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.