Astrophysics Colloquium: Probing the physics of the early universe with pulsating stars

Pulsating ancient stars preserve information about distances, chemical composition and ages, offering a record of the early universe. This talk describes advances in stellar evolution and pulsation simulations, including machine-learning acceleration, that make these records useful for testing galaxy-formation models. Earl Patrick Bellinger examines RR Lyrae stars in the Galactic halo and Milky Way dwarf galaxies, and the nature of JWST Little Red Dots. A physics-informed approach to stellar pulsations enables distance estimates at approximately one-percent precision nearly to the Milky Way virial radius, supporting galactic archaeology and near-field cosmology. The talk also presents evidence for interpreting Little Red Dots as pulsating quasi-stars: black holes within supermassive, Cepheid-like stellar envelopes. If confirmed, this interpretation could explain both these objects and early supermassive black-hole growth.