What radio observations teach us about stellar winds, accretion, and feedback in binaries

Binary systems containing a massive star and a compact object are excellent laboratories to study a wide range of extreme astrophysical processes. These binaries, intermediate stages in binary evolution towards merging compact objects, can launch powerful jets that shape their surroundings; they are key objects to understand accretion physics, from very low to extremely super-Eddington rates; and they can power the acceleration of particles to extreme energies, making them some of the brightest (transient )gamma-ray sources in the Milky Way. These processes are, fundamentally, caused by the launch of a strong stellar wind by the massive star, which interacts with the compact object to create these powerhouses of high-energy astrophysics.

The low-frequency properties of these binaries, in the radio and millimeter bands, offer a view of these energetic processes that remains more poorly explored than their high-energy emission. In this seminar, I will discuss several recent examples of using radio and millimeter observations to close this gap. I will show how these observations constrain the properties of stellar winds and reveal how effectively compact objects can accrete from them. I will also discuss efforts to find new binaries with compact objects — particularly with black holes — and how radio observations are essential in those searches.