Understanding how the heavy elements came into being in the universe presents one of the greatest challenges in nuclear physics and astrophysics.  For some time we have known that elements beyond iron on the periodic table must have been made through neutron-induced reactions, but the environments where they are made and what they can tell us about this history of our galaxy remain a mystery.

Carbon is produced in stars mainly via the triple-alpha process where three helium nuclei fuse to form an excited state of carbon-12 known as the Hoyle state. This is a nuclear resonance (an excited form of a nucleus) that has properties that guide the rate that the triple alpha process takes place. Primarily, the key property is how often the Hoyle state is able to lose energy and end up in the ground state of carbon-12 – known as the radiative width.

Gamma rays from nuclear lines are the most-direct astronomical messenger for the occurrence of nuclear reactions in cosmic sites, next to neutrinos.

Characteristic lines from radioactive decays have been measured with space-borne telescopes, most-recently with ESA’s INTEGRAL mission, for the isotopes 56Ni, 57Ni, 44Ti, 26Al, and 60Fe.