Largest-ever 3D map of the universe lets us travel back 11 billion years
The Dark Energy Spectroscopic Instrument (DESI) is on a mission to explore dark energy. It maps millions of celestial objects to understand the universe’s accelerating expansion.
The DESI collaboration has now released its first major dataset, making it available to researchers and the public. This dataset includes information on 18.7 million objects, covering 4 million stars, 13.1 million galaxies, and 1.6 million quasars.
DESI’s potential beyond dark energy
While DESI’s main goal is to study dark energy, the new dataset has potential beyond this. It could help scientists understand galaxy evolution, black holes, dark matter, and the Milky Way’s structure.
“DR1 already gave the DESI collaboration hints that we might need to rethink our standard model of cosmology,” said Stephen Bailey, a scientist at Berkeley Lab.
“But these world-class datasets are also valuable for the rest of the astronomy community to test a huge wealth of other ideas, and we’re excited to see the breadth of research that will come out.”
DESI is an international effort with over 900 researchers from more than 70 institutions. Berkeley Lab leads the project, and the instrument is installed on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona.
DESI’s massive dataset
Anyone can access DESI’s data through the National Energy Research Scientific Computing Center (NERSC). Space enthusiasts can also explore DESI’s findings through the interactive Legacy Survey Sky Browser.
The latest release expands on DESI’s Early Data Release, offering ten times as much data and covering a much larger area of the sky. It includes data collected between May 2021 and June 2022, along with earlier validation surveys.
DESI’s observations range from nearby stars to galaxies that are billions of light-years away. Since light takes time to travel, looking deep into space means looking into the past.
This allows DESI to create a timeline of the universe that reaches back 11 billion years.
Breakthrough in 3D mapping
Despite being just a fraction of DESI’s total expected output, this 270-terabyte dataset is remarkable. It provides precise distance measurements for millions of galaxies and contains twice as many extragalactic objects as all previous 3D surveys combined.
Within its first year, DESI became the largest spectroscopic redshift survey ever conducted. It sometimes recorded data on more than 1 million objects in a single month.
By 2024, DESI researchers had used the dataset to create the largest 3D map of the universe.
“The DESI project has maintained the pace of making 3D maps of the universe that are 10 times larger every decade,” said David Schlegel of Berkeley Lab.
“That’s our version of Moore’s Law for cosmology surveys. The rapid advance is powered by the clever combination of improved instrument designs, technologies, and analysis of ever-fainter galaxies.”
DESI captures light from distant galaxies
DESI captures light from distant galaxies using 5,000 fiber-optic “eyes.” Under ideal conditions, the instrument can record data on more than 100,000 galaxies in a single night.
“DESI is unlike any other machine in terms of its ability to observe independent objects simultaneously,” said John Moustakas, a professor at Siena College and co-lead of DR1.
By breaking light into its color spectrum, researchers can measure how much it has shifted toward the red end due to the universe’s expansion.
This information helps scientists determine an object’s distance, which allows DESI to map cosmic history in three dimensions.
High-speed data processing
Each night, DESI transfers its images to supercomputers at NERSC. The facility analyzes the data and sends results back to researchers.
The entire process happens overnight. This system connects data collection and analysis in real time, speeding up discoveries.
“For this data release, we made it so DESI could run on our most advanced supercomputer, Perlmutter,” said Daniel Margala of NERSC.
Perlmutter’s powerful GPUs allow DESI to process data nearly 40 times faster than previous systems. What once took months now takes weeks.
Even though data is processed daily, researchers continually refine their code to extract better results.
When they complete a milestone, like a full year of data collection, they reprocess the entire dataset using the latest improvements. It took about a month to process DR1.
Endless research possibilities
DESI is now in its fourth year of a five-year mission. By the end of the project, it aims to catalog spectra for over 50 million galaxies and quasars.
Scientists hope the dataset will help researchers worldwide, including those without access to large telescopes.
A key part of this release is detailed documentation to help scientists who are unfamiliar with DESI to understand its contents.
“We’re still discovering all the things you can do with this dataset, and we want the community to be able to try out all their creative ideas,” said Anthony Kremin of Berkeley Lab.
“There are endless kinds of interesting science you can do when you combine our data with outside information.”
How to access DESI’s data
The DESI DR1 paper is available on the DESI Data website and will be published on arXiv. Videos discussing the release are on the DESI YouTube channel.
Researchers presented the dataset and the latest dark energy findings at the American Physical Society’s Global Physics Summit in Anaheim, California.
Image Credit: Luke Tyas/Berkeley Lab and KPNO/NOIRLab/NSF/AURA
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