An international team co-led by Ohio University physics professor Hee-Jong Seo is tracking ripples from relic cosmic sounds spanning 11 billion years of the universe's history with unprecedented precision.
With 5,000 small robots in a mountaintop telescope, researchers can see 11 billion years into the past. Light from distant objects in the universe is just now reaching the Dark Energy Spectroscopy Instrument (DESI), allowing us to map the universe as it was in its youth to what we see today. growth can be tracked. Understanding how our universe has evolved can help us understand how the universe will end, and one of the biggest mysteries in physics: the unknown ingredients that are accelerating the rate of expansion of the universe. It is associated with a certain dark energy.
To study the effects of dark energy over the past 11 billion years, DESI used the most accurate measurements to date to create the largest 3D map of the universe ever constructed. This is the first time scientists have measured the expansion history of the young Universe to better than 1% accuracy, giving us the best view yet of how the Universe evolved. The researchers shared their analysis of the data they collected during his first year in multiple papers published on arXiv and in talks at the American Physical Society conference in the US and at his Rencontres de Moriond in Italy. .
“We are extremely proud of the first data from a new generation of dark energy experiments, producing world-leading cosmology results,” said Michael, Department of Energy Lawrence scientist and DESI director.・Levi said. Berkeley National Laboratory manages the project. “So far we've seen basic agreement with the best models of the universe, but we've also seen some interesting differences that could indicate that dark energy is evolving over time. These may or may not be resolved as more data becomes available, so we look forward to beginning our analysis of the three-year dataset soon.”
The primary model of our universe is known as the Lambda CDM. This includes both weakly interacting types of matter (cold dark matter, or CDM) and dark energy (lambda). Both matter and dark energy shape how the universe expands, but in opposite ways. Matter and dark matter slow expansion, while dark energy accelerates expansion. The amount of each influences how our universe evolves. This model nicely explains the results of previous experiments and what the universe looks like over time.
“No spectroscopic experiment has ever obtained this much data, and we continue to collect data from more than 1 million galaxies each month,” said Berkeley Lab scientist and co-spokesperson for the experiment. said Nathalie Palanque-Delabreuil. “It's amazing that with just one year of data, we can already measure the expansion history of the universe at seven different slices of cosmic time, each with an accuracy of 1 to 3 percent. We put a lot of effort into accounting for the complexity of the modeling, which gives us confidence in the robustness of our initial results.”
DESI's overall accuracy for all 11 billion years of expansion history is 0.5%, and it has a record accuracy of 0.82% for the most distant era, covering the past 8-11 billion years. Measuring our young universe is incredibly difficult. But within his year, DESI became twice as powerful in its ability to measure this early expansion history compared to its predecessor (his BOSS/eBOSS at Sloan Digital Sky Survey), which took more than a decade. .
“We are pleased to see the cosmology results from DESI's first year of operation,” said Gina Lameika, DOE's Associate Director for High Energy Physics. “DESI continues to amaze us with its impressive performance. “It's already shaping our understanding of the universe.”
A trip back in time
DESI is an international collaboration of more than 900 researchers from more than 70 institutions around the world. The instrument was built and operated with funding from his DOE Office of Science and is a program of his NOIRLab at NSF, the National Science Foundation's Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory. is installed at the top of the.
Looking at the DESI map makes it easy to understand the fundamental structure of the universe. Bundles of galaxies cluster together and are separated by voids containing fewer objects. Far beyond the DESI view, our very early universe was quite different. The hot, thick soup of subatomic particles moved too quickly to form stable matter like the atoms we know today. Among those particles were hydrogen and helium nuclei, collectively called baryons.
Small fluctuations in this nascent ionized plasma caused pressure waves that moved the baryons into a ripple pattern. This is similar to what you would see if you threw a handful of gravel into a pond. As the universe expanded and cooled, neutral atoms were formed, pressure waves stopped, three-dimensional ripples froze, and future clusters of galaxies in dense regions increased. Billions of years later, you can still see this faint 3D ripple or bubble pattern in the characteristic separations of galaxies. This is a feature called baryon acoustic oscillations (BAO).
Researchers use BAO measurements as a cosmic ruler. By measuring the apparent size of these bubbles, we can determine the distance to the material responsible for this very faint pattern in the sky. By mapping BAO's bubbles near and far, researchers can slice the data into chunks and measure how fast the universe was expanding at each point in the past, allowing dark energy to You can model how it affects expansion.
“We measured the history of expansion over this vast cosmic time with greater precision than all previous BAO surveys combined,” said Hee-jung Seo, a professor at Ohio University and co-leader of DESI's BAO analysis. he said. “We are very excited to learn how these new measurements will improve and change our understanding of the universe. We want to know what it’s made of and what happens to the universe.”
David Valsin, a postdoctoral researcher at Ohio University, is collaborating with Seo. The two co-authored several papers analyzing his DESI data. Seo's second-year graduate student, Jaide Swanson, is also a co-author on BAO's main alphabet paper.
Using galaxies to measure their expansion history to better understand dark energy is a technology, but it has limitations. At some point, the light from a typical galaxy is too weak, so researchers focus on quasars, very distant bright galactic nuclei with black holes at their centers. Because light from quasars is absorbed as it passes through intergalactic gas clouds, researchers can map pockets of dense matter and use them in the same way they use galaxies. This is a technique known as using a “Lyman Alpha Forest.”
Researchers extended BAO measurements to the past 11 billion years using 450,000 quasars, the largest set ever collected for Lyman Alpha forest measurements. By the end of the survey, DESI plans to map 3 million quasars and 37 million galaxies.
cutting edge science
DESI is the first spectroscopic experiment to perform a completely “blind analysis” that hides the true results from scientists to avoid subconscious confirmation bias. Researchers work in the dark on the modified data and write code to analyze the results. Once everything is done, apply the analysis to the original data to reveal the actual answer.
“The analytical methods we used give us confidence in our results, particularly in showing that Lyman-alpha forests are a powerful tool for measuring the expansion of the universe,” Berkeley Lab said. said Julian Guy, a scientist and co-principal investigator. Process the information from the DESI spectrometer. “The data set we are collecting is extraordinary, as is the rate of collection. This is the most accurate measurement I have ever made in my life.”
DESI data will be used to complement future sky surveys such as the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, and to DESI (DESI-II), which is recommended in a recent report in US Particle. used to prepare for potential upgrades. Physics project prioritization panel.
“We are in a golden age of cosmology. Large-scale investigations are underway and will begin soon, and new techniques are being developed to make the most of these datasets,” says French Alternative said Arnaud de Mattia, a researcher at the Energy Research Institute. At the Commission on Atomic Energy (CEA), he co-leads the DESI group, which interprets cosmological data. “We are all eager to see whether new data can confirm the features we saw in the first-year samples and give us a deeper understanding of the dynamics of the universe.”
DESI is supported by the DOE Office of Science and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility. Additional support for DESI is provided by the National Science Foundation. UK Science and Technology Facilities Council. Gordon and Betty Moore Foundation. Heising-Simons Foundation. French Alternative Energy and Atomic Energy Commission (CEA). Mexican National Council for Humanities and Technology. Spanish Ministry of Science and Innovation. By DESI member institutions.
The DESI Collaborative is honored to have been granted permission to conduct scientific research on Iorcum Duag (Kitt Peak), a mountain of special significance to the Tohono O'odham Nation.