The Dark Energy Spectroscopic Instrument (DESI) has reached a defining milestone in modern cosmology, completing its original five-year survey and delivering the most detailed map of the Universe ever constructed.
Operating from the Kitt Peak National Observatory in Arizona, DESI has charted more than 47 million galaxies and quasars in three dimensions.
The result is a high-resolution cosmic map that stretches across billions of years, offering scientists an unprecedented dataset to probe how the Universe has evolved.
Originally scheduled to run through a five-year mission, the project exceeded expectations both in speed and scale.
Its success has now secured an extension through 2028, with plans to expand and refine this already vast map of the Universe.
How DESI mapped the cosmos
On April 15, DESI quietly marked the completion of its primary survey.
Its 5,000 fibre-optic “eyes” scanned a region near the Little Dipper, repeatedly locking onto distant sources of light. Each observation captured photons that had travelled for billions of years before reaching Earth.
At the heart of DESI is a highly coordinated system. Robotic positioners align optical fibres with extreme precision – down to less than the width of a human hair – while spectrographs split incoming light into its component wavelengths.
This allows researchers to determine the distance, motion and composition of each observed object.
Every night, around 80 gigabytes of data are transmitted to supercomputers for processing. This continuous pipeline enables near real-time analysis and adjustments, ensuring the survey remains efficient and accurate.
A map that reshapes our understanding
The newly completed map of the Universe is not just a visual achievement – it is a scientific tool designed to tackle one of physics’ biggest questions: the nature of dark energy.
Dark energy is believed to make up roughly 70% of the Universe and is responsible for its accelerating expansion.
By comparing how galaxies cluster today with how they were distributed billions of years ago, DESI allows scientists to track how this mysterious force has behaved over 11 billion years of cosmic history.
Early analysis from the first three years of data hinted at something unexpected. Dark energy, long assumed to be constant, may actually evolve over time. With the full five-year dataset now complete, researchers will test whether this signal strengthens or disappears.
If confirmed, the implications would be profound. It would challenge the standard cosmological model and reshape predictions about the ultimate fate of the Universe.
A global scientific effort
DESI is not a single-institution project. It brings together more than 900 researchers from over 70 institutions worldwide, including hundreds of doctoral students.
The experiment is led by the Lawrence Berkeley National Laboratory and funded by the Department of Energy’s Office of Science. It operates on the Nicholas U. Mayall Telescope, a key instrument for wide-field astronomical surveys.
Despite facing significant obstacles, including pandemic-related disruptions during final testing and the 2022 Contreras Fire that swept across Kitt Peak, the project not only continued but exceeded its initial targets.
Surpassing expectations
DESI’s original goal was to measure 34 million galaxies and quasars. Instead, it catalogued over 47 million, along with an additional 20 million stars. This means the survey has collected six times more cosmological data than all previous efforts combined.
Efficiency gains played a major role. Improvements in software, observing strategies, and instrument performance allowed the team to complete additional passes of the sky.
The survey ultimately covered about two-thirds of the northern sky, with multiple overlapping scans to improve data quality.
These optimisations also enabled a parallel “Bright-Time Survey,” conducted when moonlight would otherwise limit observations of faint objects.
What comes next for the map of the Universe
The project’s extension through 2028 will expand the map of the Universe even further.
Coverage will grow from 14,000 to 17,000 square degrees, pushing into more challenging regions of the sky, including areas near the Milky Way’s dense stellar plane and farther southward views through thicker layers of Earth’s atmosphere.
DESI will also revisit previously mapped regions, focusing on fainter and more distant galaxies – particularly luminous red galaxies. This will create an even denser and more detailed cosmic map, improving measurements of large-scale structure.
Beyond dark energy, researchers will use the expanded dataset to investigate dark matter by studying nearby dwarf galaxies and stellar streams – remnants of smaller galaxies torn apart by gravitational forces.
A dataset still yielding discoveries
While the full five-year dataset is now complete, analysis is just beginning. Scientists are continuing to refine results from the first three years, with additional studies on cosmic structure and evolution expected in the near term.
The first major dark energy findings from the full dataset are anticipated in 2027.
In parallel, new observations for the extended survey are already underway, integrated seamlessly into DESI’s nightly operations to maximise efficiency.
A new era in cosmic cartography
The completion of DESI’s initial survey marks a turning point in how scientists construct and use a map of the Universe.
With its scale, precision, and depth, the dataset provides a foundation for answering some of the most fundamental questions in cosmology.
And with years of observations still ahead, that map is only getting bigger.