Is there a link between a star's metallicity and the availability of chemical elements in its system?

Question

Considering aspects of interstellar trade for worldbuilding purposes, I'm researching what resources might be available in each star system.

The premise is that if one star system has an abundance of a particular resource that is rare, hard to obtain or unavailable at all in other star systems but is in high demand for whatever reason, this resource would be this star system's primary export commodity.

I'm abstaining from inventing fictional resources and materials and keeping to the real-world chemistry.

Gathering data, I have noticed that stars have varying metallicities. This has raised the question posed in the title.

I consider available only the elements on planets, moons, asteroids and comets and as particles floating in interplanetary space.

Answer 1

I think probably not if you are interested in particular elements but possibly yes, if you are interested in groups of elements that are formed from particular nucleosynthesis pathways.

Stars certainly do vary in terms of their metallicity and that mostly, but not always, reflects the abundances of the various elements in the gas from which they were formed. In the case of the Solar System, the photospheric abundances that are measured in the Sun also match very well the relative abundances that are found in meteorites. i.e. The solids have a composition that follows the composition of the gas.

How available these solids are will depend entirely on the details of the planetary system and so one can't generalise. Solid cores that are sourrounded by extensive envelopes of gas or icy fluids (like the giant planets in our Solar System) are not very available. If rocky planets have had a substantial period where they are molten, due to heat of formation or radioactivity, then there is differentiation whereby the heavier elements will sink to their centres. The smaller bodies however, like the meteorites discussed above, should contain whatever chemical peculiarities are present in the star, at least as far as the heavier elements are concerned.

So what peculiarities are there? Well there are all sorts of chemically peculiar stars that have photospheric abundance anomalies, sometimes manifested as very high abundances of one or two elements. However, these peculiarities are likely "skin deep", are caused by internal processes and don't reflect the initial bulk composition of the star and therefore are unlikely to be duplicated in any surrounding planetary system. Unless you are somehow able to "mine" the surface layers of the star, then that isn't much help (hence my query to your question).

A better bet is to focus on stars that may have been abnormally enriched by particular nucleosynthetic pathways in previous stellar generations. For example it may be that a star forming region is enriched by one or more kilonova explosions caused by merging neutron stars. This might inject an abnormally high amount of r-process elements like gold, platinum and lanthanides. The subsequently formed stars and their planetary systems might be expected to have a higher abundance of these elements. Whether they are available or not depends on where you try to find them.

The problem with this scheme is that individual kilonovae or supernovae probably don't make much of a mark in star formation that has taken place over the last many billions of years. That is because the interstellar medium is already enriched by hundreds of millions of such events in the first billion years or so of our Galaxy's existence. Thus when you do identify stars with big r-process element enhancements (e.g. Gull et al. 2021), they are old, generally metal-poor stars and thus have absolute r-process abundances that are still rather low. Nevertheless, if solid material and planets etc. can form around these stars then it could be that those solids are also r-process-rich and these planetary systems could be literal gold-mines.

The evidence on this is lacking, though. Giant planets probably are much rarer around metal-poor stars (e.g., Boley et al. 2021), but whether that is also true of the smaller bodies where you might want to mine your r-process elements is not well understood (e.g., see this article).

Answer 2

Yes, but with a lot of scatter.

The higher the metallicity of a star, the higher is the likelyhood that it hosts planets, and if it hosts planets that it hosts more of them.

E.g. see this graph obtained from exoplanet.eu. The higher the metallicity of the host stars, the more planets have been detected.

Our own solar system is good evidence that the elementary abundance in the Sun and its planets does not deviate too much from each other - and the differences can be explained by their different genesis and physical and chemical evolution from a more or less homogeneously mixed cloud of gas and dust (=anything solid). Looking much closer there are tiny differences which can be attributed to different parts of the proto-solar cloud.

This also is expected when looking at how stars and their planetary systems form: they are born from the same cloud of material which collapses in the center to the star. Doing so an accretion disc forms through which the protostar obtains more material - the protoplanetary disc. The difference in chemistry is now how volatile the materials are: the proto-star has enough gravity to hold every element, but the planets still have to grow, thus they start with heavy elements - and given the temperature gradient within the protoplanetary disc, the inner planets also have a relatively high component of high-temperature solids while the further out you go, the fraction of volatile elements including ices beyond the snow line increases.

See also these related questions here on SE and their answers which all touch the formation of our solar system and the element abundances and the last one a bit more generally the correlation between metallicity and planet abundance around stars Kepler observed.

• Composition of ice giants
• What is the definition of the "solar mixing ratio"?
• Why is the composition of the sun so distinct from that of earth?
• Are heavy elements equally distributed throughout the Solar System?
• Reason for a correlation between Hot Jupiters and higher metallicity in Kepler data

Answer 3

Yes! There is a relation between the metallicity and the chemical abundances of a particular element, not because of the main star but because of the Stellar nurseries (dark nebulae) the star was formed from. A star is given birth in a stellar nursery (a kind of nebula) wherein a large molecular cloud collapses under its gravity and attempts sort of a hydrostatic equilibrium which helps it to be stable and be a protostar (via the nebular hypothesis).

One important point needed is that these molecular clouds are basically the remnants of a previous supernova hence the name Supernova Remnants or SNRs, which via nucleosynthesis and neutron capture processes increases it's metallicity till iron, the first stars which started this and their primordial nebulae was not recycled and thus weren't SNRs, to do this were population III stars or 1st generation stars.

However once the formation of a protostar is started there is a torus shaped disk called the protoplanetary (circumstellar) disk which is just the remnants of the gas and dust which was not trapped inside, which contains all the metallicity of the previous nebulae (*Source) through which the star was formed so technically the metallicity of the planet is linked to the original stellar nursery but not fully through the star because in the new star nucleosynthesis happens whereas in planets it does not so for a particular point the metallicity of the star during the PMS (Pre-main-sequence), Protostar phase where no nucleosynthesis occurs is the same as the planet.

Also in red giants stars in the HR diagram where all the metallicity is diffused till the surface via convective currents, if a coronal mass injection occurs all the metals will be shot out into the interplanetary medium.