Mapping Monsters: SDSS-V Data Release 20 Unveils All-Sky Views of Supermassive Black Holes - SDSS

Skip to content

News

Search

Theme -> Customize -> Widgets -->

The Black Hole Mapper reaches a milestone with its first southern hemisphere optical observations, coordinated eROSITA X-ray identification, and multi-epoch tracking of accreting black holes across the universe.

APACHE POINT OBSERVATORY, NM & LAS CAMPANAS OBSERVATORY, CHILE — The Sloan Digital Sky Survey (SDSS) announces Data Release 20 (DR20) , marking a landmark expansion in the study of accreting supermassive black holes (SMBHs). As part of the fifth generation of the survey (SDSS-V), the Black Hole Mapper (BHM) program is providing unprecedented insights into the masses, growth, and physics of quasars and active galactic nuclei (AGN) across cosmic time.

Sky distribution of DR20 astronomical objects targeted by the Black Hole Mapper (BHM) program in SDSS-V.<br>Image Credit: SDSS-V, Scott Anderson, University of Washington

DR20 delivers the first optical BOSS spectra from the southern hemisphere gathered at Las Campanas Observatory (LCO) in Chile, alongside expanded observations from Apache Point Observatory (APO) in New Mexico. In total, DR20 releases over 3.3 million optical spectra across 500,000 galaxies and 1.5 million stars, powering multi-wavelength discoveries in coordination with space-based observatories.

Unlocking the High-Energy Universe with eROSITA

Contacts

Scott Anderson<br>University of Washington<br>sfander@uw.edu

Andrea Merloni<br>Max-Planck-Institute for Extraterrestrial Physics<br>am@mpe.mpg.de

Mara Salvato<br>Max-Planck-Institute for Extraterrestrial Physics<br>mara@mpe.mpg.de

Yue Shen<br>University of Illinois<br>shenyue@illinois.edu

A core highlight of the Black Hole Mapper in DR20 is SPIDERS (SPectroscopic IDentification of ERosita Sources). By pairing SDSS optical spectroscopy with X-ray sky maps from the eROSITA mission, SPIDERS provides optical identifications and precise distance measurements (redshifts) for approximately 200,000 X-ray targets. This represents the largest, most uniform spectroscopic follow-up of X-ray sources ever assembled.

While SPIDERS captures tens of thousands of X-ray-emitting galaxy clusters and energetic star systems, the vast majority of these high-energy beacons are actively accreting supermassive black holes —known as active galactic nuclei (AGN) or quasars.

Mapping Cosmic Structure and Black Hole Demographics

X-ray emission acts as a beacon, allowing astronomers to peer directly into the central engines of these giant black holes and probe the hot X-ray coronae surrounding them. By measuring the "X-ray luminosity function"—essentially a census tracking how many black holes exist across different power outputs and cosmic eras—scientists can trace supermassive black hole growth from our cosmic neighborhood back to redshifts near six, pushing into the early Universe’s "cosmic dawn."

Thanks to the combined wide-sky coverage of SDSS and eROSITA, this new dataset provides the tightest constraints to date on the rarest, most luminous quasars. The survey reveals more giant black holes early on and higher space densities of the most luminous AGN at high redshifts than previously expected. This reveals that rapidly growing giant black holes were surprisingly common in the early Universe. More “hidden” black holes have been uncovered,where traditional optical and UV sky surveys miss a substantial fraction of accreting black holes, particularly at lower luminosities and extreme distances. Also, by calculating total accumulated black hole growth over time, researchers found that soft X-ray-selected black holes account for only a minority of total black hole mass in the local Universe. This implies that 70% to 90% of all supermassive black hole growth occurred behind heavy veils of dust and gas, or during phases where even X-rays were suppressed.

"This release marks the culmination of more than a decade of joint planning and scientific exchange between the German eROSITA Consortium and the Sloan Digital Sky Survey", said Dr. Andrea Merloni , eROSITA Principal Investigator and BHM Survey Scientist. "With DR20, we demonstrate not only that combining the X-ray and optical spectroscopic data opens up new and original scientific perspectives in astrophysics, but also that large, international and diverse collaborations can effectively work together for years towards a common goal."

Probing the Inner Workings of Quasars Through Time

Because supermassive black holes themselves are too distant and compact to image directly, BHM leverages the hallmark variability of quasars across multiple time-domain sub-programs:

By capturing rapid, repeated spectra of targeted quasar fields over timescales ranging from days to years, the BHM Reverberation Mapping (RM) program measures time delays between light emitting from the central accretion disk and the surrounding broad-line region. This yields direct, geometric measurements...