Young and intermediate-age massive star clusters

S.S. Larsen

    Research output: Contribution to journalArticleAcademicpeer-review

    Abstract

    An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>105 M⊙) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, Inline Formula, but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M>2×105 M⊙. In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several ×106 M⊙. The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.
    Original languageEnglish
    Pages (from-to)867-887
    Number of pages21
    JournalPhilosophical Transactions of the Royal Society. Mathematical, Physical and Engineering Sciences
    Volume368
    Issue number1913
    DOIs
    Publication statusPublished - 2010

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