When Galaxies Collide: How a Cosmic Merger Twists Stellar Streams
Claire Guillaume and collaborators used detailed simulations to study how a galactic merger distorts stellar streams, thin trails of stars orbiting the Milky Way. They found that mergers create lasting asymmetries between the leading and trailing arms of these streams, especially for those on wide orbits. These distortions can persist for billions of years, complicating efforts to use stellar streams to map dark matter.
How the Milky Way’s Disc Survived a Cosmic Collision
This paper explores how the Milky Way’s disc formed and survived an ancient collision with the Gaia-Sausage-Enceladus galaxy. Using simulations and Gaia data, Orkney and colleagues show the disc was already spinning about 11 billion years ago and that the merger was likely minor, not major. Despite disruption, the disc reformed, with starbursts and globular clusters marking the event’s impact.
Faint Streams Hidden in Plain Sight: What the Mass–Metallicity Relation Tells Us About Tidal Disruption
Alexander Riley and collaborators use the Auriga simulations to test whether the mass–metallicity relation of galaxies rules out tidal disruption. They find that even heavily stripped satellites still follow the relation with little scatter, matching what’s seen in the Milky Way and Andromeda. This suggests many Local Group satellites have lost large fractions of their stars, and faint tidal streams may be revealed by future surveys.
A Massive Ancient Merger: Tracing the Origins of the Gaia–Enceladus Galaxy
Plevne and Akbaba use Gaia and APOGEE data with machine learning to identify Gaia–Enceladus stars and model the galaxy’s chemical evolution. They estimate its initial gas mass at about 4.9 billion Suns, making it one of the Milky Way’s most massive accreted satellites. The results suggest a short, intense star formation period, strong outflows, and a merger that ended star formation within the first 4 billion years.
How Galactic Collisions Sculpt the Cosmos: The Impact of Merger Orbits on Galaxy Structure
Wu et al. study how the paths of galaxy mergers affect the resulting structure using simulations. They find that spiral-in orbits tend to preserve disks, while head-on collisions destroy them and build bulges and halos. The hot inner stellar halo grows in nearly all mergers, making it a strong indicator of merger history.