This wikipedia article talks about how elements heavier than iron generally, and actinides (uranium etc) specifically are formed during supernova and also there is a mention that some/more/most(?) are formed during stellar remnant mergers.
What I’m curious about and haven’t found an answer to is this; how much is formed during these events? For example, how much uranium is formed? Is there a way to know or to estimate with a good degree of confidence how much is formed? Can we look at the Crab Nebula and say, “we estimate that x number of tonnes of plutonium was created during this supernova event using (a formula)”?
For all elements combined, we are talking from hundreds to thousands of Earth masses. So for any particular element, think in the range of 1,000,000,000,000,000,000,000 tons, give or take a few zeros.
I guess the question is a bit harder. For lighter elements we have good estimates about the relative productivities of the different nucleogenisis processes, which rather nicely fitted observation. Which was a big win. But for merging neutron stars I would guess the processes are a lot harder to model and get numbers for. Where harder is a somewhat arbitrary metric up to and including infeasible.
The conditions under which heavy elements are created are so extreme as to defy comprehension, and the range of physics so wild that I sort of doubt any sort of sensible quantitative analysis could be done. Then again, maybe it is something as simple as looking at the stabilities of the entire mess of possible outcomes and modelling it as some sort of annealing soup. (So well out of my depth here that I can’t even see the surface.)
I wonder what form the material is in? I’m imagining a gas that eventually condenses out to a fine dust of all these different elements mixed together?
Or is it released in something like stones? Chunks? Asteroids? All of the above?
If future humans sent a robot to harvest these heavy metals, what would it actually be picking up?
Interesting question. I don’t know if any astrophysicists are reading this, but I would love to hear their input.
I’ve only found two quantitative estimates in a few minutes googling, but these might give some idea of the scale of production. Supernova Ia events produce about a stellar mass of iron, which contributes to the store of planetary material in the galaxy (according to wikipedia); iron is a very common element, and 64% of all iron in the galaxy is produced in this way according to the chart posted in Mijin’s post above.
The amount of elements produced by various processes is much smaller than this, but the only quantitative figure I’ve found is that a recent neutron star collision produced gold ‘several times the mass of the Earth’. Since many of the other heavy elements are overwhelmingly produced by the same process (according to current theories), we can estimate the amount of uranium produced in a similar explosion.
I’m estimating from this graph in wikipedia that gold is about 10 times as abundant as uranium in the universe, so each neutron star makes ‘several tenths’ of an Earth mass of uranium. Maybe a bit more than a Mars-mass.
We don’t know enough about the behavior of neutron star material to be able to answer this question by modeling, for events involving neutron stars. Anything we know about the proportions produced would be from working backwards from the proportions we currently see of the various elements, and what we know of the various other processes.
For that matter, the processes that don’t involve neutron stars have a lot of unknowns in the modeling, too.
Indeed. supernova 1987A didnt show an increase in “heavier than iron” atoms… This suggested the r process matter was ejected outward, and remains concentrated.
I had read, eg Stephen Hawking, saying the “heavier than iron” elements in the earth suggested that earth matter had been through seven supernova events … but that seems to be in doubt with the concentration of r process material ejected from the supernova 1987a .
The r-process mentioned above is fairly “simple” to calculate given known beta decay rates and fission fragment distributions, measured terrestrially or filled in from nuclear theory. Calculations based on the r-process that match the relative isotopic abundances in the sun reasonably well (for astrophysics) have been around for nearly fifty years. These calculations are, of course, even better today.
The big questions for neutron star mergers, then, are (1) how much of this r-process material is ejected either initially or through follow-on processes (neutrino “wind”, black hole accretion disk ejecta), and (2) are such mergers common enough to provide the overall absolute abundances seen.
Simulations of the first part are not too bad (again, for astrophysics), with a factor of 10 or so spread in models. The second part has historically been much harder to pin down, leading to lots of uncertainty as to whether compact mergers are the dominant source of heavy elements or whether supernovae, say, provide substantial r-process production to account for these.
Exciting developments recently are that:
Gravitational wave detectors (e.g., LIGO/Virgo) have observed neutron star mergers, and
One of these violent events was successfully observed in a multi-messenger way. Lots of instruments using various EM bands were focused in on the event.
The above measurements – while still few in number – provide some concrete data on merger rates and the quantity of r-process ejecta from mergers. Turns out that mergers very well could explain basically all of the heavy element production, with no need for other significant sources.
If he said that, he was basing it on work done by others: That’s far from his area of expertise. And figures like that are likely to be constantly revised.
