Raga (Relaxation in Any Geometry) is a program for simulating the dynamical evolution of non-spherical stellar systems using the Monte Carlo approach. Its main features are:
Simulation of stellar systems with a much smaller number of particles N than the number of stars in the actual system;
Representation of an arbitrary non-spherical potential with a multipole (spherical-harmonic) expansion, with the coefficients of expansion computed from particle trajectories;
Two-body relaxation modelled by local (position-dependent) velocity diffusion coefficients (as in Spitzer's Monte Carlo formulation); the magnitude of relaxation can be adjusted to the actual number of stars in the target system and is not related to the number of particles in the simulation;
Particle trajectories are computed independently and in parallel, using a high-accuracy adaptive-timestep integrator; the potential expansion and diffusion coefficients are updated at rather long intervals (possibly comprising many dynamical times, but much shorter than the relaxation time);
Can model the effect of a central massive black hole (capture of low angular momentum stars) and a binary massive black hole (scattering of stars and shrinking of the binary);
The method is described in the paper in MNRAS/446/3150 (2015); the modification to deal with a massive binary black hole is described in another paper.
The current version is 3.0, which now has an interface to the AMUSE framework and is capable of simulating systems with a spectrum of stellar masses.
Version 2.0 was a major redesign of the code; it is now based on the Agama library and included in its distribution.
Earlier versions can be downloaded here: 1.1, 1.0. They require additional libraries: GSL, and optionally Odeint and UNSIO.
More information can be found in the readme file.
© 2013—2020 Eugene Vasiliev
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