Some of the heaviest elements in the universe can only form in the cataclysmic collision between two neutron stars. These events, confirmed by observations only recently thanks to gravitational waves, end up “polluting” interstellar gas with elements like gold and uranium. And researchers suspect one such collision might have happened nearby, just before the Solar System formed.
About 0.3 percent of the Earth’s heaviest elements might have formed in such an explosion. The findings are reported in the journal Nature. The team estimated that this neutron star collision could have happened 4.6 billion years ago, that’s just 100 million years before the formation of our planet.
The key piece of evidence in this research is the composition of meteorites, many of which have remained unchanged since the formation of the Solar System. Neutron star collisions produce certain radioactive elements that decay over shorter timescales than 100 million years, but the elements they turn into remain trapped inside meteorites to this day. Certain isotopes (the same elements but with a different number of neutrons) have quite the decay signature and this gave the researchers a lot of information.
"Meteorites forged in the early Solar System carry the traces of radioactive isotopes," lead author Dr Imre Bartos, from the University of Florida, said in a statement.
"As these isotopes decay they act as clocks that can be used to reconstruct the time they were created," added co-author Dr Szabolcs Marka at Columbia University.
The team compared the abundances of elements in the actinide series (such as thorium, uranium, and plutonium, among others) in the meteorites with numerical simulations of the Milky Way and assessed how quickly elements from a neutron star merger can spread before decaying. Armed with that they estimated that the catastrophic collision must have happened no further than 1,000 light-years from the gas cloud that then birthed the Solar System.
"If a comparable event happened today at a similar distance from the Solar System, the ensuing radiation could outshine the entire night sky," Marka added.
Neutron star collisions are still mysterious events, mostly because neutron stars remain complex and difficult to study. The strides we have made recently thanks to gravitational wave observations have provided us with important new insights and could confirm if one of these events has happened right on our doorstep.