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.
A Galaxy in Transition: Tracing the Milky Way's Disc Evolution After the Gaia-Sausage-Enceladus Merger
Funakoshi et al. examine how the Milky Way’s disc evolved following the Gaia-Sausage-Enceladus merger. They identify a key transition around 10 billion years ago from a compact thick disc to a growing thin disc, with a brief dip in disc scale length. This dip, supported by simulations, suggests the galaxy’s gas disc temporarily shrank due to changing gas accretion modes during this transformative period.
Tracing Ancient Mergers in the Heart of the Milky Way: RR Lyrae Stars and the Gaia-Enceladus/Sausage in the Inner Stellar Halo
Kunder et al. study RR Lyrae stars in the Milky Way’s inner halo to trace remnants of the ancient Gaia-Enceladus/Sausage merger. They find about 6-9% of these stars show motions and metallicities consistent with GES, less than in the solar neighborhood. Their results match simulations showing GES debris is less concentrated near the Galactic center.
Tracing the Milky Way’s Past: How Globular Clusters Reveal the History of the Gaia-Sausage-Enceladus Merger
Fernando Aguado-Agelet and colleagues studied 13 globular clusters linked to the Gaia-Sausage-Enceladus (GSE) merger to trace the Milky Way’s history. They found most clusters follow a clear age-metallicity pattern, with two distinct star-formation bursts about 2 billion years apart, likely triggered by GSE’s interaction with the Milky Way. Two clusters probably formed in the Milky Way, and two others may belong to different mergers.
Galactic Ripples in a Turbulent Sea: Can Phase Spirals Survive the Clumpy Interstellar Medium?
The paper explores whether the Milky Way’s phase spiral—a ripple in stellar motion—can persist in a clumpy, star-forming interstellar medium. Simulations show that while smooth, gas-free discs best preserve the spiral, turbulence from star formation can still support it. However, overly clumpy gas suppresses the pattern, making the spiral a sensitive probe of galactic structure and dynamics.
Chasing a Galactic Starburst: Clues from the Milky Way’s High Proper-Motion Stars
This study uncovers a unique group of stars, called LAHN stars, that likely formed during a major merger between the Milky Way and the Gaia-Sausage/Enceladus galaxy. Their distinct chemical signatures and orbits suggest a burst of star formation triggered by the collision. These stars help reveal how such events shaped the Milky Way’s early evolution.
The Ancient Roots of the Milky Way’s Disks: Evidence for Early Co-Formation Before a Galactic Collision
Borbolato et al. find that the Milky Way’s thin and thick disks began forming over 11 billion years ago, earlier than previously thought. Using stellar ages and chemistry from APOGEE, LAMOST, and Gaia data, they show both disks co-formed, challenging models that rely on a major merger to start thin disk formation. Instead, the Gaia-Sausage Enceladus event likely halted thick disk growth and boosted thin disk star formation.
Unearthing Ancient Stars: The Discovery of Two Metal-Poor R-Process Enriched Stars
Astronomers discovered two ancient metal-poor stars enriched in r-process elements, shedding light on the origins of heavy elements. BPS CS 29529-0089, an r-II star, likely formed in the Milky Way’s proto-disk, while TYC 9219-2422-1, an r-I star, originated in the Gaia-Sausage-Enceladus merger. Their chemical signatures suggest enrichment by neutron star mergers and possibly a single Population III supernova, challenging existing theories on galactic evolution.
NGC 288: The First "Splashed" Globular Cluster?
NGC 288 appears to be the first known "Splashed" globular cluster—originally formed in the Milky Way but later thrown into a new orbit by the Gaia-Sausage-Enceladus (GSE) merger. Despite its accreted-like motion, its age and chemical composition match in situ clusters, suggesting it was born in the Milky Way. This study highlights how ancient galaxy mergers reshaped the Milky Way's structure, potentially affecting other globular clusters in similar ways.
Decoding Galactic History: How the Milky Way’s Disk Thickness Tells the Tale of Cosmic Collisions
The study reveals the Milky Way’s merger history through its disk thickness, using stellar age data and simulations. Key events include the Gaia-Sausage-Enceladus merger 11 billion years ago and interactions with the Sagittarius dwarf galaxy. Simulations confirm these patterns, showing a transition from a thick to thin disk over billions of years. Despite uncertainties, the findings provide a robust method to trace galactic evolution.
Exploring the History of the Milky Way with Gaia’s Giant Stars
The study uses Gaia data and machine learning models to estimate the ages of giant stars, revealing insights into the Milky Way's evolution. By analyzing over 2.2 million stars, the researchers identified three major phases in the galaxy's history, including a starburst triggered by a major merger and the formation of the thin disc. Their method advances our ability to trace the Milky Way's structure and development.
Exploring Black Holes in Dwarf Galaxies: Insights from Omega Centauri
This study by Limberg explores the proposed intermediate-mass black hole (IMBH) in Omega Centauri (ωCen), a stripped nuclear star cluster thought to be from the dwarf galaxy Gaia-Sausage/Enceladus. It extends known relationships between black hole mass, stellar mass, and velocity dispersion to dwarf galaxies, suggesting such galaxies follow similar evolutionary patterns as larger systems. The findings emphasize the importance of studying IMBHs to understand black hole formation and their role in galaxy evolution.
Unveiling the Milky Way’s Past: Insights from Dwarf Galaxies and Simulations
The study by François Hammer and collaborators examines the Milky Way's accretion history by comparing observational data, including globular clusters and dwarf galaxies, to predictions from cosmological simulations. They find that older mergers align well with simulations, but most dwarf galaxies appear to have been captured relatively recently, contradicting simulation predictions. The study highlights mismatches in rotation curves and binding energy distributions, suggesting current models need refinement. The work concludes that more realistic simulations are required to accurately capture the Milky Way's mass distribution and evolutionary history.
Investigating the Milky Way’s Thin Disk Evolution Through Solar Twins
The study by Anastasiia Plotnikova investigates the chemical evolution of the Milky Way’s thin disk by analyzing solar twins—stars similar to the Sun. Using high-resolution spectroscopy, the team examined the age-metallicity relationship (AMR) and found no evidence for a split into distinct populations, challenging previous studies. They suggest that radial migration and galaxy mergers, like the Gaia-Enceladus/Sausage event, significantly shape the disk’s chemical composition, indicating a more continuous, smooth evolution of the thin disk than previously thought.
Exploring the Milky Way's Proto-Galaxy: A Chemical and Structural Investigation Using APOGEE-Gaia
This study by Horta and Schiavon uses data from the APOGEE and Gaia surveys to investigate the Milky Way's proto-galaxy—its earliest stellar components. By analyzing the chemical compositions and distribution of ancient stars, the authors identify distinct populations, including those from the galaxy's main progenitor and from past mergers like Gaia-Sausage-Enceladus. Using a Plummer model, they estimate the mass of the proto-galaxy to be about 9.1 x 10^8 solar masses, providing insights into the early formation of the Milky Way and its structural evolution.
Star Formation History of Gaia-Sausage-Enceladus: What Elemental Abundances Reveal
The study by Ernandes et al. investigates the star formation history of the Gaia-Sausage-Enceladus (GSE) galaxy using elemental abundances from its stars. The results show that GSE's star formation began gradually and extended for over 2 billion years. However, it ended abruptly, likely due to its merger with the Milky Way. Comparing GSE's chemical patterns to dwarf galaxies like Sculptor and Fornax reveals that GSE's history was similar to Fornax's slow growth but was cut short by external forces.