Carbon-Enhanced Dwarf Stars: Clues from the Galactic Halo
This study analyzed over 1,000 dwarf carbon stars using SDSS and Gaia data, providing the first reliable distances for such a large sample. The results show that about 60% belong to the Milky Way’s halo and 30% to the thick disc, confirming they are mostly old, metal-poor stars. These findings establish dwarf carbon stars as valuable tracers of the Galaxy’s early history and stellar evolution.
Untangling the Milky Way’s Halo with Aluminum
This study by Ernandes and collaborators shows that aluminum abundances ([Al/Fe]) are a powerful way to distinguish between stars formed inside the Milky Way and those accreted from dwarf galaxies. Using high-resolution spectra, they demonstrate that aluminum provides a cleaner separation than other elements, even at low metallicities. Their results refine previous classifications and highlight aluminum as a key tracer for unraveling the Galaxy’s merger history.
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.
Catching the Streams: Dynamical Moving Groups in the Milky Way’s Halo
This paper finds two inward-moving streams of halo stars, “Iphicles” and “the Beret”, near the Sun, likely caused by resonances with the Milky Way’s bar rather than past mergers. Using Gaia data and simulations, the authors show these streams trace the bar’s influence throughout the halo, helping measure the Galaxy’s mass and bar pattern speed.
How Did the Milky Way’s Halo Form? Designing the HALO7D-X Survey
The paper presents the HALO7D-X survey, designed to study the Milky Way’s stellar halo by combining Hubble, Gaia, and Keck data. Using simulations, the authors show the survey can distinguish whether the halo formed through many small early mergers or a few large later ones. HALO7D-X will reveal how the Galaxy’s halo assembled over time.
Spinning Up the Galaxy: How the Milky Way’s Bar Transfers Motion to Its Bulge and Halo
Using Gaia data and simulations, Zhuohan Li et al. identified a rotating group of stars in the Milky Way's bulge and halo. Their findings show that the central bar, slowing down over time, transfers angular momentum to these stars through resonance trapping. This process explains the unexpected rotation in regions once thought to be mostly static.
Unlocking the Secrets of the Stellar Halo: Dynamical Streams and the Galactic Bar
This study explores moving groups of stars in the Milky Way’s halo, revealing two streams influenced by the galaxy’s central bar. Using Gaia data and simulations, the authors show that these streams result from resonances with the bar’s rotation. By analyzing their motion, they estimate the Milky Way’s mass and bar pattern speed, refining our understanding of the galaxy’s structure and dynamics. Their findings highlight the role of resonances in shaping stellar motions.
Exploring the Invisible: Searching for Primordial Black Holes in the Milky Way
A study led by Przemek Mróz used the OGLE survey to search for primordial black holes (PBHs) as dark matter candidates in the Milky Way. Analyzing 20 years of data from 80 million stars, the team found no long-timescale microlensing events, placing strict limits on the contribution of PBHs to dark matter. These findings challenge theories linking PBHs to dark matter or black hole merger rates observed by gravitational wave detectors.
Tracing the Galactic Past: Linking Stars to Reticulum II’s Tidal History
Researchers traced the origins of r-process-enhanced stars in the Milky Way halo to the ultra-faint dwarf galaxy Reticulum II (Ret-II). Using advanced simulations and star catalogs, they identified 93 stars likely ejected from Ret-II over 11.5 billion years as it orbited the galaxy. This study highlights Ret-II’s role in the Milky Way’s formation and provides insights into the origins of heavy elements through cosmic events like neutron star mergers.
Unraveling the Galactic Halo: Identifying Components in the Milky Way’s Stellar Halo
Elliot Y. Davies and his team used a method called Non-negative Matrix Factorization (NMF) to separate the Milky Way’s stellar halo into distinct components based on chemical and spatial data. They identified both in-situ (formed within the Milky Way) and accreted (originating from other galaxies) stars, revealing that the inner halo is dominated by in-situ stars, while accreted stars prevail in the outer regions. Unique structures, such as "Eos" and "Aurora," suggest complex interactions between accreted and in-situ material, reflecting the galaxy's intricate formation history. This study sheds light on how the Milky Way evolved through both internal processes and mergers.