Abstract: In the last decade gravitational wave astrophysics has revolutionized our understanding of stellar mass black holes, rapidly surpassing the sample known previously from electromagnetic observations. In parallel to gravitational wave discoveries, electromagnetic detections have started to unveil a new population of black hole binaries. These black holes orbit stars at longer periods than the regular X-ray binary population and exhibit no X-ray emission. Through astrometric, photometric and spectroscopic detections, this sample is expected to grow beyond a hundred sources in the coming years, providing new constraints on stellar evolution, binary physics and stellar dynamics. In this talk I will review the science deriving from these new electromagnetic detections, discuss the methods used to identify them, and how they will potentially clear long-standing theoretical questions.