Fifty Years After the Discovery of the First Stellar-Mass Black Hole: A Review of Cyg X-1

TL;DR

This review discusses 50 years of research on Cyg X-1, highlighting its significance in understanding stellar-mass black holes, accretion physics, and high-energy plasma phenomena through X-ray observations.

Contribution

It synthesizes recent X-ray observational results on Cyg X-1, emphasizing black hole spin, accretion geometry, and plasma physics insights, advancing understanding of black hole systems.

Findings

Cyg X-1 hosts a ~20 solar mass black hole.

X-ray data reveal details of accretion and plasma physics.

Implications for black hole spin and stellar evolution.

Abstract

Around 50 years ago, the famous bet between Stephen Hawking and Kip Thorne on whether Cyg X-1 hosts a stellar-mass black hole became a well-known story in the history of black hole science. Today, Cyg X-1 is widely recognised as hosting a stellar-mass black hole with a mass of approximately 20 solar masses. With the advancement of X-ray telescopes, Cyg X-1 has become a prime laboratory for studies in stellar evolution, accretion physics, and high-energy plasma physics. In this review, we explore the latest results from X-ray observations of Cyg X-1, focusing on its implications for black hole spin, its role in stellar evolution, the geometry of the innermost accretion regions, and the plasma physics insights derived from its X-ray emissions. This review primarily focuses on Cyg X-1; however, the underlying physics applies to other black hole X-ray binaries and, to some extent, to AGNs.