Understanding our Origins: Star Formation in H II Region Environments

Recent analysis of the decay products of short-lived radiounclides (SLRs) in meteorites, in particular the confirmation of the presence of live 60Fe in the early Solar System, provides unambiguous evidence that the Sun and Solar System formed near a massive star. We consider the question of the formation of low-mass stars in environments near massive stars, presenting a scenario for the evolution of a star and its disk around the periphery of an expanding H II region. The stages in this scenario begin with compression of molecular gas around the edge of an H II region, continue as forming stars are overrun by the advancing ionization front, and culminate when ejecta from one or more nearby supernova explosions sweeps over YSO disks located in the low density interior of the H II region, injecting SLRs including 26Al and 60Fe. We review the evidence that this mode of star formation is more characteristic of formation of low-mass stars than is the mode of star formation seen in regions such as the Taurus-Auriga molecular cloud. We discuss the implications of this scenario for our understanding of star formation, as well as the effects of the young Sun's astrophysical environment on the formation and evolution of the Solar System. We conclude that low-mass stars and their accompanying disks form and evolve very differently near massive stars than they do in regions like Taurus-Auriga, and that these differences have profound implications for our understanding of our origins.