Observations of Early Black Holes Before and After JWST

Eduardo Banados

First listed 2026-03-23 | Last updated 2026-03-23

Abstract

These notes are from three lectures given at the 54th Saas-Fee Advanced Course of the Swiss Society of Astrophysics and Astronomy in January 2025. This chapter reviews the dramatic evolution in our understanding of supermassive black holes in the first billion years, from ground-based discoveries to recent space-based infrared observations with JWST. Section 1 introduces AGN and quasars to contextualise observations at the highest redshifts. Section 2 reviews the pre-JWST understanding of early quasars, including personal accounts of how key discoveries were made. Section 3 examines how JWST is transforming the field, from black hole mass measurements and host galaxy characterisation to large-scale environmental studies, and identifies emerging directions.

Short digest

Lecture notes from the 2025 Saas-Fee Course synthesize how our view of supermassive black holes in the first Gyr evolved from ground-based quasar finds to JWST-era infrared constraints. The chapter foregrounds a practical AGN–quasar luminosity taxonomy using M1450 and Lbol, stressing AGN as a time-variable phase and noting that JWST has uncovered AGN at redshifts beyond the most distant known quasars. It then surveys how JWST is reshaping the field—enabling black hole mass estimates, host-galaxy characterization, and environmental mapping—while connecting new results to the pre-JWST baseline. Scope note: the material reflects the state of the field as of January 2025 with targeted updates through early 2026.

Key figures to inspect

• Fig. 2 — Practical luminosity boundaries: read off the M1450 and Lbol demarcations (with the Runnoe+2012 conversion) to see where objects transition from galaxies → AGN → faint/bright quasars and where nomenclature becomes ambiguous.
• Fig. 1 — ChatGPT AGN–quasar comparison: use this pedagogical table to pinpoint why luminosity is the real separator and why the pre-JWST “distance” heuristic has been superseded by newer AGN at higher redshift.
• Fig. 14 — Reionization-era quasar census (pre-JWST baseline): inspect the redshift–luminosity coverage and selection footprint that anchor the historical census used throughout the notes.
• Fig. 33 — Updated quasar census: compare directly to Fig. 14 to visualize the JWST-era additions and how the redshift frontier and number counts have shifted; dataset link provided in comments.