Researchers unveil the largest 3D map of the universe ever made

The Dark Energy Spectroscopic Instrument project, an international collaboration of more than 900 researchers from over 70 institutions around the world including EPFL, has released its first results – a map of galaxies and quasars with unprecedented detail, creating the largest 3D map of the universe ever made.

Traveling back in time

With 5,000 tiny robots installed on the Mayall telescope at Kitt Peak National Observatory in the United States, researchers can look up to 11 billion years into the past. And, this is the first time that scientists have measured the expansion history of that distant period (8-11 billion years) with a precision of better than 1%. The new map surpasses all previous 3D spectroscopic maps combined and confirms the basics of our best model of the universe.

The light from far-flung objects in space has just reached the Dark Energy Spectroscopic Instrument, enabling us to map our cosmos as it was in its youth and trace its growth to what we see today. Understanding how our universe has evolved is tied to how it ends, and to one of the biggest mysteries in physics: dark energy, the unknown ingredient causing our universe to expand faster and faster.

Now, researchers have shared the analysis of their first year of collected data in multiple papers available publicly

“We’re incredibly proud of the data, which have produced world-leading cosmology results and are the first to come out of the new generation of dark energy experiments,” said Michael Levi, DESI director and a scientist at the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which manages the project. “So far, we’re seeing basic agreement with our best model of the universe, but we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving with time. Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon.”

EPFL scientists contributed to DESI in the development of the survey’s targeting strategy (deciding which of the galaxies will be observed), as well as through the development of the robotic fiber-positioner system, including tilt-verification tests on some DESI positioners to validate their performance. The latter was conducted as part of the interdisciplinary "Astrobots" group, which includes EPFL’s Laboratory of Astrophysics (LASTRO), as well as Mohamed Bouri and Denis Gillet’s teams from the School of Engineering.

A group of young scientists from the LASTRO has also been heavily involved in interpreting the enormous amount of data coming in from DESI by characterizing their physical meaning through the construction of advanced numerical modeling and the simulation of our Universe.

"The first-year DESI observation with more than 6 million galaxies and quasars will outperform the previous 2-decadal SDSS surveys. To make full use of this excellent dataset, we need detailed investigation on observational artefacts that prevent us from getting accurate cosmological parameters," explains Jiaxi Yu a PhD student at LASTRO and lead author of one of the papers just released. “Interpreting the observational data requires making thousands of digital twin universes in order to validate and quantify the unprecedented precision of our measurements,” added Daniel Forero-Sanchez, another PhD student at LASTRO.

“It’s incredible to be contributing to this global project that is collecting data from more than a million galaxies a month,” said EPFL Prof. Jean-Paul Kneib, Head of LASTRO. “We are in the golden era of cosmology, with large-scale surveys ongoing and about to be started, including the Square Kilometer Array of which Switzerland and EPFL are also involved. All of these are helping us to better understand the dynamics of our universe and its content and fundamental properties.”

With only the first year of DESI data, researchers can already measure the expansion history of our universe at seven different slices of cosmic time, each with a precision of 1 to 3%. The team put in a tremendous amount of work to account for instrumental and theoretical modeling intricacies, giving confidence in the robustness of the first results.

DESI’s overall precision on the expansion history across all 11 billion years is 0.5%, and the most distant epoch, covering 8-11 billion years in the past, has a record-setting precision of 0.82%. That measurement of our young universe is incredibly difficult to make. Yet within one year, DESI has become twice as powerful at measuring the expansion history at these early times as its predecessor (the Sloan Digital Sky Survey’s BOSS/eBOSS), which took more than a decade.

State-of-the-art science

DESI is the first spectroscopic experiment to perform a fully “blinded analysis,” which conceals the true result from the scientists to avoid any subconscious confirmation bias. Researchers work in the dark with modified data, writing the code to analyze their findings. Once everything is finalized, they apply their analysis to the original data to reveal the actual answer. DESI’s data will be used to complement future sky surveys and to prepare for a recently recommended upgrade (DESI-II).

The DESI collaboration is honored to be permitted to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.