Researchers from the University of St Andrews have been involved in one of the most extensive surveys of the cosmos conducted, producing the largest high-resolution 3D map of the universe ever made.
The Dark Energy Spectroscopic Instrument (DESI), a five-year survey of the sky, finished ahead of schedule and with vastly more data than expected to create the most detailed 3D map of the universe.
The international team of researchers led by the used the newly created 3D map of the universe to explore dark energy, the fundamental ingredient that makes up about 70% of our universe and is driving its accelerating expansion. By comparing how galaxies clustered in the past with their distribution today, researchers have traced dark energy's influence over 11 billion years of cosmic history.
The international experiment, led by the University of California, Berkeley brings together the expertise of more than 900 researchers (including 300 PhD students) from over 70 institutions, including St Andrews.
DESI began collecting data in May 2021. Since then, the instrument has far surpassed the collaboration's original goals. The plan was to capture light from 34 million galaxies and quasars (extremely distant yet bright objects with black holes at their cores) over the five-year sky survey. DESI instead observed more than 47 million galaxies and quasars and 20 million stars.
DESI is continuing observations and will extend its map to cover more of the sky to better study dark energy as well as dark matter and the evolution of galaxies over time.
Surprising results using DESI's first three years of data hinted that dark energy, once thought to be a "cosmological constant," might be evolving over time. With the full set of five years of data, researchers will have significantly more information to test whether that hint disappears or grows. If confirmed, it would mark a major shift in how we think about our universe and its potential fate, which hinges on the balance between matter and dark energy.
Rita Tojeiro, Professor of Astronomy at the University of St Andrews who has been heavily involved with the project for over a decade, said: "There is no doubt of the huge impact that DESI is having on cosmology. What is also fantastic about DESI, in addition to being a revolutionary cosmology survey, is that this new three-dimensional map is enabling world-class legacy science. Each of the 47 million galaxies and quasars that DESI observed tells a unique story. We can collect these individual stories to reveal the overarching narratives of how galaxies form and evolve through cosmic time. Because DESI is revealing the three-dimensional cosmic web in which galaxies live with unprecedented detail, we can now study how galaxies respond to cosmic structures around them in ways that have not been possible before."
DESI has now measured data for six times as many galaxies and quasars as all previous measurements combined. The collaboration will immediately begin processing the completed dataset, with the first dark energy results from DESI's full five-year survey expected in 2027. In the meantime, DESI scientists continue to analyse the survey's first three years of data, refining dark energy measurements and producing additional results on the structure and evolution of the universe.
DESI will continue observations until the end of 2028 and the extended map will cover parts of the sky that are more challenging to observe: areas that are closer to the plane of the Milky Way, where bright nearby stars can make it harder to see more distant objects, or further to the south, where the telescope must account for peering through more of Earth's atmosphere.
The experiment will also revisit the existing area of the map to collect data from a new set of galaxies: more distant and fainter "luminous red galaxies." These will provide an even denser and more detailed map in the regions DESI has already covered, giving researchers a clearer picture of the universe's history and that of galaxies within.
Professor Tojeiro added: "I have been waiting for over 10 years for this cosmic map. Now it is here and we are lucky enough to extend it and make it even better. The level of detail is incredible, and the map is so rich with information! We will be exploring it for 10 years to come."
Researchers will also study nearby dwarf galaxies and stellar streams, bands of stars torn from smaller galaxies by the Milky Way's gravity. The hope is to better understand dark matter, the invisible form of matter that accounts for most of the mass in the universe but has never been directly detected.
Category Research
