By precisely measuring the motions stars on the sky over time, the Gaia mission is conducting a comprehensive census of the Milky Way's binary stars. These data are transformative both for population modeling and for discovery of rare objects. I will describe our emerging view of the populations of black holes, neutron stars, and white dwarfs in au-scale binaries, focusing in particular on their mass, period, and eccentricity distributions. Compared to previous surveys, Gaia is revealing post-interaction binaries in wider orbits, whose properties are difficult to explain with standard binary evolution models. I will discuss how the Gaia catalogs can be leveraged for statistical inference, despite their complex selection function, and how they can discriminate between competing formation models.

Speaker: Kareem El-Badry (California Institute of Technology)

The 2025 Fall Colloquium talks are held on Wednesdays at 3:00 PM. This colloquium is hosted by STScI and will be held as an in-person and virtual event.

You may join in person at STScI’s John N. Bahcall Auditorium or virtually on the STScI Research YouTube channel.

Please direct questions or comments to contact above. The 2025 Fall Colloquium Committee members are: Nimisha Kumari (STScI), Elena Manjavacas (STScI), Jack Neustadt (JHU), Kevin Schlaufman (JHU), Adam Smercina (STScI), Ethan Vishniac (JHU).