Department of Astronomy & Physics
Time: November 8, 2019 - 3:00 PM
Location: Atrium 101
Stars escaping globular clusters form thin, long and kinematically-cold tidal streams. In pristine conditions, these streams have nearly uniform density, however, new Gaia observations of one such structure in the Milky Way halo have revealed a likely site of perturbation. In this talk, I will show that the on-sky morphology suggests a recent, close encounter with a massive and dense perturber. Known baryonic objects are unlikely perturbers based on their orbital properties, but observations permit a low-mass dark-matter subhalo as a plausible candidate. This discovery opens up the possibility that detailed observations of streams could measure the mass spectrum of dark-matter substructures and even identify individual substructures and their orbits in the Milky Way halo. I will discuss the observational and modeling efforts I am leading to follow up this feature, review prospects for discovering evidence of similar events in other stellar streams, and forecast the sensitivity of stellar streams to low-mass perturbers in the era of LSST.