Back in 2017, scientists theorized that elements heavier than iron- such as gold- came to be following a collision between two neutron stars. But now, a new analysis has found that neutron star collisions do not happen nearly frequently enough to produce the number of heavy elements we see in the Milky Way galaxy today.
"Neutron star mergers did not produce enough heavy elements in the early life of the Universe, and they still don't now, 14 billion years later," says Amanda Karakas, an astrophysicist at Monash University in Australia.
"The Universe didn't make them fast enough to account for their presence in very ancient stars, and, overall, there are simply not enough collisions going on to account for the abundance of these elements around today."
During the early Universe, the first stars formed as gravity pulled together clumps of hydrogen and helium- the most abundant elements in the Universe. Over time, these elements fused into heavier and heavier particles until iron was produced.
While iron can fuse into heavier metals, it requires huge amounts of energy to do so. As such, the core of most planets, including our own, consist of iron.
To create elements heavier than iron, including gold, silver, and uranium, a rapid neutron-capture process, or r-process, is needed. One place where this can occur is in energetic explosions such as neutron star collisions. But this is not the only place.
Researchers now hypothesize that a type of supernova, known as magnetorotational supernovae, can also cause iron to fuse. Occuring when the core of a massive, fast-spinning star with a strong magnetic field collapses, they say that even if a small number of supernovae stars between 25 and 50 solar masses are magnetorotational, the discrepency in heavy metal quantities in the Milky Way could be accounted for.
While the researchers' models seemed to match this general theory, they note that their calculations also predicted more silver than observed and less gold. Whether this is a problem with calculations or fundamental theory, however, is yet to be understood.