The oldest stars in the Milky Way provide a glimpse into both the formation of the first stars and the earliest stage of the assembly of an L* disk galaxy. I'll describe the discovery and characterization of an ultra metal-poor binary star system on a thin disk orbit. The secondary is a star near the hydrogen burning limit and is the first very low-mass ultra metal-poor star known. The secondary most likely formed via disk fragmentation, and I'll use this discovery and theoretical models to argue that solar-mass fragments should form via disk fragmentation and survive around massive Population III stars. The system is the most metal-poor thin disk star system by some margin, and its age of more than 13 Gyr indicates that the thin disk of the Milky Way is several Gyr older than usually thought. The implication is that the Milky Way may have had an unusually quiescent merger history.
Followed by wine and cheese in Pupin 1402.