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Context.Although current observations indicate that there are two distinct sequences of disk stars in the [α/M] versus [M/H] parameter space, further complexity is evident in the chemical makeup of the Milky Way and consequently suggests a complicated evolutionary history. Aims.We developed two-infall galactic chemical evolution (GCE) models consistent with the Galactic chemical map. Methods.We obtained new GCE models simulating the chemical evolution of the Milky Way, as constrained by a golden sample of 394 000 stellar abundances of the Milky Way Mapper survey from data release 19 of SDSS-V. The separation between the chemical thin and thick disks was defined using [Mg/M]. We used the chemical evolution environmentOMEGA+combined with Levenberg-Marquardt (LM) and bootstrapping algorithms for the optimization and error estimation. We simulated the entire Galactic disk and considered six galactocentric regions, allowing for a more detailed analysis of the formation of the inner, middle, and outer Galaxy. We investigated the evolution ofα, odd-Z, and iron-peak elements, covering 15 species altogether. Results.The chemical thin and thick disks are separated by Mg observations, which the otherα-elements show similar trends with, while odd-Z species demonstrate different patterns as functions of metallicity. In the inner Galactic disk regions, the locus of the low-Mg sequence is gradually shifted toward higher metallicity, while the high-Mg phase is less populated. The best-fit GCE models show a well-defined peak in the rate of the infalling matter as a function of the Galactic age, confirming a merger event about 10 Gyr ago. We show that the timescale of gas accretion, the exact time of the second infall and the ratio between the surface mass densities associated with the second infall event and the formation event vary with the distance from the Galactic center. According to the models, the disk was assembled within a timescale of (0.32±0.02) Gyr during a primary formation phase, followed by an increasing accretion rate over a (0.55±0.06) Gyr-timescale and a relaxation phase that lasted (2.86±0.70) Gyr, with a second peak seen for the infall rate at (4.13±0.19) Gyr. Conclusions.Our best Galaxy evolution models are consistent with an inside-out formation scenario of the Milky Way disk and in agreement with the findings of recent chemodynamical simulations. 

Radioactive nuclei are the key to understanding the circumstances of the birth of our Sun because meteoritic analysis has proven that many of them were present at that time. Their origin, however, has been so far elusive. The ERC-CoG-2016 RADIOSTAR project is dedicated to investigating the production of radioactive nuclei by nuclear reactions inside stars, their evolution in the Milky Way Galaxy, and their presence in molecular clouds. So far, we have discovered that: (i) radioactive nuclei produced by slow (107Pd and 182Hf) and rapid (129I and 247Cm) neutron captures originated from stellar sources —asymptotic giant branch (AGB) stars and compact binary mergers, respectively—within the galactic environment that predated the formation of the molecular cloud where the Sun was born; (ii) the time that elapsed from the birth of the cloud to the birth of the Sun was of the order of 107 years, and (iii) the abundances of the very short-lived nuclei 26Al, 36Cl, and 41Ca can be explained by massive star winds in single or binary systems, if these winds directly polluted the early Solar System. Our current and future work, as required to finalise the picture of the origin of radioactive nuclei in the Solar System, involves studying the possible origin of radioactive nuclei in the early Solar System from core-collapse supernovae, investigating the production of 107Pd in massive star winds, modelling the transport and mixing of radioactive nuclei in the galactic and molecular cloud medium, and calculating the galactic chemical evolution of 53Mn and 60Fe and of the p-process isotopes 92Nb and 146Sm. 

The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron capture process (r-process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives ( ≃ 15.6  million years ) of the radioactive r-process nuclei iodine-129 and curium-247 preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic ratio 129 I/ 247 Cm = 438 ± 184 with nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.