Observing Fundamental Dynamics in the Milky Way: Stream Morphologies, Separatrices, and Dark Matter Potentials

Stellar streams, formed from the tidal disruption of globular clusters and dwarf galaxies, have long been used as dynamical tracers to help characterize the Milky Way’s gravitational potential and its dark matter halo. Recent observations have revealed that some streams, such as Jhelum, Atlas Aliqa Uma (AAU), and Palca, exhibit more complex morphologies, including fans, bifurcations, and multiple separate components. I will explain how such features can arise from transitions, or separatrices, between the orbit families supported by non-spherical potentials. In the particular case of the three aforementioned streams, I will show simulations of objects on similar orbits exhibiting morphological features that result from this dynamical mechanism, and that are reminiscent of the observed systems. I will discuss how these findings may be used to help determine the precise shape of the gravitational potential of the Milky Way’s halo.