A numerical study of the stability of spherical galaxies
Abstract
The stability of spherical nonrotating galaxies is examined by using an Nbody code to evolve a set of initially equilibrium models which are generated from three distribution functions. All the models have the same initial density profile which is essentially a de Vaucouleurs law. The first family of models is characterized by a velocity ellipsoid which becomes increasingly radial. The second family is predominantly radial at the center; and the third family has a constant anisotropy. It is found that the three families were all unstable to the formation of a bar when the velocity distribution was sufficiently anisotropic. In the first family of models, the transition to instability occurred suddenly as anisotropy increased. The numerical results are inconsistent with a recent proof of the stability of a wide class of anisotropic systems. The instability of radially anisotropic models suggests that an initially spherical cloud that is sufficiently cold will form a bar during collapse. In order to test the above hypothesis, the collapse and virialization of galaxies were simulated starting from spherical initial conditions with various temperatures. It is found that inclusion of less than about 10 percent of the initial energy in random motions leads to the formation of a bar.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 1985
 DOI:
 10.1093/mnras/217.4.787
 Bibcode:
 1985MNRAS.217..787M
 Keywords:

 Astronomical Models;
 Elliptical Galaxies;
 Galactic Structure;
 Many Body Problem;
 Systems Stability;
 Anisotropic Media;
 Computational Astrophysics;
 Galactic Evolution;
 Astrophysics