dark energy spectroscopy instrumentDESI) has capped the first seven months of its survey by smashing all previous records of 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 completed, this massively detailed 3D map will produce a better understanding of dark energy, thus giving physicists and astronomers a better understanding of the universe’s past and future. Meanwhile, the amazing technical performance and cosmic achievements of the survey so far are helping scientists to reveal the secrets of the most powerful sources of light in the universe.
DESI is an international science collaboration managed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Laboratory) with seed funding for construction and operations from the Department of Energy’s Office of Science.
DESI scientists are presenting the instrument’s performance, and some early astrophysics results, this week at a webinar hosted by Berkeley Lab called CosmoPalooza, which will also feature updates from other pioneering cosmological 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 in the 3D map, there are massive clusters, filaments, and voids. They are the largest structures in the universe. But within them, you 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. It was originally proposed more than a decade ago, and construction of the device began in 2015. It is installed in the 4-meter Nicholas U Maywell Telescope at Kate Summit Observatory near Tucson, Arizona. Kitt Peak National Observatory is a program of the National Science Foundation (NSF) NOIRLab, which the Department of Energy contracts to operate the Mayall Telescope for the DESI survey. The instrument saw its first light in late 2019. Then, during its validation phase, the coronavirus pandemic hit, and the telescope shut down for several months, although some remote work continued. In December 2020, DESI turned its sights to the sky again, tested its hardware and software, and by May 2021 was ready to begin its scientific survey.
But work on DESI itself was not finished once the survey began. “It’s work in progress to get this tool to work,” said Ohio State University physicist Klaus Hünscheid, a machine scientist involved in the project, who will present the first paper from the CosmoPalooza DESI session. Honscheid and his team ensure that the tool runs smoothly and automatically, ideally without any interference during nighttime monitoring. “The feedback I get from night watchers is that shifts are boring, and I take it as a compliment,” he said.
But this monotonous throughput requires incredibly detailed control of each of the 5,000 sophisticated robots that place the optical fibers on the DESI instrument, ensuring that their positions are accurate to within 10 microns. “Ten microns is very small,” Honshed said. “It’s less than the thickness of a human hair. And you have to put each robot in to collect light from galaxies that are billions of light years away. Every time I think of 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 health It is required to accomplish the primary mission of the survey: to collect detailed color spectrum images of millions of galaxies across more than a third of the entire sky. By breaking up the light from each galaxy into their color spectrum, DESI can quantify the redshift of the light — 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 make DESI see the depth of the sky.
The greater the redshift of the galaxy’s spectrum in general, the further away it is from it. With a 3D map of the universe in hand, physicists can map clusters and superclusters of galaxies. Those structures bear echoes of their initial formation, when they were just ripples in the infant universe. By triggering these echoes, physicists can use DESI data to determine the expansion history of the universe.
Our scientific goal is to measure the fingerprint of waves in the primordial plasmaGuy said. “It’s amazing that we can actually detect the effect of these waves after billions of years, and so quickly in our survey.”
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 content is dark energy, a mysterious form of energy that’s driving the universe’s expansion faster. As the universe expands, more dark energy appears, accelerating the expansion further, in a cycle that drives a portion of the dark energy in the universe upward. Dark energy will ultimately determine the fate of the universe: will it expand forever? Will he collapse in on himself again, in the great explosion backwards? Or will she tear herself up? Answering these questions means learning more about how dark energy behaved in the past – and that’s exactly what DESI was designed for. And by comparing the history of expansion with the history of growth, cosmologists can verify whether Einstein’s theory of general relativity holds up over these enormous stretches of space and time.
Black holes and bright galaxies
But understanding the fate of the universe must wait until DESI completes more of its survey. Meanwhile, DESI is already driving 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 working on 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 thought to inhabit the heart of nearly every large galaxy, such as ours Milky Way. But whether or not small galaxies always have their own (smaller) black holes in their nuclei. Black holes would be nearly impossible to find on their own – but if they attract enough material, they will become easier to detect. When gas, dust and other materials fall into Black hole As it warms (to temperatures above the star’s core) on its way inland, 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 much fainter, and hard to distinguish from newborn stars. The spectra captured by DESI could help solve this problem — and how far they spread across the sky will give more information about the cores of young galaxies than ever before. These cores, in turn, will give scientists clues about 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, looking back at 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 sheer power. DESI data will go back in time 11 billion years.
Fawcett and her colleagues use DESI data to understand the evolution of quasars themselves. Quasars are thought to begin surrounded by an envelope of dust, which reddens the light they emit, like the sun through haze. As they age, they expel this dust and become bluer. But this theory has been difficult to test, due to the paucity of data on red quasars. DESI changes that, as more quasars have been found than any previous survey, with 2.4 million quasars expected in the final survey data.
“DESI is really great because it picks up things that are fainter and redder,” Fawcett said. 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 find a very large number of exotic systems, including large samples of rare things that we have not been able to study in detail before,” Fawcett said.
There is more to come DESI. The survey has already cataloged more than 7.5 million galaxies and is adding more at a rate of over a million galaxies 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, enabling a vast array of cosmology and astrophysics research.
“All of this data is just there, and it’s just waiting to be analyzed,” Bucha said. “And then we’ll find a lot of amazing things about galaxies. To me, that’s exciting.”
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, the Ministry of Spanish Economy, DESI member institutions.
DESI Collaboration has the honor to allow him to conduct scientific research on Mount Iolkam Du’ag (Kitt Peak), a mountain of particular interest to the nation of Tohono O’odham.