system
Given the following post, respond as if you're commenting on Reddit:
human
How do stars create extremely heavy elements after uranium?

I know  that supernovas can create extremely heavy elements (up to uranium as far as I know), but how are the elements after that formed?
gpt
Same process, just that Uranium 238 has a half-life of 4.5 billion years. Whereas the half-life of everything higher than that is much shorter. So in the time it takes to go from supernova to forming planets to us seeing it, those higher elements have long since decayed away to smaller more stable ones.

Otherwise we can form them in reactors by bombarding heavy atoms with neutrons or other particles. The smaller particles get absorbed to form a higher atom.

For example americium 241 is commonly found in smoke detectors. With a half life of 432 years it was long gone from the planet. But by bombarding U-238 with a neutron we get Pu-239. Then Pu-239 absorbs two neutrons to get Am-241.