The radioactive nuclei and in the Cosmos and in the solar system

Abstract

The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging, as they have biases in time and space as well as different sensitivities related to the various astronomical methods. Here, we describe in detail the astrophysical and nuclear-physical processes involved in creating two radioactive isotopes useful in such studies, $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ . Due to their radioactive lifetime of the order of a million years, these isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of $^{26}\mathrm{Al}$ and $^{60}\mathrm{Fe}$ , the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. This allows us to connect the theoretical astrophysical aspects to the variety of astronomical messengers presented here, from stardust and cosmic-ray composition measurements, through observation of $\gamma$ rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of $^{26}\mathrm{Al}$ to $^{60}\mathrm{Fe}$ eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution. This review paper has emerged from an ISSI-BJ Team project in 2017–2019, bringing together nuclear physicists, astronomers, and astrophysicists in this inter-disciplinary discussion.

Spectra of Cosmic-Ray Sodium and Aluminum and Unexpected Aluminum Excess

“…Potential sources include AGB stars, novae, core-collapse supernovae, and Wolf-Rayet (W-R) star winds (Prantzos & Diehl 1996;Diehl et al 2006). A very recent review of the nucleosynthesis reactions involved in the production and destruction of 26 Al and 60 Fe and characteristics of the stellar sites of their nucleosynthesis can be found in Diehl et al (2021).…”

Chemical evolution of $^{26}$Al and $^{60}$Fe in the Milky Way

“…We then assume 10 4 outbursts in total during the life of a nova system. a ratio in the range 0.2 − 0.4: as stated by Diehl et al (2021), this flux ratio can be converted into a mass ratio that lies in the range 0.7 − 1.5M . Therefore, by assuming that the best 26 Al mass observation is 2 M , 60 Fe mass should lie in the range 1.4 − 3.0 M .…”

The 26Al Production of the ν e -process in the Explosion of Massive Stars

“…But they assumed relatively large energies for the supernova neutrinos that are not supported by current simulation results. The contribution of the neutrino process is significantly reduced to about 10% when the lower neutrino energies are adopted (Sieverding et al 2018;Diehl et al 2021). So the previous studies have suggested that about 0.2 M e of 26 Al is contributed by the neutrino process.…”

“…In the early 2000s, the present total mass of 26 Al in the Milky Way was determined to be 2.8 ± 0.8 M e from γ-ray observations (Diehl et al 2006). Now, the observations constrain it to fall between 1.7 and 3.5 M e , with a best estimate of 2 M e (Diehl et al 2021). Timmes et al (1995a) have estimated that the 26 Al yield can be increased by 40% with the neutrino process.…”