sized” stars. We have dwarves and we have giants, nothing in between. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 13, 2013, 12:47pm UTC](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161/20 "2013-07-13T12:47:14Z")
The dwarfs (note: It’s always pluralized this way when talking about stars) _are_ the “normal-sized stars”. Giants are quite rare, and are only overrepresented in our data sets (such as, say, the set of stars visible to the naked eye) because they’re really easy to see. [Next page](https://boards.straightdope.com/t/does-the-sun-have-an-iron-nickle-core/663161.md?page=2)