M87: a cosmic laboratory for deciphering black hole accretion and jet formation

TL;DR

This paper reviews recent observational and theoretical advances in understanding the supermassive black hole in M87, focusing on accretion processes and jet formation, enabled by high-resolution imaging and multi-wavelength data.

Contribution

It provides a comprehensive synthesis of multi-wavelength observations and theoretical insights into M87's black hole, highlighting new imaging capabilities of the event horizon and jet structures.

Findings

First event-horizon-scale images of an AGN obtained.

Detailed understanding of jet collimation and propagation.

Insights into accretion processes near the black hole.

Abstract

Over the past decades, there has been significant progress in our understanding of accreting supermassive black holes (SMBHs) that drive active galactic nuclei (AGNs), both from observational and theoretical perspectives. As an iconic target for this area of study, the nearby giant elliptical galaxy M87 has received special attention thanks to its proximity, large mass of the central black hole and bright emission across the entire electromagnetic spectrum from radio to very-high-energy gamma rays. In particular, recent global millimeter-very-long-baseline-interferometer observations towards this nucleus have provided the first-ever opportunity to image the event-horizon-scale structure of an AGN, opening a new era of black hole astrophysics. On large scales, M87 exhibits a spectacular jet propagating far beyond the host galaxy, maintaining its narrowly collimated shape over seven orders of magnitude in distance. Elucidating the generation and propagation, as well as the internal structure, of powerful relativistic jets remains a longstanding challenge in radio-loud AGNs. M87 offers a privileged opportunity to examine such a jet with unprecedented detail. In this review, we provide a comprehensive overview of the observational knowledge accumulated about the M87 black hole across various wavelengths. We cover both accretion and ejection processes at spatial scales ranging from outside the Bondi radius down to the event horizon. By compiling these observations and relevant theoretical studies, we aim to highlight our current understanding of accretion and jet physics for this specific object.