Probing the Properties of Supermassive Black Holes

Abstract

The formation of supermassive black holes has been highly debated the past two decades, however there is still no general description of this process. This review paper discusses differences between theories in literature on how supermassive black holes formed - such as formation from the earliest stars, primordial black hole formation, and direct collapse formation - and provides some analysis of observable data which could distinguish them. While formation from the earliest stars is one of the first theories, it is unlikely to have happened due to lack of time for the stellar black hole to accrete enough mass to become a supermassive black hole. Nevertheless, we can change this theory so that either the supermassive black hole seed was massive to begin with (direct collapse formation) or there were other black holes before stellar ones (primordial black hole formation). Recently, NANOGrav caught a signal that may have come from a primordial black hole, meaning that primordial black hole formation theory is one of the main theories right now.