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Cradle(s) of the Sun

The Sun likely formed as part of a group of stars. A close stellar flyby by one of the solar siblings is probably responsible for the sharp outer edge in the solar system`s mass distribution. The frequency of such close flybys can be used to determine the likely type of birth environment of the solar system. Young stellar groups develop very quickly, expanding significantly within just a few Myr. Here we model this strong dynamical development of young stellar groups and determine the resulting close flyby history. We find that solar system equivalents are predominantly produced in areas with stellar densities in the range 5 $\times$ 10$^4$ pc$^{-3}<$ n$_{local} <$ 2 $\times$ 10$^5$pc$^{-3}$. Remarkably we find that only two very distinct types of stellar groups can be considered as serious contestants as the cradle of the Sun -- high-mass, extended associations ($M_c >$ 20 000 $M_{sun}$) and intermediate-mass mass, compact clusters ($M_c <$ 3000 $M_{sun}$). Current day counterparts would be the association NGC 2244 and the M44 cluster, respectively. In these two types of stellar groups, close flybys take place at a sufficiently high rate, while not being too destructive either. A final decision between these two remaining options will require incorporation of constraints from cosmo-chemical studies.