SCYON Abstract

Received on January 4 2001

The Birth, Evolution and Death of Star Clusters

Authors	Pavel Kroupa
Affiliation	University of Kiel
To appear in	Origin and Evolution of Young Stellar Clusters, Asp. Conf. Series, eds T. Montmerle and Ph. Andre
Contact	pavel@astrophysik.uni-kiel.de
URL	http://xxx.uni-augsburg.de/abs/astro-ph/0010405
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Abstract

A dense-enough gas-accumulation evolves, over a few Myr of intensifying star formation, to an embedded cluster. If it contains a sufficient amount of mass, O stars form and explosively expel the remaining gas, whereas poorer clusters reduce their embryonic gas content more gradually. The sudden expulsion of gas unbinds most of a rich cluster, but a significant fraction of it can condense by two-body interactions to become an open cluster despite a star-formation efficiency as low as 30 per cent. Poorer clusters survive their gradual mass loss more easily, but have short, relaxation-limited life-times. Pleiades-like clusters may thus form as nuclei of expanding OB associations, by filling their tidal radii and having large (1-2 pc) core-radii. A 'main-sequence' of clusters is thus established. Ultimately, a cluster dies an explosive death through the ever shortening relaxation time, and leaves a remnant that consists of about 4-10 stars arranged in a highly hierarchical and thus long-lived system. Dynamical mass segregation in very young clusters is extremely rapid, and heats a cluster substantially, which is partially off-set by the cooling from the disruption of primordial binaries.