Black hole spin: theory and observation

TL;DR

This paper reviews the theoretical background, observational techniques, and recent findings related to black hole spin, emphasizing its importance in understanding black hole formation, growth, and jet production.

Contribution

It provides a comprehensive overview of how black hole spin is modeled, measured, and interpreted in astrophysics, integrating recent observational campaigns and theoretical insights.

Findings

Spin affects accretion disk emission characteristics

Techniques for estimating black hole spin have advanced significantly

Recent measurements inform black hole formation and evolution models

Abstract

In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass has a standard Newtonian interpretation, the spin does not, with the effect of non-zero spin leaving an indelible imprint on the space-time closest to the black hole. As a consequence of relativistic frame-dragging, particle orbits are affected both in terms of stability and precession, which impacts on the emission characteristics of accreting black holes both stellar mass in black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN). Over the last 30 years, techniques have been developed that take into account these changes to estimate the spin which can then be used to understand the birth and growth of black holes and potentially the powering of powerful jets. In this chapter we provide a broad overview of both the theoretical effects of spin, the means by which it can be estimated and the results of ongoing campaigns.