The Dark Energy Spectroscopic Instrument (DESI) collaboration has publicly released its first major dataset, a groundbreaking collection of measurements that represents the largest three-dimensional map of the universe ever assembled. The DESI Data Release 1 (DR1), published at the end of March 2025, includes redshift information for 18.7 million celestial objects, of which 13.1 million are galaxies, 1.6 million are quasars, and four million are stars within the Milky Way. This release surpasses the output of all five generations of the Sloan Digital Sky Survey (SDSS) combined, marking a significant advancement in observational cosmology.
DESI is a U.S.-led project involving over 700 scientists worldwide. It operates from the 4-meter Mayall Telescope at Kitt Peak National Observatory in Arizona, using a custom-built instrument that allows simultaneous observation of 5,000 objects through robotic fiber-optic positioning systems. Since beginning its main survey in May 2021, DESI has rapidly collected data, achieving nearly 20 million redshift measurements in just 13 months.
Redshift, the stretching of light due to the expansion of the universe, allows scientists to determine the distance of celestial objects. With redshift data, astronomers can reconstruct the three-dimensional structure of the cosmos across billions of light-years. DR1 provides a precise map that reveals how matter is distributed in space and how that structure has changed over cosmic time.
The DESI DR1 release not only includes new data but also incorporates a uniform reprocessing of earlier survey validation observations, which were first made public in the DESI Early Data Release (EDR). These additional data bolster the consistency and scientific utility of the release, which spans a sky area of over 9,000 square degrees.
One of the most remarkable aspects of DR1 is the scope of its redshift survey. The galaxies cataloged range in distance from relatively nearby to as far back as 12 billion years ago, covering redshifts up to z ≈ 4. The dataset includes four main extragalactic target classes: bright galaxies (BGS), luminous red galaxies (LRG), emission-line galaxies (ELG), and quasars (QSO). These classes help probe different eras of cosmic history and provide complementary insight into the growth of structure in the universe.
DESI is also conducting an extensive survey of stars in the Milky Way. The Milky Way Survey (MWS) component of DR1 includes spectroscopic measurements that help astronomers analyze the chemical composition and motion of stars in the galactic halo, disk, and bulge. A visualization of the MWS data in DR1 reveals the structure of the Galaxy with unprecedented detail, including the metallicity gradient and features such as the Sagittarius stream and Monoceros ring, remnants of dwarf galaxies absorbed by the Milky Way in the past.
The data were processed using DESI’s Iron software pipeline, named after Iron Mountain in Utah. This processing included a full reanalysis of all prior survey validation data using updated calibration files and algorithms. The release also includes a supplemental dataset, named Guadalupe, based on the first two months of main survey operations. However, the primary scientific analyses moving forward are expected to rely exclusively on the Iron production due to its improved precision and larger sample size.
DESI classifies observations based on observing conditions: bright, dark, and backup programs. Bright-time observations include nearby galaxies and stars, while dark-time observations focus on more distant galaxies and quasars. Backup observations target stellar objects when sky conditions are not ideal. This strategic scheduling has allowed DESI to maximize its efficiency and scientific return, often measuring redshifts for over a million targets per month.
A critical component of DESI’s success lies in its target selection strategy. Using imaging data from the Legacy Surveys and Gaia mission, DESI identifies suitable targets across the sky, balancing scientific goals and practical considerations like brightness and observability. Primary targets include the main extragalactic and stellar samples, while secondary and tertiary targets support specific scientific goals such as calibration, peculiar objects, or underrepresented populations.
The scale of the DR1 dataset opens numerous opportunities for further research. Scientists will use the data to measure the baryon acoustic oscillation (BAO) signal, a subtle pattern in the distribution of galaxies that serves as a standard ruler for cosmology. BAO measurements allow precise constraints on the expansion history of the universe and, by extension, the properties of dark energy. DESI is the first of the so-called “Stage IV” dark energy experiments, designed to deliver next-generation cosmological precision.
In addition to dark energy studies, DESI data provide constraints on other cosmological parameters, including the sum of neutrino masses and signatures of early universe inflation. The sheer volume of data and its coverage across redshift and spatial scales enable rigorous testing of theoretical models.
The release is structured to support broad access. The DR1 portal provides access to reduced spectra, redshift catalogs, imaging data, and value-added products such as galaxy classifications and stellar parameters. Data visualization tools and documentation are available to facilitate usage by both professional astronomers and the broader research community.
The efficiency of DESI’s design and operations has allowed it to stay ahead of schedule, completing a significant portion of its five-year mission in record time. Its robotic fiber system and wide field-of-view allow the instrument to observe a vast number of targets in a single night. By the end of its survey in 2026, DESI is expected to have measured redshifts for over 50 million galaxies and quasars, along with detailed spectra for 25 million stars.
This release reflects not just a technical achievement but a strategic and collaborative effort among dozens of institutions across several continents. The DESI collaboration includes contributions from universities, national laboratories, and research institutes, demonstrating a model for large-scale scientific cooperation.
As the first year’s data become public, the scientific community is poised to make use of this rich resource. The scale and precision of DESI DR1 ensure it will be the basis of hundreds of studies in cosmology, galaxy evolution, and stellar astrophysics. Already, early scientific papers using subsets of the data have begun to appear, exploring clustering statistics, galactic structure, and more. With more data to come in future releases, the impact of DESI is only beginning to unfold.
Researchers are now able to examine questions that were previously out of reach, including the time evolution of galaxy clustering, the role of quasars in cosmic structure formation, and the metallicity distribution of stars in the galactic halo. DR1 includes value-added catalogs that streamline access to these subsets, enhancing the scientific usability of the raw data.
Beyond its role in dark energy research, DESI is also being used to explore phenomena such as galaxy mergers, star formation rates, active galactic nuclei, and galactic feedback processes. With its high spectral resolution and massive sample size, DESI enables statistical analyses that uncover rare and subtle trends. These insights feed into models of galaxy evolution that depend on accurate data across a wide range of conditions and environments.
DESI’s structure also provides a valuable template for future cosmology missions. The automated fiber positioning system, the modularity of the spectrographs, and the real-time data processing workflows serve as a testbed for even more ambitious future efforts. Lessons learned from DESI’s successes and challenges will influence the design and operation of space-based surveys, such as NASA’s Nancy Grace Roman Space Telescope and the ESA’s Euclid mission.
Public access to DESI DR1 is provided through the official DESI data portal. It includes tools to search and visualize data, access scripts and documentation, and interact with curated samples of interest. This infrastructure is intended to foster independent discovery and cross-institutional collaboration.
The broader community will be watching to see how the released data feed into refined measurements of cosmological parameters. With DESI aiming to constrain the nature of dark energy to within one percent accuracy, DR1 serves as the foundational dataset for this high-precision goal. By mapping galaxy distributions at different epochs in cosmic history, DESI provides a detailed timeline of the universe’s structure formation.
As with all large-scale survey efforts, maintaining consistency and calibration across time is essential. DESI’s meticulous control over instrument performance and its careful separation of observing programs into bright, dark, and backup categories helps mitigate potential sources of systematic error. This level of detail ensures that conclusions drawn from DR1 will rest on a reliable observational foundation.
Ultimately, the DESI DR1 release offers an unprecedented look at the universe’s structure, stretching from our own galaxy to galaxies seen as they were billions of years ago. It is the most ambitious and complete spectroscopic survey to date, and its impact will be felt across astrophysics and cosmology for years to come.
Source:
DESI Collaboration. “DESI Data Release 1.” arXiv:2503.14745v1, 27 Mar. 2025. https://arxiv.org/abs/2503.14745
