arXiv subjects

Stephen L. W. McMillan

Publications and source records attributed to Stephen L. W. McMillan.

39 records · Page 3Linked to original sources

arXiv1996

Binary--single-star scattering VI. Automatic Determination of Interaction Cross Sections

Scattering encounters between binaries and single stars play a central role in determining the dynamical evolution of a star cluster. In addition, three-body scattering can give rise to many interesting exceptional objects: merging can produce blue stragglers; exchange can produce binaries containing millisecond pulsars in environments quite different from those in which the pulsars were spun up; various types of X-ray binaries can be formed, and their activity can be either shut off or triggered as a result of triple interactions. To date, all published results on three-body scattering have relied on human guidance for determining the correct parameter range for the envelope within which to perform Monte--Carlo scattering experiments. In this paper, we describe the first fully automatic determination of cross sections and reaction rates for binary--single-star scattering. Rather than relying on human inspection of pilot calculations, we have constructed a feedback system that ensures near-optimal coverage of parameter space while guaranteeing completeness. We illustrate our approach with a particular example, in which we describe the results of a three-body encounter between three main-sequence stars of different masses. We provide total cross sections, as well as branching ratios for the various different types of two-body mergers, three-body mergers, and exchanges, both non-resonant and resonant. The companion paper in this series, Paper VII, provides a full survey of unequal-mass three-body scattering for hard binaries in the point-mass limit.

astro-ph↗

arXiv1994

Gravitational Radiation from Coalescing Binary Neutron Stars

We calculate the gravitational radiation produced by the merger and coalescence of inspiraling binary neutron stars using 3-dimensional numerical simulations. The stars are modeled as polytropes and start out in the point-mass limit at wide separation. The hydrodynamic integration is performed using smooth particle hydrodynamics (SPH) with Newtonian gravity, and the gravitational radiation is calculated using the quadrupole approximation. We have run several simulations, varying both the neutron star radius and the equation of state. The resulting gravitational wave energy spectra $dE/df$ are rich in information about the hydrodynamics of merger and coalescence. In particular, our results demonstrate that detailed information on both $GM/Rc^2$ and the equation of state can in principle be extracted from the spectrum.

gr-qc↗

arXiv1993

Gravothermal Expansion in an $N$-Body System

This paper describes the numerical evolution of an $N$-body system with a slight ``temperature inversion''; i.e. the maximum velocity dispersion occurs not at the centre but further out. Fluid models predict that the core of such a system expands on a time-scale of thousands of central relaxation times, and here this behaviour is qualitatively confirmed for an $N$-body system of over 3000 bodies. With certain qualifications, this demonstrates the existence in N-body systems of one of the fundamental mechanisms which, in fluid models, drive the gravothermal oscillations discovered by Bettwieser & Sugimoto.

astro-ph↗