DESI team publishes largest 2D sky map: 4 billion objects, 5.6 trillion pixels

The DESI Legacy Imaging Surveys team has released the most detailed two-dimensional map of the universe ever assembled, stitching together 263,407 exposures taken over 2,285 nights into a 5.6-trillion-pixel image spanning roughly three-quarters of the sky. The map catalogs nearly 4 billion stars and galaxies in visible and near-infrared light, drawing on three ground-based surveys (DECaLS, MzLS, and BASS) plus data from NASA’s WISE satellite. The full dataset is public and browsable through the Legacy Survey Sky Viewer, and it has already become standard infrastructure for the field, cited in more than 1,800 papers.

The map’s core purpose is to feed the Dark Energy Spectroscopic Instrument (DESI), which uses it to pick targets and build a 3D map that tracks how galaxies cluster over cosmic time. That work is producing real stakes: DESI wrapped its five-year survey early in April 2026 and its preliminary data hints that dark energy may be weakening—a result that, if it holds, would rewrite predictions about the universe’s eventual fate. Because DESI observed galaxies faster than expected, the imaging map had to be expanded to keep supplying targets, and it has been guiding the telescope since June 2026.

The scale is as much a computing story as an astronomy one. Merging hundreds of thousands of frames shot under varying atmospheric and instrument conditions took about a year of code development and eight weeks of processing on the Perlmutter supercomputer at Berkeley Lab’s NERSC facility. Beyond DESI, the dataset is positioned as a reference baseline for next-generation observatories like the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, and as training material for AI tools meant to sift the petabytes of data those instruments will generate—including a planned astrophysics pilot in the DOE’s American Science Cloud.