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Simulations of Dense Stellar Systems at ECCA

(Staff: Douglas Heggie, Anna Lisa Varri)

Related Links:

The MODEST Project
The Globular Cluster M4
Internal rotations of clusters
Effect of external tidal field on clusters
Pressure anisotropy in clusters


ECCA Research

Dense stellar systems include galactic nuclei, young dense star clusters in star forming regions, and old globular clusters.  All three are active research areas for both theorists and observers.  Galactic nuclei harbour supermassive black holes, young dense clusters are the places where we can see the results of recent star formation, and globular star clusters are amazingly efficient at producing a bizarre mix of unusual stellar objects, such as millisecond pulsars, X-ray binaries and blue stragglers.  Understanding these objects involves the mutual influence of two processes: dynamics,  which deals with the motions of stars in the gravitational field they exert on each other, and stellar evolution, which is the process by which stars change in response to the generation of energy by nuclear reactions within them. This is the aim of the MODEST project, of which our work is a part.

Star cluster simulations

In Edinburgh we focus on simulating star clusters by two methods which simultaneously deal with the dynamics and the stellar evolution.  The first method is referred to as the direct summation method, in which the gravitational forces are computed from Newton's law of gravity.  This is extremely time consuming, and we use special-purpose hardware (called GRAPE), which does nothing but compute gravitational forces, but does it with far greater efficiency than a general-purpose computer.  The second method is a Monte Carlo method, which treats the dynamics on the basis of the approximate (but accurate) theory of  relaxation.  Roughly speaking, what this means is that the star cluster is treated like a gas, in which the stars are the atoms.  This is a much faster method than direct summation, which is too slow to deal with globular star clusters. At Edinburgh we are applying these methods to study the origin of blue stragglers stars in the globular star cluster M4, and other clusters.

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