The Sloan Digital Sky Survey (SDSS) announces Data Release 20 (DR20), a landmark expansion in the study of accreting supermassive black holes. As part of SDSS-V's Black Hole Mapper (BHM), DR20 delivers the first optical BOSS spectra from the southern hemisphere at Las Campanas Observatory, alongside expanded observations from Apache Point Observatory. In total, DR20 releases over 3.3 million optical spectra across 500,000 galaxies and 1.5 million stars.

The SPIDERS program pairs SDSS optical spectroscopy with X-ray maps from eROSITA, providing identifications and redshifts for approximately 200,000 X-ray targets—the largest uniform spectroscopic follow-up of X-ray sources ever assembled. This reveals more giant black holes in the early universe and uncovers hidden black holes missed by optical surveys.

Researchers found that 70% to 90% of all supermassive black hole growth occurred behind heavy veils of dust and gas. The BHM's Reverberation Mapping and All-Quasar Multi-Epoch Spectroscopy programs track quasar variability to measure black hole masses and dynamical changes. The robotic focal plane system enables rapid multi-object observations across both hemispheres.

All DR20 data are openly available to researchers and the public. "Quasars have long been known to vary," said SDSS-V Director Juna Kollmeier, "and it is extremely exciting to be at the point where we can use those variations at scale."