Astronomers released the 20th Data Release (DR 20) of the Sloan Digital Sky Survey on July 30th in the Astrophysical Journal Supplement Series, scaling the international project with over three million spectra of stars and galaxies, eighteen value-added catalogs, and its first Southern Hemisphere optical data.
When the Sloan Digital Sky Survey first started in 2000, it relied solely on an optical and spectral survey of the Northern Hemisphere conducted by a single 2.5-meter telescope. That legacy has evolved into a massive, multi-wavelength global collaboration. The twentieth data release marks the third installment of the project’s fifth phase, pushing the boundaries of what automated observatories can map across the night sky.
Southern Hemisphere Expansion and Optical Spectra
A major operational milestone anchors this latest release: the historic debut of SDSS-V stellar and extragalactic optical spectra observed from the Southern Hemisphere. Researchers gathered these observations using the du Pont 2.5m Telescope at Las Campanas Observatory in Chile, combining them with updated data from the Sloan Foundation 2.5m Telescope at Apache Point Observatory in New Mexico.
Dual-hemisphere access allows the survey to build a panoptic spectroscopic map of the cosmos. As part of this expansion, DR20 incorporates newly reduced spectroscopic data from the Baryon Oscillation Spectroscopic Survey obtained through February 2nd, 2025.
Mapping Supermassive Black Holes and X-Ray Sources
Beyond general stellar mapping, the release delivers a dramatic expansion for researchers tracking extreme cosmic phenomena. The Black Hole Mapper program grew three to fourfold over the previous data release, yielding roughly 1.1 million optical BOSS spectra for about 500,000 distinct objects.
This growth stems in part from automatic positioning robots at the observatories that handle fiber optics feeding the spectrographs, which enable faster and more accurate observations across the sky. Coordinate programs like the SPectroscopic IDentification of ERosita Sources bring in massive data streams from the second release of the eROSITA X-ray All-Sky Survey, identifying hundreds of thousands of active galactic nuclei, active stars, and galaxy clusters.
DR20 represents an enormous leap in the scale of SDSS data products — today we release over three million spectra of stars and galaxies along with 18 value added catalogs,
said Dr. Emily Griffith of University of Colorado Boulder, spokesperson for the SDSS-V collaboration. It’s the product of years of work by a dedicated, international team of astronomers. We’re excited to share DR20 with the world and see what the community discovers with it.
New Catalogs, Software Tools, and Interactive Visualization
The project extends far beyond raw spectral lines. The Milky Way Mapper program captured over three million total spectra encompassing 1.5 million stars, including rare finds like carbon-enhanced metal-poor stars in the Magellanic Clouds and an intermediate-mass stripped star. Meanwhile, the Local Volume Mapper scaled up significantly from its previous preview, releasing integral field spectroscopy maps across 169 tiles and 300,000 spectra to chronicle Galactic HII regions and planetary nebulae.
To help researchers and educators navigate this vast trove, the collaboration introduced LVMvis, a browser-based visualization tool featuring a detailed RGB emission-line HiPS map. Eighteen new or updated Value-Added Catalogs accompany these interfaces to streamline specialized academic research.
Collaborators emphasize that accessibility remains a central priority for the release. As Dr. Anne-Marie Weijmans, a researcher at the University of St Andrews and the SDSS Data Products Coordinator, said in an SDSS press release: “We want everyone to make use of the SDSS data products, whether they are a professional astronomer doing their research, a student learning how to work with data, a teacher looking for classroom material, or someone who is just interested in astronomy in general. That is why we have so many different platforms for people to interact with the data, and we take care to provide numerous examples and tutorials for each of these. The data should not just be publicly available but be publicly usable.”
Data Volume and Future Computational Demands
Looking ahead, the international team shows no signs of slowing down its observation schedules or data output. This data release provides some spectacular SDSS-V data that we are sure people will make excellent use of,
added Dr. Juna Kollmeier, a Staff Scientist at Carnegie Science and the Director of SDSS-V. But we aren’t stopping here. We just spent a week talking about what will go into DR21 and DR22! We’re going to need bigger computers!
