Abstract

Abstract 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 million years. 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 × 104 pc−3 < n local < 2 × 105 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 ⊙) and intermediate-mass, compact clusters (M c < 3000 M ⊙). Present-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 the incorporation of constraints from cosmochemical studies.

Highlights

  • In recent years, first solar sibling candidates have been identified (Ramırez et al 2014; Bobylev & Bajkova 2014; Liu et al 2016; Martınez-Barbosa et al 2016; Webb et al 2019), which strengthens the earlier argument that the Sun was born as part of a group of stars (Adams 2010)

  • We want to have a look at the properties of the flybys that lead to solar system analogues (SSA)

  • We tried to constrain the type of stellar group that provided the birth environment of the solar system

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Summary

Introduction

First solar sibling candidates have been identified (Ramırez et al 2014; Bobylev & Bajkova 2014; Liu et al 2016; Martınez-Barbosa et al 2016; Webb et al 2019), which strengthens the earlier argument that the Sun was born as part of a group of stars (Adams 2010). In particular the presence of the short-lived radionuclides 60Fe and/or 26Al were used to estimate the number of stars/mass of the solar birth cluster (Thrane et al 2006; Dauphas & Chaussidon 2011; Adams et al 2014; Parker et al 2014; Lichtenberg et al 2016; Nicholson & Parker 2017). These calculations assume that these short-lived radionuclides were incorporated after a supernova outburst in the solar birth cluster. Very massive clusters with N > 105 have been excluded as solar birth clusters, because the correspondingly large number of very high-mass stars would produce a too strong radiation field (Hester et al 2004; Williams & Gaidos 2007)

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