Periodic Reporting for period 3 - RADIOSTAR (Radioactivities from Stars to Solar Systems)
Periodo di rendicontazione: 2020-09-01 al 2022-02-28
To answer the first question of the production of radioactive nuclei in stellar objects we have focused on many radioactive nuclei and the large variety of their possible stellar origins. We have calculated predictions for the production of aluminium-26 in the winds of massive stars (those roughly 10 times more massive than the Sun) also considering that most of these stars have a stellar companion of similar mass with which they interact. We are expanding these predictions to include the effect of stellar binarity also on other radioactive nuclei produced by winds, such as chlorine-36 and calcium-41. We have analysed the slow neutron-capture process that occur in giant stars (of initial mass a few times larger than the Sun), which are responsible for producing short-lived radioactive nuclei such as palladium-107 and hafnium-182, and established that stellar rotation, one of the major uncertainty of such models so far, should not have a major impact on the production of these nuclei. We have also considered the production of short-lived radioactive nuclei belonging to very heavy elements, such as curium-247, in rapid neutron-capture process sites (such as neutron star and black hole mergers) to identify the time when the last of such events contributed to the matter that formed the Solar System. Core-collapse supernovae, the final phases of the lives of massive star, also produce a large variety of radioactive nuclei. We are considering the production of fifteen such nuclei in these explosions using models that explore some of the many related uncertainties.
On the second question of the evolution of radioactive nuclei in the interstellar medium, we have published the first open-source computational code that follows the evolution of the abundances of the chemical elements in the galaxy including radioactive nuclei. This has allowed us to evaluate quantitatively and with error bars, the effect of galactic evolution and its uncertainties on isotopic ratios of radioactive to stable nuclei, the form in which the meteoritic data we compare our predictions to are obtained. We then moved onto considering that in the Galactic interstellar medium abundances can be heterogeneous, i.e. not perfectly mixed. This is particularly crucial in the case of radioactive nuclei because their decay time can be similar to the interval time between different injections from their stellar production sources into each specific location of the Galaxy where the Sun may have been born. We have developed a statistical method to evaluate quantitatively the effect of such heterogeneities and have started applying it to ratios of radioactive to stable nuclei, as well as of radioactive to radioactive nuclei. With this method we can evaluate not only one value for the absolute timescales related to the birth of the Sun, but also their error bars.