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Paper: The Early Sun: Evolution and Dynamic Environment
Volume: 341, Chondrites and the Protoplanetary Disk
Page: 54
Authors: Reipurth, B.
Abstract: An overview is given of the astrophysical processes that govern the formation and early evolution of solar-like stars, specifically aimed at meteoriticists. After a discussion of the various types of protostars and young stars and of the collapse process, the importance of binary and multiple star formation is emphasized. The frequency and properties of young binaries as derived from observations are summarized. Theoretical work demonstrates how newborn multiple stars are unstable and decay on short time scales to stable configurations, often ejecting lower-mass members through dynamical interactions. Observations of phenomena like Herbig-Haro jets and FU Orionis eruptions find a natural explanation within a scenario involving the evolution of small multiple systems and the resulting formation of close binaries. It is emphasized that the vast majority of stars in our Galaxy are formed in clusters, but that most of these clusters dissolve soon after the remaining gas has been dispersed and the gravitational potential that held the cluster together therefore is weakened. Thus, while most stars are born in clusters, only a small fraction will remain in clusters lasting hundreds of millions of years. The likelihood that the early Sun was a member of a temporary cluster at birth and perhaps even a member of a small multiple system is stressed. Possible relic evidence that the Sun was part of a cluster of a few thousand stars includes the solar obliquity, the detection of traces of 60Fe in ordinary chondrites, the sharp edge of the Kuiper belt, and the discovery of distant large objects in eccentric orbits like Sedna. The meteoritic record must be examined with the possibility in mind that the early Sun may well have been a member of a long gone cluster and that the early solar nebula may have been affected by close passages of sibling stars.

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