Half of naturally occurring plutonium on Earth might be from single neutron star merger.
Ars Technica said:We are all, as Carl Sagan said, star-dust. You might think that since most stars are pretty much the same, all star-dust is equal. But we have evidence that some star-dust is more equal than others. Yes, some elements seem to have a very special origin: neutron star mergers.
Most stars are pretty much all hydrogen. Near their center, fusion busily turns hydrogen into helium. Eventually, that hydrogen will run out and, like a pub that runs out of beer, the real destruction begins. The star starts turning helium into heavier elements at an increasingly feverish rate. The end, no matter how hot and heavy the star, comes when the star’s core is made of iron.
Up to iron, the process of fusion releases more energy than it consumes. But after iron, fusion consumes more energy than it releases, which essentially shuts the star down. Once this was understood, scientists were left wondering where the remaining 80 odd elements that are heavier than iron came from.
Bring on the neutron stars
Heavier stars end their life in a supernova—a violent explosion. These explosions can create many of the elements heavier than iron. However, a supernova will still only get us as far along the periodic table as molybdenum, leaving about 40 elements unexplained.
Then, a neutron star merger was observed, first via gravitational waves and later with various other hardware. It seemed that the merger produced the right conditions to create the remaining elements via a process called rapid neutron capture.
Imagine an iron atom sitting around minding its own business. Iron has 26 protons—the number of protons determines the element—and 30 neutrons, which act to glue the protons into the nucleus. Suddenly, thanks to a heavy neutron bombardment, the iron nucleus starts accumulating neutrons at a rapid rate. When the iron nucleus hits 32 neutrons, one of the neutrons emits an electron to turn into a proton. That turns the ion nucleus into a cobalt nucleus.
The capture and decay process can continue to encompass all the naturally occurring elements. But it only happens if there's a large source of neutrons to bombard the atom, which a neutron star merger provides. We've only observed one neutron star merger at this point, though, which leaves things a bit uncertain.
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