New Delhi: The Dark Energy Spectroscopic Instrument (DESI) has completed its planned five-year survey, and has produced the largest, high-resolution three-dimensional map of the Universe till date, mapping over 47 million galaxies and quasars. The instrument is mounted on the Nocholas U Mayall 4-metre telescope at Kitt Peak National Observatory in Arizona, operated by the US National Science Foundation (NSF). All the observations planned for its original 14,000-square-degree map was completed ahead of schedule, on 15 April 2026. The survey gathered six times as many cosmological targets as all the previous surveys combined, and also observed 20 million stars.

Scientists will use the map to measure dark energy, which constitutes about 70 per cent of the Universe, and drives its accelerating expansion. The researchers can compare the clustering of galaxies from the present time or the local universe, back to 11 billion years. The data can test whether dark energy has remained a constant or has evolved over time. Early results from the first three years already hinted at the possible evolution of dark energy, raising questions on the long-term fate of the Universe. Analysis of the full five-year dataset is expected to deliver refined dark energy measurements by 2027.

DESI continues to observe the Universe

The DESI project began collecting data in May 2021, and exceeded its original goal of mapping 34 million galaxies and quasars, despite the challenges introduced by the COVID-19 pandemic, fires in 2022, and subsequent heavy rains. Because of the strong performance of the instrument, DESI will continue observations through 2028 as part of an extended survey, that is expected to increase the map by 20 per cent, to 17,000 square degrees. This extended survey will also cover harder-to-observe regions near the plane of the Milky Way. The survey will also revisit existing target areas to observe fainter, more distant luminous red galaxies, and study nearby dwarf galaxies and stellar streams as well. Processing of the complete dataset has commenced, with additional science results expected in the future.