How Heavy Elements are Produced

An artist’s illustration of merging neutron stars.

Credit: Robin Dienel; Carnegie Institution for Science

Monday's (Oct. 16) historic announcement of the detection of gravitational waves produced by two colliding neutron stars has provided explanation as to where in the elements heavier than iron are synthesized.

Until astrophysicists were able to observe the merger of two neutron stars, there only had theories about how heavy elements like gold, platinum and lead are created in the cosmos.

Neutron stars are the corpses of massive stars whose cores collapsed in supernova explosions. While they’re not that big, they’re incredibly dense, packing a sun’s worth of mass into the size of a city. A teaspoon of neutron-star stuff weighs around a billion or so tons.

Neutron stars contain some of the building blocks of atomic nuclei. If these neutrons are somehow released from a neutron star, they undergo reactions that allow them to stick together, creating elements heavier than iron. All of the post-iron elements are formed in these supernova explosions. So much energy is released during a supernova explosion that the freed energy and copious free neutrons streaming from the collapsing core drive massive fusion reactions, past the formation of iron.

Researchers are witnessing a distant heavy-element factory synthesizing "maybe hundreds of Earth masses' [worth] of gold and … maybe 500 Earth masses' worth of platinum," astrophysicist Daniel Kasen said in a new video.

Related reading: New Era of Astronomy; The Collision of Two Neutron Stars; Gold from Neutron Star Crashes