Origins of Supermassive Black Holes in Galactic Centers

TL;DR

This paper reviews the origins of supermassive black holes, focusing on seed formation, current challenges, and potential observational signatures, with implications for understanding galaxy evolution and testing models with upcoming telescopes.

Contribution

It provides a comprehensive overview of SMBH seed formation theories, challenges in modeling, and discusses observable signatures for future testing.

Findings

Seed black holes likely formed from multiple pathways.

Observational signatures could distinguish formation scenarios.

Future facilities like JWST and LISA will test these models.

Abstract

Direct imaging of black hole shadow halos has firmly confirmed the existence of supermassive black holes (SMBHs), with millions of solar masses, residing at the centers of the Milky Way and M87 galaxies. These groundbreaking discoveries represent a monumental success of Einstein's theory of general relativity and have revealed the hidden "monsters" lurking at the centers of galaxies. Moreover, observations of active galactic nuclei (AGNs) indicate that SMBHs with billions of solar masses were already in place within the first billion years after the Big Bang. However, the origins of these SMBHs, as well as their co-evolution with host galaxies, remain poorly understood. This review focuses on the origin of SMBHs, particularly on the formation of their seed black holes. We also highlight several outstanding challenges in modeling seed formation and discuss possible observational signatures. These signatures may be testable with current and future facilities, including the James Webb Space Telescope (JWST) and the upcoming gravitational wave observatory, the Laser Interferometer Space Antenna (LISA).