Background image is courtesy of Dark Energy Survey/Fermilab. Foreground image is courtesy of Alexander Ji, Anna Frebel, Anirudh Chiti, and Josh Simon

The lightest few elements in the periodic table formed minutes after the Big Bang. Heavier chemical elements are created by stars, either from nuclear fusion in their interiors or in catastrophic explosions. However, scientists have disagreed for nearly 60 years about how the heaviest elements, such as gold and lead, are manufactured. New observations of a tiny galaxy discovered last year show that these heavy elements are likely left over from rare collisions between two neutron stars.



The new galaxy, called Reticulum II because of its location in the southern constellation Reticulum, commonly known as The Net, is one of the smallest and closest known to us. Its proximity made it a tempting target for a team of astronomers, including the Carnegie Institution for Science’s Josh Simon, who have been studying the chemical content of nearby galaxies.



“Reticulum II has more stars bright enough for chemical studies than any other ultra-faint dwarf galaxy found so far,” Simon said.



Such ultra-faint galaxies are relics from the era when the universe’s first stars were born. They orbit our Milky Way Galaxy, and their chemical simplicity can help astronomers understand the history of stellar processes dating back to the ancient universe, including element formation.



Many elements are formed by nuclear fusion, in which two atomic nuclei fuse together and release energy, creating a different, heavier atom. But elements heavier than zinc are made by a process called neutron capture, during which an existing element acquires additional neutrons one at a time that then “decay” into protons, changing the makeup of the atom into a new element.



Neutrons can be captured slowly over long periods of time inside the star or in a matter of seconds when a catastrophic event causes a burst of neutrons to bombard an area. Different types of elements are created by each method.

