DESI Opens Access to the Largest 3D Map of the Universe Yet

Although DR1 is just a fraction of what DESI will eventually produce, the 270-terabyte dataset represents a staggering amount of information, including precise distances to millions of galaxies. The release contains more than twice as many extragalactic objects (those found outside our galaxy) as have been collected in all previous 3D surveys combined. 

Within its first year of operations, DESI became the single largest spectroscopic redshift survey ever conducted, sometimes capturing data on more than 1 million objects in a single month. For comparison, its predecessor, the Sloan Digital Sky Survey (SDSS), collected light from 9 million unique objects over roughly 25 years of operations. In 2024, DESI researchers used the data in DR1 to create the largest 3D map of our universe to date and make world-leading measurements of dark energy.

“The DESI project has maintained the pace of making 3D maps of the universe that are 10 times larger every decade,” said David Schlegel, one of the lead scientists at Berkeley Lab for both DESI and SDSS. “That’s our version of Moore’s Law for cosmology surveys. The rapid advance is powered by the clever combination of improved instrument designs, technologies, and analysis of ever-fainter galaxies.”

DESI collects light from distant galaxies by using 5,000 fiber-optic “eyes.” Under clear observing conditions, the instrument can gather a new set of 5,000 objects roughly every 20 minutes, or more than 100,000 galaxies in one night. “DESI is unlike any other machine in terms of its ability to observe independent objects simultaneously,” said John Moustakas, a professor of physics at Siena College and co-lead of DR1. 

The instrument separates the light from each galaxy into its spectrum of colors. This lets researchers determine how much the light has been “redshifted,” or stretched toward the red end of the spectrum by the universe’s expansion. Measuring the redshift of light from a distant object tells scientists how far away it is, meaning DESI can map the cosmos in three dimensions and reconstruct a detailed history of cosmic growth.