Orbits in a Neighboring Dwarf Galaxy According to MOND

We study the orbits in the MOND theory within a dwarf galaxy of mass Md at a distance of ~100kpc from a neighboring galaxy of mass Mg, such as ours. It is assumed that a second mass m<<Md is gravitationally bound to Md by a previously calculated potential for the MOND theory. This potential is obtained for a free falling mass Md in a constant external gravitational acceleration field. The numerical technique of surfaces of section is used to study the stability of the phase-space orbits in the dwarf galaxy. Equatorial orbits with sufficiently small eccentricities e<0.65 are found to be stable with respect to small chang es in the initial conditions. (The equatorial plane is perpendicular to the direction of the external gravitational acceleration, which is along the line joining Md and Mg.) For decreasing values of the conserved component of the angular momentum, in the direction of the external gravitational acceleration, equatorial stability is lost.