The survey’s technical performance and cosmic achievements are also helping scientists reveal the secrets of the most powerful sources of light in the universe. DESI scientists will present on the instrument’s performance and early astrophysics results this week at a Berkeley Lab-hosted webinar, CosmoPalooza, which will also feature updates from other leading cosmology experiments.
Though it’s only about 10% through its five-year mission, the Dark Energy Spectroscopic Instrument (DESI) has capped off the first seven months of its survey run by smashing through all previous records for three-dimensional galaxy surveys, creating the largest map of the universe ever.
Klaus Honscheid, DESI co-instrument scientist, DESI leadership team member and professor of physics at Ohio State, will deliver the session’s first paper.
“The goal of DESI is to understand one of the greatest mysteries in science today: Why is the expansion of the universe accelerating?” said Paul Martini, former DESI instrument scientist and professor of astronomy at Ohio State. “We cannot explain cosmic acceleration by the known laws of physics, so the answer to this question will be incredibly exciting, no matter what it is.”
Ohio State astronomers played a major role in DESI’s development and continue to contribute significantly throughout its operation. During its creation, Martini managed the testing and integration of the various pieces of equipment used to construct DESI while Honscheid designed the software that keeps the instrument operating.
DESI is an international science collaboration managed by the Department of Energy’s Lawrence Berkeley National Laboratory with primary funding for construction and operations from DOE’s Office of Science. Housed at Kitt Peak National Observatory in Arizona, DESI’s array of 5,000 fiber-optic robots point at 35 million galaxies throughout the universe to gather and analyze their light to precisely map the galaxies’ distance from Earth.
Additionally, researchers and graduate students from Ohio State’s Center for Cosmology and AstroParticle Physics created software, analyzed data, worked on the fiber-optic positioning system and helped design spectrograph components.
Honscheid and his team ensure the instrument runs smoothly and automatically, ideally without any input during a night’s observing.
“It’s constant work that goes on to make this instrument perform,” Honscheid said. “The feedback I get from the night observers is that the shifts are boring, which I take as a compliment.” That monotonous productivity requires detailed control over each of DESI’s 5,000 robots, ensuring their positions are accurate to within 10 microns.
“Ten microns is tiny,” Honscheid said. “It’s less than the thickness of a human hair. And you have to position each robot to collect the light from galaxies billions of light-years away. Every time I think about this system, I wonder, ‘How could we possibly pull that off?’ The success of DESI as an instrument is something to be very proud of.” That level of accuracy is needed to accomplish the survey’s primary task: collecting detailed color spectrum images of millions of galaxies across more than a third of the entire sky. By breaking down the light from each galaxy into its spectrum of colors, DESI can determine how much the light has been redshifted — stretched out toward the red end of the spectrum by the expansion of the universe during the billions of years it traveled before reaching Earth.
The more redshifted a galaxy’s spectrum is, in general, the farther away it is. With a 3D map of the cosmos in hand, physicists can chart clusters and superclusters of galaxies. Those structures carry echoes of their initial formation, when they were just ripples in the infant cosmos. By teasing out those echoes, physicists can use DESI’s data to determine the expansion history of the universe. “There is a lot of beauty to it,” says Berkeley Lab scientist Julien Guy, a co-project scientist for DESI who also serves as a member of the DESI leadership team.
As the universe expands, more dark energy pops into existence, which speeds up the expansion more. This acceleration, researchers believe, is critical in impacting the future of the universe. Finding the answers means learning more about how dark energy’s past behavior — and that’s exactly what DESI is designed to do. Understanding the fate of the universe will have to wait until DESI has completed more of its survey. In the meantime, DESI is already driving breakthroughs in understanding the distant past, more than 10 billion years ago when galaxies were still young.
Understanding the expansion history is crucial to learning more about how dark energy will influence the fate of the universe. Today, about 70% of the content of the universe is dark energy, a mysterious form of energy that accelerates the expansion of the universe. “In the distribution of the galaxies in the 3D map, there are huge clusters, filaments and voids. They’re the biggest structures in the universe. But within them, you find an imprint of the very early universe, and the history of its expansion since then.”
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