Event

Whether dynamical systems such as galaxies, galaxy clusters and the universe itself are controlled by Einstein’s theory of gravity in conjunction with yet-to-be-identified dark matter/energy or alternatively by modified gravity is an outstanding current problem of astrophysics and fundamental physics. While the cold dark matter paradigm has been the main-stream view for galaxies for the last few decades, observed rotation curves of rotation-supported disk galaxies and their Kepler-like kinematic laws such as the baryonic Tully-Fisher relation and radial acceleration relation can be summarized by a remarkably simple phenomenological model of modified Newtonian dynamics based essentially on a single parameter of critical acceleration a0. This empirical phenomenology has aroused in recent years theoretical studies of modified gravity and dark matter nature. As an independent empirical study of the problem we focus on pure dispersion-supported massive galaxies, the dynamical opposite of rotation-supported galaxies. Selecting large numbers of bulge-dominate, nearly circular galaxies from the SDSS DR7 0.7 million galaxies and then stacking aperture velocity dispersions of the galaxies of the same luminosity, radius and light profile at different redshifts, we construct large numbers of velocity dispersion profiles (VDPs). By modeling VDPs using the spherical Jeans equation we investigate Kepler-like laws in dispersion supported systems and test independently dark matter and modified gravity theories.