Activities in 1994-1995

From the Report for Academic Year 1994-1995
of the Institute for Advanced Study

PIET HUT continued his research in the general field of the dynamics of dense stellar systems. He visited Tokyo University during the summer of 1994, where he worked with Jun Makino on various projects. One of these involved the development of computer codes for the simulation of star cluster evolution on a new generation special-purpose computer, the Grape-4. During the summer, he also visited the Institute for Space and Aeronautical Sciences, and the Institute of Physical andChemical Research, both in Tokyo.

Further progress was made, throughout the year, on an ongoing project of studying gravitational three-body scattering, through a mixture of analytic and numerical approaches. In collaboration with Steve McMillan from Drexel University, Professor Hut continued the development of a comprehensive package that allows the automatic determination of cross sections and reaction rates for any type of stellar three-body encounters. This package was applied to the study of formation mechanisms of X-ray binaries and millisecond pulsars in globular clusters, in collaboration with Fred Rasio, a Member in the School of Natural Sciences.

In order to provide detailed models for the evolution of star clusters, including the interplay between stellar evolution and stellar dynamics, the first steps were taken towards an integration of both types of computational simulation. In collaboration with Simon Portegies Zwart from Utrecht University, a study was initiated of the formation and subsequent evolution of blue stragglers, products of direct physical collisions between individual stars in crowded stellar environments. Professor Hut also continued the development of the time symmetrization meta-algorithm that he had established the previous year with Makino and McMillan. Together with Yoko Funato, from Tokyo University, their symmetrization approach was extended to four-dimensional regularization techniques.

A new area of research with a widely interdisciplinary character, centered around the theme `limits to scientific knowledge', was introduced through two conferences under that title. The first one was held at the Santa Fe Institute in Santa Fe, New Mexico, and the second one in Abisko, Sweden, sponsored by the Swedish Academy of Sciences. Following the first conference, Professor Hut initiated a collaboration with cognitive psychologist Roger Shepard from Stanford University, funded by the Alfred P. Sloan Foundation.