Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21742703c&link_type=abstract
American Astronomical Society, AAS Meeting #217, #427.03; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Despite being some of the most familiar objects observed in the sky, much remains unknown about open clusters. The theory of their formation admits many unanswered questions, and the complex dynamics of their evolution remains an extremely difficult problem to address. In this thesis, I present results that both help to constrain formation theories, as well as to shed new understanding on the many physical processes that drive their evolution.
Utilizing a series of N-body simulations, I argue that gravitationally bound stellar clusters of modest population evolve very differently from the picture presented by classical dynamical relaxation theory. The system's most massive stars rapidly sink towards the center and form binary systems. These binaries efficiently heat the cluster, reversing any incipient core contraction and driving a subsequent phase of global expansion. Most previous theoretical studies demonstrating deep and persistent dynamical relaxation have either conflated the process with mass segregation, ignored three-body interactions, or else adopted the artificial assumption that all cluster members are single stars of identical mass. In such a uniform-mass cluster, binary formation is greatly delayed, as I confirm here both numerically and analytically. The relative duration of core contraction and global expansion is effected by stellar evolution, which causes the most massive stars to die out before they form binaries. In clusters of higher N, the epoch of dynamical relaxation lasts for progressively longer periods. By extrapolating my results to much larger populations we can understand, at least qualitatively, why some globular clusters reach the point of true core collapse.
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