Activities in 1986-1987

From the Report for Academic Year 1986-1987
of the Institute for Advanced Study

PIET HUT concentrated his research on the interface between computer science and astrophysics. He continued a long-term collaboration with Sussman, from the Artificial Intelligence Laboratory at M.I.T., aimed towards developing a ``computational observatory''. Specifically, Hut developed a new gravitational many-body code which provided a ``work-bench'' for testing a wide range of old and new methods in an integrated environment; Hut and Sussman investigated general individual timestep predictor-corrector algorithms for integrating the equations of motion of long-range forces; Barnes and Hut performed a detailed error analysis for a novel tree-type algorithm for performing N-body calculations, developed by them in the previous year; Hut and Makino performed a detailed study of the cost-effectiveness of existing N-body codes, developed a general theoretical foundation for such an analysis and suggested optimal values for tuning parameter which before had been determined only empirically; Aarseth, Hut and McMillan investigated modifications for existing Aarseth-codes necessary for treating higher numbers of particles than treated before.

Hut continued his collaboration with Heggie, working towards a comprehensive analytical understanding of three-body scattering cross sections and reaction rates. Hut and Teuben started a systematic study of the interaction and merging of small stellar systems. Together with McMillan, and Casertano, Hut studied the relaxation rates in small star systems; they confirmed the theoretical scaling with particle number, but found a larger time scale than expected. Hut and Inagaki continued their investigation of stochastic heating of globular cluster cores by binary reactions.

Another field of interdisciplinary research in which Hut was active was a collaboration between four paleontologists (including Erle Kauffman and Gerta Keller), two geologists (including Walter Alvarez) and two astronomers. They finished an ongoing collaboration, resulting in a comprehensive paper which addressed the possibility of comet showers causing mass extinctions, in a critical comparison of material from all three disciplines.