The creation of the largest-ever three-dimensional map of the universe, containing data on more than 47 million galaxies and quasars, represents a major milestone in observational cosmology. This map was produced by the Dark Energy Spectroscopic Instrument (DESI), an international scientific collaboration led by the Lawrence Berkeley National Laboratory. Installed on the Nicholas U. Mayall Telescope in Arizona, DESI is specifically designed to measure the expansion history of the universe with high precision.
DESI began its primary survey operations in 2021. Over the course of approximately five years, the instrument has collected spectroscopic data from tens of millions of celestial objects. The dataset includes more than 47 million galaxies and quasars, along with roughly 20 million stars within the Milky Way. The resulting dataset significantly exceeds earlier large-scale surveys in both volume and depth.
How the 3D Map Is Constructed
The defining feature of this map is that it is three-dimensional. Unlike traditional sky surveys that provide two-dimensional images, DESI determines the distance to each observed galaxy using a method based on redshift. As light from distant galaxies travels through expanding space, its wavelength stretches toward the red end of the spectrum. By measuring this shift through spectroscopy, scientists can calculate how far away a galaxy is and how fast it is receding. This allows researchers to place galaxies in a 3D framework, where distance corresponds to looking back in time.
Mapping the Universe Across Cosmic Time
The map extends across a large portion of the observable universe, reaching distances of up to approximately 11 billion light-years. This means that the survey captures light emitted when the universe was significantly younger. One of the key epochs included in the dataset is known as cosmic noon, which occurred roughly 8 to 11 billion years ago. During this period, the rate of star formation in galaxies was at its highest. Observing galaxies from this epoch allows scientists to study how structures formed and evolved over time.
DESI uses a highly efficient data collection system involving 5,000 robotic fiber-optic positioners. These robotic devices can rapidly align with selected targets in the sky and capture their spectra simultaneously. Each exposure allows DESI to gather light from thousands of galaxies at once, enabling it to survey large areas of the sky quickly and systematically. This high-throughput capability is a key factor behind the scale of the dataset.
The Cosmic Web Structure
The spatial distribution of galaxies in the DESI map reveals the large-scale structure of the universe, often referred to as the cosmic web. This structure consists of interconnected filaments of galaxies and galaxy clusters, separated by vast regions known as voids where relatively few galaxies exist. The cosmic web arises from the growth of initial density fluctuations following the Big Bang. Over billions of years, gravity amplified these fluctuations, leading to the formation of the structures observed today.
Studying Dark Energy
One of the primary scientific goals of DESI is to investigate the nature of dark energy. Dark energy is a form of energy that permeates space and is responsible for the accelerated expansion of the universe. It is estimated to constitute approximately 68–70% of the total energy density of the universe. By mapping the positions of galaxies across different epochs, DESI enables precise measurements of how the expansion rate of the universe has changed over time.
A key technique used in this analysis involves studying patterns known as baryon acoustic oscillations (BAO). These are regular, periodic fluctuations in the density of visible matter that originated in the early universe. The scale of these oscillations provides a “standard ruler” for measuring cosmic distances. By comparing the observed distribution of galaxies to this known scale, scientists can infer the expansion history of the universe with high accuracy.
Implications for Cosmology
Early findings from DESI data have provided detailed measurements of cosmic expansion across a wide range of redshifts. These measurements are being used to test the standard cosmological model, often referred to as Lambda-CDM, which includes dark energy in the form of a cosmological constant. The DESI dataset allows for tighter constraints on cosmological parameters than previous surveys.
Ongoing Research and Future Goals
The project is ongoing and is expected to continue observations through 2028. By the end of its mission, DESI aims to map more than 50 million galaxies and quasars. The increasing size and precision of the dataset will support further analysis of galaxy clustering, the growth of structure, and the properties of dark energy.
In addition to its primary cosmological objectives, the DESI dataset also supports a wide range of astrophysical studies. These include investigations into galaxy evolution, quasar activity, and the structure of the Milky Way. The inclusion of millions of stellar spectra provides valuable data for understanding the composition and dynamics of our own galaxy.
All data collected by DESI are processed and made available to the scientific community through periodic data releases. These datasets are used by researchers worldwide to conduct independent analyses and to cross-check cosmological models. The scale and precision of the DESI map make it one of the most comprehensive resources currently available for studying the universe.
The 47-million-galaxy 3D map produced by the Dark Energy Spectroscopic Instrument is the largest and most detailed map of the universe to date. It combines spectroscopic measurements, large-scale survey techniques, and advanced instrumentation to provide a comprehensive view of cosmic structure and evolution over billions of years.
