# Storing a Planet-sized Chunk of Metal Inside a Star

Would it be physically possible to "store" a planet-size or larger sum of metal, say gold or platinum, inside a star by letting it fall to the core?

Would it be possible to detect which stars had these treasures inside them?

(This is for a Sci-Fi project, but I'd like to root it in reality).

• The cost of energy required for both dumping and retrieving would be far higher than the value of the material, so why bother? – CuriousOne Oct 10 '14 at 1:20
• @CuriousOne Value can be quite a relative thing. How do you justify this? – Sam Washburn Oct 10 '14 at 2:04
• Economics of supply and demand. The only reason that gold and platinum are considered valuable is the low concentration of these materials near the surface of Earth. The production of gold for jewelry far outpaces its technical uses and platinum based catalysts are on their way out as chemists are learning to use low temperature reactions with synthetic catalysts. But as far as jewelry is concerned, how much gold and platinum does the average woman need? Certainly less than a small mountain of it... but that's what we are talking about when we are looking at planetary core quantities. – CuriousOne Oct 10 '14 at 4:00
• You might be interested in knowing that we have a site about worldbuilding. Your question could also fit there as well, expecially if you're looking for a way around the issues wth your premise or are willing to do some handwaiving. Which is not to say that posting your question here wasn't a good idea. I would suggest that you rewrite your question a bit to focus more on how to make what you want toa chieve work and post that version over at worldbuilding. – overactor Oct 10 '14 at 6:23

In astronomy parlance, the Sun has a "metal"$^{1}$ mass fraction of about $0.02$. A solar mass is $\sim2\times10^{30}\;\rm{kg}$, so the sun contains about $4\times10^{28}\;{\rm kg}$ of "metals". That's about $20$ times the mass of Jupiter. A lot of that metal mass will be ${\rm C}$ and ${\rm O}$ and other elements a chemist would call non-metals, but I think there should be enough ${\rm Fe}$, ${\rm Na}$, ${\rm Mg}$, etc. to make at least a small planet or large moon.

The elements you drop into the star would be roughly sorted into concentric spherical shells, ordered with the heaviest elements in the middle, given enough time. There is a serious risk, depending on the masses and elements involved, that whatever you drop in starts fusing and making different elements, or if the right thresholds are exceeded, that the entire thing explodes in a supernova.

The Sun is a fairly typical star, not especially massive or puny, metallicity not remarkably high or low. I already showed that the Sun has a fair bit of metal without anyone dropping in any extra, and there are massive metal rich stars out there that have more than a solar mass worth of metals inside occurring naturally. In fact, very nearly every atom in the Universe that is not hydrogen, helium or lithium was made inside a star (and anything heavier than iron was most likely made when a star exploded). Some metals get ejected in supernovae and in stellar winds, but a large fraction of the metal budget of the Universe is already locked up in stars.

It would be possible to detect the contents of a star, with a carefully measured spectrum of the atmosphere and sophisticated stellar modelling (the spectrum serves as a boundary condition for the model). It would be more difficult than what astronomers do today since part of what goes into the models is guided by how metals are transported naturally in the Universe; artificially moving stuff around throws a wrench in the gears, but it's plausible that a concerted effort by an intelligent civilisation could develop the necessary science.

Olin Lathrop and John Rennie have raised some concerns about retrieval. I agree that a wormhole is probably a bad idea. Perhaps your best bet for retrieval is to set some carefully calculated extra mass on a collision course, stand (way, way, way) back, let the star go BOOM, wait a thousand years or so for things to cool off, then harvest the metals out of the gas of the nebula. A $1000$ year old supernova remnant is still pretty harsh conditions; the Crab nebula (exploded in the $11^{\rm th}$ century) has a temperature of about $10,000\;{\rm K}$, but rather low density. I'd call it plausibly survivable by a suitably advanced spacecraft.

$^{1}$Astronomers call everything that is not ${\rm H}$ or ${\rm He}$ a "metal".

• Amazing. So is it possible to detect the amount of a certain metal element that exists in the core? How did we find that 0.02 number? – Sam Washburn Oct 9 '14 at 17:37
• @SamWashburn It's a combination of measuring the metals in the atmosphere using spectroscopy and coming up with well thought out models for the interior. In one sense we're "just guessing", but our guesses come with testable predictions, and the predictions are so far coming out pretty good... – Kyle Oman Oct 9 '14 at 17:38
• In an ordinary star, only the Hydrogen will fuse--the pressures and temperatures for helium fusion are much higher than those for hydrogen fusion, and this will not happen, for the most part, until the hydrogen in the core is exhausted. Of course, for anything heavier than iron, fusion will be endothermic, and will not happen spontaneously. – Jerry Schirmer Oct 9 '14 at 17:50
• I always thought that the spectrum of a star is mostly created by the "surface", and that the photons from within the star need a really long time to "travel" since they are constantly absorbed and reemitted. Won't that make the detection via spectrum infeasible (at least for within a certain time after dropping stuff into the star). – PlasmaHH Oct 9 '14 at 20:08
• @PlasmaHH as I said in my previous comment, the spectrum is of the atmosphere, which serves as a boundary condition for a model of the interior. We think the models are reasonably good since they've made some correct predictions, one of which is the neutrino flux from the Sun, which does come directly from the core, unlike the photons. Clarified the answer a bit anyway, thanks for the comment :) – Kyle Oman Oct 9 '14 at 21:53

"Storing" something implies the purpose is to put is somewhere safe so that it can eventually be retrieved. Heavy metals should eventually sink to the center of a star, but how are you going to retrieve it? Even in a science fiction context, it's hard to imagine a plausible means or retreiving a large pile of heavy metal from the center of a star. Therefore, I'll say no, it's not possible.

• My idea for retrieval was a well-placed wormhole. – Sam Washburn Oct 9 '14 at 17:08
• @SamWashburn: even assuming wormholes exist (they almost cetainly don't) putting one end inside the core of a star would be like uncorking a bottle containing plasma at 20 million degrees and 250 billion atmospheres. The result would make a hydrogen bomb look tame. – John Rennie Oct 9 '14 at 17:30
• @JohnRennie bah, if we have the technology to open an artificial wormhole to the core of the star I'm sure we can equip it with an annular pressure technobabulator to reduce the pressure and allow only the precious metal through. – Michael Oct 9 '14 at 18:40
• annular pressure technobabulator just needs to be said again. @SamWashburn should fit that in his book somewhere. ;) – paqogomez Oct 9 '14 at 20:18
• @Luaan: Yeah, I was thinking of a fairly large orbit, something like several planets out, but at right angles to the predominant planetary orbital plane. As you say, someone would be quite unlikely to stumble upon it if they didn't already know it was there and where to look. In our system, I'd have it at a distance from the sun between the orbits of Mars and Jupiter. – Olin Lathrop Oct 10 '14 at 12:59