Astronomy Colloquium

Aleksey Generozov, The University of Texas at Austin

What Can We Learn from the Young Stars in the Galactic Center?

The central parsec of our Galaxy contains young stars orbiting Sgr A*, a supermassive black hole, including the isotropic S star cluster of B stars within ~0.04 pc of the central SMBH. The presence of these young stars so close to Sgr A* has been a long-standing puzzle. I will discuss how binary disruptions can explain these stars and their orbits. Furthermore, the young stars serve as tracers for the dynamics in the innermost reaches of the Galaxy, probing otherwise hard-to-detect populations of stellar mass black holes.

Alessandra Venditti, The University of Texas at Austin

The Surprising Lives of Pop III Stars: Whens, wheres and hows

The search and characterization of the first (Population III or Pop III) stars is a central goal of modern astrophysics. These stars are predicted to start forming at Cosmic Dawn (z~20−30) from molecular-cooling mini-halos (~105−106 M⊙), and to be predominantly massive, shaping early galaxy evolution, cosmic metal enrichment and reionization. However, theory also allows efficient Pop III formation in pristine clouds within high-mass, atomic-cooling halos (≳108 M⊙), potentially persisting well into the Epoch of Reionization (EoR, z~6−10) and coexisting with second-generation (Pop II) stars. JWST has opened concrete prospects for detecting such systems. Tentative constraints on the Pop III UV luminosity function at z≃5.6−6.6 hint at an unexpectedly UV-bright Pop III population, and candidate Pop III systems have been reported at z~3−10 using joint low-metallicity and spectral-hardness diagnostics. Yet no Pop III-dominated galaxy has been confirmed, motivating the need for broader searches and robust confirmation strategies. I will discuss interpretations of these exciting findings, and outline avenues for identifying Pop III stars in and around massive EoR galaxies via HeII rest-frame UV and optical lines, while also quantifying confusion from nearby young Pop II populations.