http://astronomynow.com/2015/12/09/g...eavy-elements/

Heavy elements present at the dawn of the Solar System were produced
by a nearby merger of two neutron stars, which unleashed a powerful
gamma-ray burst, according to astronomers at the Hebrew University of
Jerusalem.

Writing in the journal Nature Physics, Dr Kenta Hotokezaka, Professor
Tsvi Piran and Professor Michael Paul show how a significant quantity
of plutonium-244 found its way into the early Solar System following
the neutron star merger. None of this plutonium-244 remains in the
Solar System today, some four-and-a-half billion years later, but its
presence can be inferred. With a half-life of only 80 million years,
the plutonium-244 quickly decayed into more stable, daughter isotopes
of elements such as xeon, which can be found today in meteorites.

I remember reading some years back that there's a mystery about the
elements that make up the Solar System. Namely that it's possible that
two different types of supernovas were needed to seed our stellar nebula
when we were forming. That's because the types of elements we were
seeing couldn't come from only one type of supernova. Now it looks like
they're saying that not only did two different supernova happened in
close vicinity to each other, but then their neutron star remnants
spiralled into each other to form a black hole, which released still
more unusual elements! The chances of that happening are astronomical! I
guess it's a good thing that these are astronomical phenomena then.

Yousuf Khan