Gaia's faintest stars

Abstract

In the Brief History of Time Stephen Hawking was pessimistic about astronomers detecting primordial black holes (PBHs). He would not be the only distinguished scientist to underestimate the extraordinary power of new technology. In a related area Albert Einstein published the equations for microlensing, but wrote off their practicality. Perhaps they meant "during my lifetime." The amazing properties of PBHs, however, validate heroic efforts to detect them. If they exist, their niches in our current history of time include supplying dark matter to bind galaxies, offering a solution for the Hubble tension, and, as supermassive black holes, giving us quasars as far as the eye can see. This Research Note describes a search for PBHs in the Gaia archive. In spite of the high density of local dark matter, it was unsuccessful. Microlensing with the Rubin telescope is the tool at our disposal to open the asteroid window for PBH.