DESI observes the sky from the Mayall Telescope, shown here beneath the Milky Way. Credit: KPNO/ NOIRLab/ NSF/ AURA/ RT Sparks.

A new data release from the Dark Energy Spectroscopic Instrument (DESI) is now available for researchers to explore.

The collection contains information on 18.7 million galaxies, quasars, and stars — the largest dataset of its kind ever shared

The Dark Energy Spectroscopic Instrument (DESI) is mapping millions of celestial objects to better understand dark energy: the mysterious driver of our universe’s accelerating expansion.

Now, the DESI collaboration has released a new collection of data for anyone in the world to investigate.

The dataset is the largest of its kind, with information on 18.7 million objects: roughly four million stars, 13.1 million galaxies, and 1.6 million quasars (extremely bright but distant objects powered by supermassive black holes at their cores). 

While the experiment’s main mission is illuminating dark energy, DESI’s Data Release 1 (DR1) could yield discoveries in other areas of astrophysics, such as the evolution of galaxies and black holes, the nature of dark matter, and the structure of the Milky Way.

Stephen Bailey, a scientist who leads data management for DESI and works at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), said: “DR1 already gave the DESI collaboration hints that we might need to rethink our standard model of cosmology.

“But these world-class datasets are also valuable for the rest of the astronomy community to test a huge wealth of other ideas, and we’re excited to see the breadth of research that will come out.”

The Dark Energy Spectroscopic Instrument maps the universe by collecting spectra from millions of galaxies and quasars. Credit: Marilyn Sargent/ Berkeley Lab.

International experiment

DESI is an international experiment that brings together more than 900 researchers from over 70 institutions.

The new dataset vastly expands DESI’s Early Data Release (EDR), containing roughly ten times as much data and covering seven times the area of sky.

DR1 includes information from the first year of the ‘main survey’ collected between May 2021 and June 2022, as well as from the preceding five-month ‘survey validation’ where researchers tested the experiment. 

Objects in DESI’s catalogue range from nearby stars in our own Milky Way to galaxies billions of light-years away.

Because of the time it takes light to travel to Earth, looking out in space is akin to looking back in time.

DESI lets us see our universe at different ages, from the present day to 11 billion years ago.

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 one million objects in a single month.

For comparison, its predecessor, the Sloan Digital Sky Survey (SDSS), collected light from nine 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.

David Schlegel, one of the lead scientists at Berkeley Lab for both DESI and SDSS, said: “The DESI project has maintained the pace of making 3D maps of the universe that are ten times larger every decade.

“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.”

This slice of the DESI data maps celestial objects from Earth (centre) to billions of light years away. Among the objects are nearby bright galaxies (yellow), luminous red galaxies (orange), emission-line galaxies (blue), and quasars (green). The large-scale structure of the universe is visible in the inset image, which shows the densest survey region and represents less than 0.1% of the DESI survey’s total volume. Credit: Claire Lamman/ DESI collaboration.

Large-scale science for a large-scale audience

DESI collects light from distant galaxies by using 5,000 fibre-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.

John Moustakas, a professor of physics at Siena College and co-lead of DR1, said: “DESI is unlike any other machine in terms of its ability to observe independent objects simultaneously.”

The instrument separates the light from each galaxy into its spectrum of colours.

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.

Every night, the images taken by DESI are automatically transferred to supercomputers at NERSC.

The facility analyses the data and sends them back to the researchers — a process they’re proud to advertise as ‘redshifts before breakfast’.

This data transfer takes place via ESnet, the DOE’s dedicated high-speed network for science.

The approach represents a new way of doing research where experimental facilities and data analysis are tightly coupled.

This ecosystem forms an integrated research infrastructure that drastically accelerates the pace of science.

Daniel Margala, a scientific data architect at NERSC and part of the team that supports the DESI data processing, said: “For this data release, we made it so DESI could run on our most advanced supercomputer, Perlmutter.”

The transition to Perlmutter lets researchers take advantage of the supercomputer’s powerful GPUs (graphics processing units), processing the data nearly 40 times faster than was possible on previous NERSC systems.

Margala added: “What would have taken months on Cori [a prior-generation supercomputer] takes only weeks on Perlmutter.”

Star trails over the Mayall Telescope that houses DESI. Credit: Luke Tyas/ Berkeley Lab and KPNO/ NOIRLab/ NSF/ AURA.

Creative ideas

Even though they analyse data every night, researchers are always making improvements to their code to get the most possible information out of the light they collect.

Once they hit a milestone, like collecting data for one year, they reprocess the full dataset with the best version of the code.

It took about a month to crunch the DR1 dataset on Perlmutter.

That speed will be important as DESI collects even more data. The project is currently in its fourth of five years of data collection and aims to record spectra for more than 50 million galaxies and quasars before it ends.

Collaborators within DESI hope the experiment’s data will benefit researchers and enable those without access to large telescopes to advance their work.

A major component of the data release is documentation to support other scientists, even those unfamiliar with the project, in understanding its contents. 

Anthony Kremin, a project scientist at Berkeley Lab who co-led processing of the new data release, said: “We’re still discovering all the things you can do with this dataset, and we want the community to be able to try out all their creative ideas.

“There are endless kinds of interesting science you can do when you combine our data with outside information.”