The first supermassive black holes in the universe

Black holes, one of the most intriguing predictions of Einstein’s general relativity, have been a focus of astrophysical research for more than 50 years. Study of astrophysical black holes covers a wide range of mass scales, employing different detection methods. Stellar mass black holes- products of collapse of massive stars at the end of their lifetimes - are detected as invisible but massive members of binary systems that usually emit highenergy photons through gas accretion around the black holes; their masses range from a few to a few tens of solar masses. Intermediate mass black holes are thought to reside in centers of globular clusters or dwarf galaxies, with masses of the order hundreds to tens of thousands solar masses. For the cosmologist, however, the key interests lie in the study of supermassive black holes located in the nuclei of galaxies, with masses ranging from million to billion solar masses. Their mass can be measured by observing gas and stellar motion in the center of nearby galaxies. During the periods when these supermassive black holes are actively accreting matter, the resultant radiation from the accretion process can often outshine the entire galaxy - which we usually refer to as quasars, or active galactic nuclei (AGNs). The formation of supermassive black holes is now believed to have played a key role in the evolution of galaxies, and in the evolution of the thermal state of the Universe. The most luminous quasars are powered by black holes in the billion solar mass range, and are tens of thousands times brighter than normal galaxies, therefore detectable at great distance, providing powerful light beacons to probe the most distant and oldest epoch of the Universe. One of the key interests in modern cosmology is to understand when and how the first generation supermassive black holes occurred in the Universe, and how they are related to the first generation of galaxies. In this chapter, we first review the observational signatures of supermassive black holes and their connections to galaxy evolution, then discuss the current observations of the most distant quasars and their supermassive black holes, and the questions these observations posed to early cosmic evolution. We will discuss the basic physical processes that produced the earliest supermassive black holes and how the next generation observing facilities will be able to enable us to probe the evolution of the first supermassive black holes in the Universe.