Observational Evidence for Black Holes

TL;DR

This paper reviews observational evidence for the existence of stellar-mass and supermassive black holes, their properties, and their influence on galaxy evolution, highlighting recent measurements of black hole spins and jet power correlations.

Contribution

It provides a comprehensive overview of black hole populations, their measured characteristics, and potential mechanisms powering relativistic jets, emphasizing recent observational advances.

Findings

Strong evidence for two black hole populations.

Correlation between supermassive black hole mass and galaxy properties.

Possible link between black hole spin and jet power.

Abstract

Astronomers have discovered two populations of black holes: (i) stellar-mass black holes with masses in the range 5 to 30 solar masses, millions of which are present in each galaxy in the universe, and (ii) supermassive black holes with masses in the range 10^6 to 10^{10} solar masses, one each in the nucleus of every galaxy. There is strong circumstantial evidence that all these objects are true black holes with event horizons. The measured masses of supermassive black hole are strongly correlated with properties of their host galaxies, suggesting that these black holes, although extremely small in size, have a strong influence on the formation and evolution of entire galaxies. Spin parameters have recently been measured for a handful of black holes. Based on the data, there is an indication that the kinetic power of at least one class of relativistic jet ejected from accreting black holes may be correlated with black hole spin. If verified, it would suggest that these jets are powered by a generalized Penrose process mediated by magnetic fields.