2024-04-14 00:55:13
DESI has created the largest 3D map of our universe to date. The Earth is in the center of this thin slice of the full map. In the magnified section, it is easy to see the basic structure of matter in our universe. Credit: Claire Lemman/DESI collaboration; Custom colormap pack by cmastro
The Dark Energy Spectroscopic Instrument (DESI), mounted on a telescope in Arizona, has created the largest 3D map of the cosmos, mapping more than 30 million galaxies and 3 million quasars. This monumental task, a collaboration of over 900 researchers, helps us understand the expansion of the universe and the role of dark energy.
We now have the largest 3D map of our cosmos ever created, thanks to a powerful instrument mounted atop a telescope in Arizona with a robotic array of 5,000 fiber-optic “eyes” peering into the night sky. Over the past five years, the Dark Energy Spectroscopic Instrument – known in science circles as DESI – has measured the spectra of more than 30 million galaxies and 3 million quasars to determine how fast the universe has been expanding over 11 billion years.
DESI’s announcement is the result of an ongoing international collaboration involving more than 900 researchers from more than 70 institutions, including astronomers at UC Santa Cruz with leadership roles in the project.
And yet, as big as this news is, they say it’s just the beginning.
The Dark Energy Spectroscopic Instrument (DESI) is mounted on the US National Science Foundation’s Nicholas U. Mayall 4-meter Telescope at Kit Peak National Observatory. Credit: KPNO/NOIRLab/NSF/AURA/P. Mernfeld
Pioneering discoveries and future visions
“If the trends hinted at here in this first-year data set are confirmed in our third-year analysis, it will be a major discovery,” said cosmologist Alexi Leoto, associate professor in UC Santa Cruz’s Department of Astronomy and Astrophysics. “It’s going to be a very exciting time to be part of the DESI collaboration.”
Beginning in July, Leauthaud will serve as a spokeswoman for the effort—which includes the duties of a lead organizer—so she is perfectly positioned to provide updates. Other collaborating professors at the University of Santa Cruz include Connie Roccuzzi and J. Xavier Prochaska, also in astronomy and astrophysics.
Roccuzzi led the commissioning of the instrument at the 4-meter Mayall Telescope at Kit Peak National Observatory, and her current role is as instrument scientist, helping to keep it running in top condition. In addition, the professors pay tribute to a “phenomenal team” of undergraduates, graduate students and postdocs at the University of California who were deeply involved in the project – visiting the telescope in Arizona on a regular basis to help with observations.
Decipher the mysteries of dark energy
As explained in a statement from the Lawrence Berkeley National Laboratory, where DESI is based: “Understanding how our universe evolved is related to how it ends, and to one of the greatest mysteries in physics: dark energy, the unknown component that causes our universe to expand faster and faster.”
This is the first time scientists have measured the expansion history of the young universe with an accuracy of better than 1% – giving us our best view yet of how the universe evolved. Researchers shared their analysis of their first year of collected data in several papers to be published today on arXiv and in talks at a meeting of the American Physical Society in the United States and Rencontres de Moriond in Italy.
In this 360-degree video, take an interactive flight through millions of galaxies mapped using coordinate data from DESI. Credit: Fiske Planetarium, CU Boulder and DESI Collaboration
Sven Heidenreich, a postdoctoral researcher at the University of Santa Cruz, wears multiple hats at DESI: serves on the Early Career Scientists Committee, performs galaxy-by-galaxy measurements with the instrument, and leads a working group that envisions various scenarios for a potential continuation of the DESI mission.
“The goal is to measure how DESI galaxies bend and distort the light from more distant galaxies located behind them, an effect known as gravitational lensing,” said Heidenreich, who spent a week on site at Kitt Peak in late 2023. “These measurements will be crucial for analyzing how galaxies are affected by the distribution of dark matter surrounding them. Therefore, the results will help to improve our understanding of the parameters that describe our current model of the composition of the universe and its evolution.”
11 ton time machine
DESI’s components are designed to automatically pinpoint preselected groups of galaxies, collect their light, then split that light into narrow bands of color to accurately map their distance from Earth and gauge how much the universe expanded as that light traveled to Earth. Under ideal conditions, DESI can pass through a new group of 5,000 galaxies every 20 minutes.
By repeatedly mapping the distance to many millions of galaxies and quasars across a third of the sky over the past five years, DESI is teaching us more about dark energy and the history of the universe. Our current understanding is that gravity slowed the rate of expansion in the early universe, but since then dark energy has accelerated its expansion.
DESI’s overall accuracy in the expansion history over the entire 11 billion years is 0.5%, and the most distant period – covering 8-11 billion years in the past – has a record accuracy of 0.82%. This measurement of our young universe is incredibly difficult. However, within one year, DESI became twice as powerful at measuring the expansion history at these early times than its predecessor (BOSS/eBOSS of the Sloan Digital Sky Survey), which spanned more than a decade.
Looking at the DESI map, it’s easy to see the basic structure of the universe: strands of galaxies clustered together, separated by spaces with fewer objects. Our early universe, far beyond DESI’s view, was quite different: a hot, dense soup of subatomic particles moving too fast to form stable matter like the atoms we know today. Among those particles were hydrogen and helium nuclei, collectively called baryons.
Tiny fluctuations in this early dose of plasma caused pressure waves, moving the bullion into a pattern of ripples similar to what you’d see if you threw a handful of gravel into a pond. As the universe expanded and cooled, neutral atoms formed and the pressure waves stopped, freezing the ripples in three dimensions and increasing the clustering of future galaxies in the dense regions. Billions of years later, we can still see this faint pattern of three-dimensional ripples, or bubbles, in the characteristic separation of galaxies—a feature called baryon acoustic oscillations (BAOs).
This animation shows how acoustic oscillations in the baryon act as a cosmic ruler to measure the expansion of the universe. Credit: Claire Lemman/DESI and the Jenny Nuss Lab/Berkeley collaboration
Researchers use BAO measurements as a cosmic ruler. By measuring the apparent size of these bubbles, they can determine distances to the material responsible for this faintest pattern in the sky. Mapping the BAO bubbles both near and far allows researchers to slice the data into chunks, measure how fast the universe expanded each time in its past, and model how dark energy affects that expansion.
“We measured the expansion history over this vast span of cosmic time with a precision that exceeds all previous BAO surveys combined,” said Hee-Jong Seo, a professor at Ohio State University and co-leader of DESI’s BAO analysis. “We are very excited to learn how these new measurements will improve and change our understanding of the cosmos. Humans have an eternal fascination with our universe, they also want to know what it is made of and what will happen to it.”
For more information on these results, see Dark energy revealed through the largest 3D map of the universe ever created.
DESI is supported by the DOE Office of Science and by the National Center for Scientific Computing for Energy Research, a DOE Office of Science User Facility. Additional support for DESI is provided by the US National Science Foundation; the UK Science and Technology Facilities Council; the Gordon and Betty Moore Foundation; the Heising-Simon Foundation; the French Commission for Alternative Energies and Atomic Energy (CEA); the National Council for the Humanities, Sciences and Technologies of Mexico ; the Ministry of Science and Innovation of Spain; and by the DESI member institutions.
The DESI Collaboration is honored to be authorized to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain of special importance to the Tohono O’odham Nation.
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