A practical guide to the massive black hole cosmic history

TL;DR

This paper reviews the formation and evolution of massive black holes throughout cosmic history, emphasizing hierarchical growth, seed formation channels, and the potential of future gravitational wave observations to deepen understanding.

Contribution

It synthesizes current models of MBH formation and growth, highlighting the importance of hierarchical mergers and the need for future gravitational wave data to resolve existing uncertainties.

Findings

Hierarchical growth through mergers is the dominant paradigm.

Seed black holes likely formed via multiple channels at high redshift.

Upcoming gravitational wave observations will provide critical insights.

Abstract

I review our current understanding of massive black hole (MBH) formation and evolution along the cosmic history. After a brief introductory overview of the relevance of MBHs in the hierarchical structure formation paradigm, I discuss the main viable channels for seed BH formation at high redshift and for their subsequent mass growth and spin evolution. The emerging hierarchical picture, where MBHs grow through merger triggered accretion episodes, acquiring their mass while shining as quasars, is overall robust, but too simplistic to explain the diversity observed in MBH phenomenology. I briefly discuss which future observations will help to shed light on the MBH cosmic history in the near future, paying particular attention to the upcoming gravitational wave window.