An international research team recently developed a new copper-57 proton capture reaction rate for the extreme astrophysical environment at neutron star surfaces. The new reaction rate alters some of the most critical nucleosynthesis pathways in Type-I X-ray bursts, according to the researchers. The study was conducted by researchers from the Chinese Academy of Sciences’ Institute of Modern Physics, Monash University, the Centre d’EtudesNucléaires de Bordeaux-Gradignan, the Joint-Institute for Nuclear Astrophysics, and RIKEN and was published in The Astrophysical Journal.
Since the discovery of the first Type-I X-ray burst in the last century, astrophysicists have been eager to learn more about the physics that drives these bursts. Understanding their energy generation, the composition of burst ashes left on the neutron star surface, and possibly even their contribution to the formation of some of the universe’s rarest chemical elements are all part of this.
In order to build accurate models of these bursts, scientists must know the nuclear reaction rates of the key nuclides in addition to the macroscopic astrophysical conditions. They can model the chemical element syntheses using their detailed knowledge of the nuclear reaction path.
Previous research indicates that the copper-57 proton capture reaction is the fifth most influential reaction influencing the periodic thermonuclear burst of the X-ray source GS 1826-24.
In this study, the researchers discovered a new proton capture reaction rate of copper-57 that is only 20% of the previous rate. They successfully reproduced a set of theoretical X-ray burst light curves that closely match the observed light curves of the GS 1826-24 X-ray source using a cutting-edge Type-I X-ray burst simulation model (KEPLER code).
They discovered that the new copper-57 proton capture reaction rate significantly alters the burst ash composition. The burst ash composition is critical to the studies of superbursts, which burn these ashes, and neutron star cooling.
These findings aid in better constraining the equation of state of nuclear matter under extreme conditions inside neutron stars, which is essential for understanding gravitational waves from binary neutron star mergers and their gamma-ray burst counterparts in the multi-messenger era.