https://www.centauri-dreams.org/

What to make of the star’s spectrum? It’s laced with oddball elements like europium, gadolinium, terbium and holmium. Moreover, while iron and nickel appear in low abundances, the stellar atmosphere shows the presence of short-lived ultra-heavy elements like actinium, plutonium, americium and einsteinium.

The latter were identified in 2008. Called actinides, these are elements with atomic numbers from 89 to 103 on the periodic table. They force the question of how radioactive elements with half-lives on the order of centuries or even decades could be there.

Stars form heavier elements in their cores during their lifetimes as a result of thermonuclear fusion reactions in their interiors. Elements heavier than iron are formed by neutron absorption during supernova explosions, their presence in the earth’s crust and in solar spectra is evidence of supernovae events that occurred BEFORE the solar system formed; these explosions enrich the interstellar medium with heavier elements that cannot be manufactured in normal thermonuclear fusion. Stars forming from this material therefore contain species which cannot be formed within the star’s core. Many of these heavier elements are radio-active, with relatively short half-lives. Older stars should not have any of this material left in them. Their presence there suggests they have been added to the stars, and that they are continuously being replenished.

Whether this is evidence of some as-yet unknown conventional physical process, or a deliberate seeding by an extra-terrestrial culture trying to advertise its presence, is the million dollar question.