Astrometry seminars

Pulsating ancient stars preserve information about distance, chemical composition and age that can constrain the early history of galaxies. Earl Patrick Bellinger describes advances in stellar-evolution and pulsation simulations, together with machine-learning acceleration, that allow these stellar records to test models of galaxy formation. The talk develops two applications. RR Lyrae stars trace the Galactic halo and Milky Way dwarf galaxies; a new physics-informed approach to their observations enables distance precision of about one percent almost to the Milky Way’s virial radius, supporting galactic archaeology and nearby-universe cosmology. For the distant universe, the presentation examines JWST’s Little Red Dots and evidence for an interpretation as pulsating quasi-stars: black holes surrounded by supermassive, Cepheid-like stellar envelopes. If confirmed, this interpretation could explain both the Little Red Dots and the early formation of supermassive black holes.

Subha Majumdar presents a six-dimensional Milky Way phase-space catalogue designed to map stellar motions and dark matter beyond the reach of Gaia parallaxes alone. Gaia astrometry is combined with spectrophotometric distances and radial velocities from fourteen surveys, including DESI, SDSS-BOSS, APOGEE and LAMOST. The resulting catalogue contains about 33 million tracers and detailed distance–velocity measurements for roughly half a million halo stars. It characterizes distant clusters, dwarf galaxies and stellar streams, enabling mass modeling, kinematic studies, abundance mapping, Galactic archaeology and dark-matter searches. An application constructs a continuous Galactic rotation curve extending to 250 kiloparsecs.