An all-sky map of half a million supermassive black holes

The Sloan Digital Sky Survey (SDSS) released Data Release 20, providing optical spectra for over 500,000 galaxies and identifying approximately 200,000 supermassive black holes through coordination with the eROSITA X-ray mission. The Black Hole Mapper program uses this data to measure black hole masses, growth rates, and distribution across cosmic time, offering the most comprehensive spectroscopic catalog of X-ray sources ever assembled. These findings reveal more giant black holes existed in the early universe than previously thought, providing new insights into supermassive black hole formation and evolution.