Observations of Stellar-Mass Black Holes in the Galaxy

Abstract

Stellar-mass black holes (BHs), with masses comparable to stars, are a major constituent of our Milky Way galaxy. This chapter describes the landscape of challenging, and long-sought efforts to identify these objects in the Galaxy. The first stellar-mass BHs were identified as persistent, but highly variable cosmic X-ray sources. Later, transient BH candidates were detected, and now far outnumber the persistent sources. Decades of effort have also yielded candidate BHs via gravitational microlensing and their orbital effect on binary companions. Populations of BH systems have begun to emerge from these detection strategies, offering insight into the astrophysical context in which BHs exist and driving questions about the formation, assembly, and ongoing evolution of these enigmatic objects.