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Durham researchers are part of an international collaboration that has completed the most detailed 3D map of the Universe to date.
The mission has delivered an unprecedented dataset that will help scientists test what is driving the cosmos to expand faster over time.
The map comes from the Dark Energy Spectroscopic Instrument (DESI) mounted on the Mayall telescope in Arizona, USA. Astronomers used it to carry out the largest survey of the cosmos to date.
The project has now completed the observations planned for its original five-year mission.
A five-year survey - completed early
DESI is installed at the Kitt Peak National Observatory in Arizona, USA. The collaboration includes 75 institutions across 13 countries and involves hundreds of scientists.
The five-year survey finished ahead of schedule - and delivered vastly more measurements than the team originally anticipated.
In total, researchers measured more than 47 million galaxies and quasars, as well as more than 20 million nearby stars that help reveal the structure of the Milky Way.
Scientists are already using the 3D map to probe dark energy - an unknown cosmic component thought to be responsible for the Universe's accelerating expansion.
In the moment marking the milestone, the instrument's 5,000 fibre-optic "eyes" swivelled to a patch of sky near the Little Dipper, completing the final set of observations for DESI's original mission.
Our researchers are among those leading key parts of the instrument's data capture devices and the analysis of the data
What comes next
DESI will continue observing and extend its map across more of the sky, helping researchers study dark energy as well as dark matter.
By comparing how galaxies clumped together billions of years ago with how they are spread out today, the team can track how the expansion of the Universe has changed.
Results from DESI's first three years of data have already produced a surprising finding: dark energy - until now treated as a fixed "cosmological constant" might be changing over time.
With the full five years of observations now complete, researchers have far more data to test whether that hint fades away - or strengthens. If confirmed, it would reshape how we think the Universe works and what its long-term future could be.
Only 10 years ago I would have thought that measuring the rate at which the universe expands with an accuracy of one percent was just fantasy. Yet, DESI has done it! The amount and quality of the DESI data and the analysis carried out by an international team of very talented scientists has led to this achievement. The rewards are huge: the data suggests an unexpected behaviour of the dark energy that may upturn the currently accepted view of how our universe evolves.
Durham has played a major role in DESI. We designed and built the fibre optic cable system, the 'eyes' of the instrument that channel light from distant objects into the detector.
Our Institute for Computational Cosmology provided huge supercomputer simulations of the evolution of the universe that have been key to interpreting the data.
Durham researcher Willem Elbers lead major parts of the analysis, including the determination of the mass of neutrinos, elementary particles that make up a small fraction of the Universe's dark matter.
