Extension of General Relativity with MOND limit predicts novel orbital structure in and around galaxies

Detailed knowledge of the different classes of stellar orbits that can be accommodated in a given galactic potential is a prerequisite when building self-consistent models using for instance the Schwazschild technique. Furthermore, observational properties of galaxies depend on what these classes of orbits are and on the presence of chaos in the systems. In the realistic case in which the starting point for modeling is not a gravitational potential, but an observed density distribution, we will require a gravitational theory to make the connection between the stars that we see and the movement these stars may be having. The argument can be turned upside down: understanding what orbits may be allowed by each gravitational theory may give us a greater insight on what these theories are and on how we can test them. Our aim is thus to understand novel properties of orbits that are predicted by the latest extension of the MOND phenomenology into the relativistic world. We integrated orbits numerically in a fixed density distribution. The potential required for such integration was obtained also numerically by assuming different gravitational models. We find that thanks to the presence of a mass term in the field equations, the theory can allocate new classes of orbits that do not exist in Newtonian gravity nor standard MOND. We discuss consequences that these new families of orbits can have in non-linear cosmological structure formation as well as explore a possible alternative model for galactic structure based on them.