An astronomical instrument equipped with 5.000 robotic optical fibers has achieved something that sounded like science fiction just a few decades ago: creating the largest three-dimensional map of the universe ever constructed. It's not just a spectacular image of the sky, but a detailed record that allows us to trace the history of cosmic expansion and challenges some of the most established ideas about how the cosmos works.
This gigantic catalog, based on the light from tens of millions of galaxies, quasars, and stars , is revealing evidence that dark energy—the mysterious component driving the accelerated expansion of the universe—may not behave as stably as previously thought. If these results are confirmed, current cosmological models will have to be carefully revisited.
DESI: the instrument that has changed the scale of maps of the cosmos
The instrument responsible for this feat is the Dark Energy Spectroscopic Instrument (DESI). It is installed on the four-meter Nicholas U. Mayall Telescope at the Kitt Peak National Observatory in Arizona (USA) and is part of an international collaboration involving more than 900 scientists from 75 institutions and 14 countries.
DESI uses an array of 5.000 optical fibers controlled by tiny robots capable of orienting themselves, each night, toward thousands of different galaxies. Each fiber is adjusted with a precision of about 10 microns—much less than the thickness of a human hair—to position itself precisely over the point in the sky from which light is to be collected. This beam of light is broken down into its spectrum, allowing scientists to calculate the distance, speed, and other physical properties of each object.
Thanks to this technology, the instrument can observe more than 100.000 galaxies per night , a rate that has increased the amount of available data sixfold compared to all previous cosmological surveys combined. DESI has taken advantage of both dark nights, ideal for studying the most distant objects, and periods with a moon, when it has focused on closer stars and structures.
The main observation campaign, designed to last five years, was completed even ahead of schedule despite serious unforeseen events such as the COVID-19 pandemic and the 2022 Contreras fire, which directly threatened the observatory's facilities. Even so, the team managed to maintain its pace and finish collecting data in record time.
The largest 3D map of the universe: 11.000 billion light-years of history
The result of this coordinated effort is a three-dimensional map spanning some 11.000 billion light-years in depth. This means that DESI is recording galaxies that emitted the light we see today when the universe was only about 2.700 billion years old, very close to the beginning of its history, estimated at about 13.700 billion years.
In total, the project has cataloged more than 47 million galaxies and quasars , as well as nearly 20 million stars in our own Milky Way. All of this is represented on a 3D map where each point indicates the position of one of these cosmic objects and how they are grouped on a large scale, forming a kind of "cosmic web" of filaments and voids.
With this map, astronomers can track how the distribution of galaxies has changed over time and reconstruct the so-called expansion history of the universe . The key lies in very precisely measuring the redshift of light from each galaxy—that is, how its wavelength has been stretched as space itself expands while the light travels to us.
DESI has mapped approximately one-third of the sky , and project managers plan to expand that coverage even further. The goal is to increase the observed area by about 20%, reaching approximately 17.000 square degrees. For comparison, the fingernail of your little finger at arm's length covers about one square degree, while the full moon occupies about 0,2 square degrees.
What does the map tell us about dark energy?
While the map itself is impressive, DESI's primary ambition wasn't so much to map the sky in greater detail, but rather to use that information to better understand dark energy . This component, which neither emits nor absorbs light, is considered responsible for the ever-accelerating expansion of the universe and is estimated to represent around 70% of the total content of the cosmos.
For years, the standard model of cosmology has assumed that dark energy behaves as a cosmological constant , a term introduced by Albert Einstein in the general theory of relativity to explain the uniform expansion of space. In practice, this means that its intensity does not change appreciably over time: it always behaves in the same way throughout the history of the universe.
DESI's observations, however, are beginning to paint a more nuanced picture. Analysis of how galaxies cluster over those 11.000 billion years suggests that dark energy might be a dynamic phenomenon, not perfectly constant . Already in preliminary results presented in 2025, the team indicated that the "antigravitational" effect of this energy might be weakening slightly over time.
If this trend is confirmed upon completion of the analysis of all the collected data, it would imply a profound change in the cosmological model . Researchers such as astronomer Luz Ángela García and cosmologist Young Wook Lee have long pointed out that these types of results open the door to a new theoretical framework for understanding the balance between matter and energy in the cosmos and its future evolution.
A different future for the universe?
Until now, the most widespread view was that the universe would continue to expand at an accelerating rate indefinitely, driven by a virtually immutable dark energy. In that scenario, over billions of years, galaxies would become increasingly isolated until they formed a cold, dark, and practically empty cosmos , where gravity could no longer regroup matter on a large scale.
The DESI findings point to something more complex. If dark energy weakens over time, gravity could regain ground in the distant future. Some theoretical models suggest that, at a certain point, this recovery could slow down the accelerated expansion and even reverse it.
In that extreme scenario, the universe could head towards a situation known as the Big Crunch . Instead of expanding forever, the cosmos would eventually collapse in on itself: galaxies would begin to move closer together, distances would shrink, and in the final stages, all matter and energy would be compressed into an extremely dense and hot state.
It is important to emphasize that, for now, these scenarios remain very long-term hypotheses . No one is claiming that the Big Crunch will definitely happen, but the DESI data compels us to seriously consider possibilities that until recently were seen as merely marginal. What does seem clear is that dark energy might not be as simple as a fixed constant in the equations.
Dark matter, stellar streams, and dwarf galaxies
The value of DESI is not limited to the study of dark energy. The three-dimensional map is also providing highly detailed information about dark matter , that other invisible component that constitutes most of the mass of the universe and that decisively influences how galaxies form and cluster.
By analyzing the position and motion of millions of galaxies, astronomers can infer how dark matter, which is not directly visible but whose gravity leaves its mark on the large-scale structure , is distributed . Furthermore, the project aims to study dwarf galaxies and stellar streams in the vicinity of the Milky Way with particular attention.
These streams are bands of stars that have been pulled from smaller galaxies by the gravitational pull of our own. Following their shape and trajectory allows us to reconstruct the type of dark matter halo that surrounds the Milky Way and better understand how it has grown by absorbing smaller systems over billions of years.
By incorporating areas closer to our galaxy into its mapping, including regions where starlight or atmospheric conditions hinder observations, DESI aims to create a more homogeneous picture of the sky. This expanded version of the map will help further refine models of cosmic structure formation, from local scales to the largest volumes of the observable universe.
An unprecedented technological and collaborative challenge
Beyond the scientific results, the DESI project has become an example of what can be achieved through international collaboration and cutting-edge technology . By coordinating hundreds of researchers spread across several continents, the consortium has been able to keep the instrument operational almost every night for years, processing an unprecedented avalanche of data.
The system's operation requires the precise integration of the Mayall Telescope's hardware , the mechanics of the positioning robots, the spectrographs' readout electronics, and complex control and analysis software. Each observing session involves planning which regions of the sky will be covered, adjusting the fiber optic pointing, correcting for atmospheric effects, and verifying the quality of the resulting spectra.
All this data flow ends up in gigantic catalogs which, once refined, serve as the basis for cosmological studies. The volume of information generated by DESI is so vast that detailed analysis will continue for years, meaning that the most striking results may not yet be available . Many scientific teams in Europe, America, and Asia are already using these databases to test alternative theories of gravity, explore new models of dark matter, and compare different ways of measuring the expansion of the universe.
The DESI experience also sets a precedent for future installations, such as new optical and radio surveys being planned at different observatories around the world. In a way, this three-dimensional map of the universe serves as a preview of the next generation of precision surveys that will attempt to unravel the remaining pieces of the cosmic puzzle.
With the largest 3D map of the universe now available, science has an unparalleled tool to revise its own theories. The detailed portrait of how galaxies, quasars, and stars are distributed, coupled with clues that dark energy may not be as constant as previously thought, points to a stage where the model of the cosmos will have to be refined and, perhaps, significantly changed. Far from offering definitive answers, DESI's work confirms that the further we look, the more complex and surprising the universe we are trying to understand becomes.
