SpaceTime

This image from the Hubble Space Telescope shows the small galaxy called the Sagittarius dwarf irregular galaxy, or "SagDIG" for short. SagDIG is relatively nearby, and Hubble's sharp vision is able to reveal many thousands of individual stars within the galaxy. Credit: NASA, ESA, and The Hubble Heritage Team STScI/AURA As one of the most massive Milky Way satellites, the Sagittarius dwarf galaxy has played an important role in shaping the Galactic disk and stellar halo morphologies. The disruption of Sagittarius over several close-in passages has populated the halo of our Galaxy with large-scale tidal streams and offers a unique diagnostic tool for measuring its gravitational potential. In a recent paper (Dierickx, Loeb 2017) the authors test different progenitor mass models for the Milky Way and Sagittarius by modeling the full infall of the satellite. They constrain the mass of the Galaxy based on the observed orbital parameters and multiple tidal streams of S