dark energy spectrophotometerDESI) finished the first seven months of his research by breaking all previous records for 3D galaxy surveys, creating the largest and most detailed map of the universe ever made. However, it only approaches 10% of the way during its five-year mission. Once complete, this enormously detailed 3D map will provide a better understanding of dark energy, giving physicists and astronomers a better understanding of the universe’s past and future. Meanwhile, the remarkable engineering and cosmic achievements of research so far are helping scientists to unravel the secrets of the most powerful sources of light in the universe.
DESI is an international scientific collaboration managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Laboratory) with core construction and operations funding from the Department of Energy’s Office of Science.
DESI scientists will present the instrument’s performance and some early astrophysical results this week during a webinar hosted by Berkeley Lab called CosmoPalooza, which will also feature updates from other groundbreaking cosmic experiments.
“There’s a lot of beauty in it,” said Julian Gay, a Berkeley Lab scientist, one of the speakers. “In the distribution of galaxies on the 3D map, there are huge clusters, filaments and voids. They are the largest structures in the universe. But in it you will find an imprint of the very early universe and the history of its expansion since then.”
DESI has come a long way to get to this point. Originally proposed more than a decade ago, construction of the device began in 2015. It is installed at the 4-meter Kitt Peak National Observatory Nicholas U. Mayall Telescope near Tucson, Arizona. Kitt Peak National Observatory is a program of NOIRLab of the National Science Foundation (NSF), which the Department of Energy contracted to operate the Mayall Telescope for the DESI study. The instrument first saw light at the end of 2019. Then, during the verification phase, the coronavirus pandemic hit, and the telescope shut down for several months, though some continued to work remotely. In December 2020, DESI again turned its sights to the sky to test its hardware and software, and by May 2021 it was ready to begin its scientific research.
Part of a 3D map of galaxies from the completed Sloan Digital Sky Survey.
A cross-section across the 3D map of galaxies from the first few months of the Dark Energy Spectroscopy (DESI; right). Earth is in the center, and the most distant galaxies are more than 10 billion light-years away. Each point represents a galaxy. This 2D slice of the 3D DESI map shows only about 800,000 of the 7.5 million galaxies currently scanned, which by itself is just a fraction of the 35 million galaxies that will be on the final map. Credit: D. Schlegel/Berkeley Lab using data from DESI
But work on DESI itself did not stop when the investigation began. “It’s a work in progress to keep this instrument performing,” said Ohio State University physicist Klaus Hünscheid, instrument scientist involved in the project, who will present the first paper from the CosmoPalooza DESI session. Honscheid and his team ensure that the machine runs smoothly and automatically, ideally without any input during nighttime monitoring. “The feedback I get from night watchers is that shifts are boring, which I take as a compliment,” he said.
But this monotonous throughput requires incredibly detailed control of each of the 5,000 advanced robots that place optical fibers on the DESI instrument, ensuring that their positions are accurate to within 10 microns. “Ten tiny microns,” Hunchhead said. “It’s less than the thickness of a human hair. And you have to position each robot to collect light from galaxies that are billions of light years away. Every time I think about this system, I wonder how we can achieve it? DESI’s success as a tool is something to be proud of.”
Seeing the true colors of dark energy
This level of accurately It is required to accomplish the primary task of the research: to collect detailed color-spectral images of millions of galaxies over a third of the entire sky. By separating the light from each galaxy into their color spectrum, DESI can determine how much light turns red — stretched toward the red end of the spectrum by the expansion of the universe over the billions of years it traveled before reaching Earth. It is these redshifts that show the DESI depth of sky.
The greater the redshift of a galaxy’s spectrum in general, the further away it is from it. With a 3D map of the universe in hand, physicists can map galaxy clusters and giant clusters. Those structures bear echoes of their original composition, when they were just ripples in the universe of childhood. By triggering these echoes, physicists can use DESI data to determine the expansion history of the universe.
The new quasar discovered with DESI gives a glimpse of the universe as it was nearly 13 billion years ago, less than a billion years after the Big Bang. This is the most distant quasar detected so far with DESI, among a selection of very high redshift quasars from DESI. The background shows this quasar and its environment in the DESI Legacy Photogrammetry Surveys. Credit: Jenny Yang, Steward Observatory/University of Arizona
Our scientific goal is to trace the imprint of waves in the primordial plasmaDude said. “It’s amazing that we can detect the effect of these waves after billions of years, and so quickly, in our research.”
Understanding the history of expansion is crucial, as nothing less than the fate of the entire universe is at stake. Today, about 70% of the universe’s contents are made up of dark energy, a mysterious form of energy that’s pushing the universe’s expansion faster. As the universe expands, more dark energy is created, accelerating the expansion, in a cycle that pushes the dark energy portion of the universe higher than ever before. Dark energy will ultimately determine the fate of the universe: will it expand forever? Will it collapse on its own again in no time? the great explosion Alternative method? Or will she tear herself up? Answering these questions means learning more about how dark energy behaved in the past – which is exactly what DESI was designed for. By comparing the history of expansion with the history of growth, cosmologists can determine whether Einstein’s general theory of relativity applies to these vast stretches of space and time.
Black holes and bright galaxies
But understanding the fate of the universe will have to wait until DESI completes more of its research. Meanwhile, DESI is already making breakthroughs in our understanding of the distant past, more than 10 billion years ago, when galaxies were still young.
“It’s really amazing,” said Ragadeepika Pucha, a University of Arizona graduate student in astronomy who works at DESI. “DESI will tell us more about the physics of galaxy formation and evolution.”
Pucha and her colleagues use DESI data to understand the behavior of medium-mass black holes in small galaxies. Supermassive black holes are believed to inhabit the heart of nearly every major galaxy, including our own Milky Way. But whether or not small galaxies always have (smaller) black holes at their cores. Black holes are almost impossible to find on their own, but if they attract enough material, they will become easier to detect. When gas, dust and other materials enter into Black hole Heating on its way inland (to temperatures above the star’s core), an active galactic nucleus (AGN) forms. In large galaxies, active galactic nuclei are among the brightest objects in the known universe. But in smaller galaxies, AGNs can be fainter and hard to distinguish from newborn stars. The spectra created by DESI could help solve this problem – and the wide range in the sky will provide more information about the cores of young galaxies than ever before. These cores, in turn, will provide scientists with clues as to how AGNs formed in the early universe.
Quasars – a diverse group of bright galaxies – are among the brightest and most distant objects. “I like to think of them as lampposts, given the past in the history of the universe,” said Victoria Fawcett, a graduate student in astronomy at Durham University in the UK. Quasars are excellent probes of the early universe because of their enormous power. DESI data goes back 11 billion years.
Fawcett and her colleagues use DESI data to understand the evolution of quasars themselves. Initially, quasars were thought to be surrounded by an envelope of dust, making the light they emit red, like the sun through fog. As they age, they expel this dust and turn blue. But this theory has been difficult to test, due to the lack of data on red quasars. DESI changed that by finding more quasars than any previous study, with 2.4 million expected in the final study data.
“DESI is really great because it picks up things that are fainter and redder,” says Fawcett. She adds that this allows scientists to test ideas about the evolution of quasars that could not be tested before. And this is not just limited to quasars. “We’re finding quite a few exotic systems, including large samples of rare things that we haven’t been able to study in detail before,” Fawcett said.
There is more to come DESI. The research has already cataloged more than 7.5 million galaxies and is adding more at a rate of over a million per month. In November 2021 alone, DESI cataloged the redshifts of 2.5 million galaxies. By the end of its operation in 2026, DESI is expected to have more than 35 million galaxies in its catalog, illuminating a wealth of cosmological and astrophysical research.
“All of this data is just there and waiting to be analyzed,” Bucha says. “And then we’ll find a lot of amazing things about galaxies. That’s exciting to me.”
DESI is supported by the Department of Energy’s Office of Science and the National Center for Scientific Computing for Energy Research, a user facility of the Department of Energy’s Office of Science. 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-Simons Foundation, the French Commission for Alternative and Atomic Energy (CEA), the National Science and Technology Council of Mexico, and the Spanish Ministry of Economy and DESI member institutions.
The DESI Partnership is honored to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain of particular interest to the nation of Tohono O’odham.
