Monte-Carlo simulations of globular cluster dynamics

We present the results of theoretical calculations for the dynamical evolution of dense globular star clusters. Our new study was motivated in part by the wealth of new data made available from the latest optical, radio, and X-ray observations of globular clusters by various satellites and ground-based observatories, and in part by recent advances in computer hardware. New parallel supercomputers, combined with improved computational methods, now allow us to perform dynamical simulations of globular cluster evolution using a realistic number of stars (N - 10 - 106) and taking into account the full range of relevant stellar dynamical and stellar evolutionary processes. These processes include two-body gravitational scattering, strong interactions and physical collisions involving both single and binary stars, stellar evolution of single stars, and stellar evolution and interactions in close binary stars. We have developed a new numerical code for computing the dynamical evolution of a dense star cluster. Our code is based on a Monte Carlo technique for integrating numerically the Fokker-Planck equation. We have used this new code to study a number of important problems. In particular, we have studied the evolution of globular clusters in our Galaxy, including the effects of a mass spectrum, mass loss due to the tidal field of the Galaxy, and stellar evolution. Our results show that the direct mass loss from stellar evolution can significantly accelerate the total mass loss from a globular cluster, causing most clusters with low initial central concentrations to disrupt completely. Only clusters born with high central concentrations, or with relatively few massive stars, are likely to survive until the present and remain observable. Our study of mass segregation in clusters shows that it is possible to retain significant numbers of very-low-mass (m < 0.1M.) objects, such as brown dwarfs or planets, in the outer halos of globular clusters, even though they are quickly lost from the central, denser regions. This is contrary to the common belief that globular clusters are devoid of such low-mass objects. We have also performed, for the first time, dynamical simulations of clusters containing a realistic number of stars and a significant fraction of binaries. We find that the energy generated through binarybinary and binary-single-star interactions in the cluster core can support the system against gravothermal collapse on timescales exceeding the age of the Universe, explaining naturally the properties of the majority of observed globular clusters with resolved cores.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2000

Author dc:creator

• Joshi, Kriten J. (Kriten Jayant), 1971-

Advisor dc:contributor.advisor

• Frederic A. Rasio.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/53041

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/53041