Unraveling the Cocytos Stream: A Stellar Fossil from the Milky Way’s Past
The Cocytos stream is a newly characterized stellar stream likely formed from a disrupted globular cluster brought into the Milky Way by the Gaia–Enceladus merger. It is unusually metal-rich and thick for such streams, with an orbit and composition linking it to other ancient merger remnants like the Virgo Overdensity. This discovery sheds light on the galaxy’s complex formation history.
Unraveling the GD-1 Stream and Its Mysterious Cocoon: A DESI Perspective
The study by Valluri et al. uses DESI data to confirm a cocoon surrounding the GD-1 stellar stream—a broader, kinematically hotter structure with a common origin. Possible explanations include pre-accretion stripping, debris from a parent galaxy, interactions with dark matter subhalos, or perturbations from the Sagittarius dwarf galaxy. Future DESI observations will help determine the cocoon’s origin, providing insights into the Milky Way’s evolution and dark matter structure.