Editor’s note: This press release by the Dark Energy Survey collaboration was originally published by the Institut de Física d’Altes Energies about the constraints on dark energy set by the measurement of baryonic acoustic oscillations.
DES is an international collaboration comprising more than 400 astrophysicists, astronomers and cosmologists from over 25 institutions led by members from the U.S. Department of Energy’s Fermi National Accelerator Laboratory. DES mapped an area almost one-eighth of the entire sky using the Dark Energy Camera, a 570-megapixel digital camera funded by the DOE Office of Science. The result highlights research made possible thanks to the unique observing capabilities of the Dark Energy Camera, which was built and tested at Fermilab for the Dark Energy Survey.
“With the Dark Energy Survey, we can peer back in time and measure the universe’s growth with unprecedented accuracy. We are reaching farther into the past than other galaxy surveys,” said DES director and spokesperson Rich Kron, who has worked on the survey as a Fermilab and University of Chicago scientist for more than 10 years. “This latest measurement allowed us to exploit sound waves created about 400,000 years after the Big Bang. Our result has an impressive accuracy of two percent and supports the standard model of the accelerated expansion of the universe.”
- The measurement obtained fixes the scale of the universe when it was half its present age with an accuracy of 2%, the most accurate ever obtained for that time. The results were released yesterday.
- Researchers from the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), the Institut de Ciències de l’Espai (ICE-CSIC,IEEC), the Institut de Física d’Altes Energies (IFAE) and the Instituto de Física Teórica (UAM-CSIC) have led the scientific analysis of the data.
We now have a standard model of cosmology, the current version of the Big Bang theory. Although it has proved very successful, its consequences are staggering. We know only 5% of the content of the universe, which is normal matter. The remaining 95% is made up of two exotic entities that have never been produced in the laboratory and whose physical nature is still unknown. These are dark matter, which accounts for 25% of the content of the cosmos, and dark energy, which contributes 70%. In the standard model of cosmology, dark energy is the energy of empty space, and its density remains constant throughout the evolution of the universe.
The Cerro Tololo Interamerican Observatory (CTIO) in the Chilean Andes. Image credit: DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/ AURA
According to this theory, sound waves propagated in the very early universe. In those early stages, the universe had an enormous temperature and density. The pressure in this initial gas tried to push the particles that formed it apart, while gravity tried to pull them together, and the competition between the two forces created sound waves that propagated from the beginning of the universe until about 400,000 years after the Big Bang. At that time, the radiation and matter stopped interacting, and the waves were frozen, leaving an imprint on the spatial distribution of matter. This imprint is observed as a small preferential accumulation of galaxies separated by a characteristic distance, called the Baryon Acoustic Oscillations (BAO) scale by cosmologists, and corresponds to the distance traveled by the sound waves in those 400,000 years.
A new measurement of the cosmic distance
The Dark Energy Survey (DES) has just measured the BAO scale when the universe was half its present age with an accuracy of 2%, the most accurate determination yet at such an early epoch, and the first time an imaging-only measurement is competitive with large spectroscopy campaigns specifically designed to detect this signal.
Signal from Baryon Acoustic Oscillations (BAO) in the Dark Energy Survey (DES) data. When plotting the number of galaxy pairs as a function of their angular separation in the sky, we find an excess of pairs at 2.90 degrees. This is caused by BAO waves that have traveled hundreds of millions of light-years since the Big Bang. These waves subtend a size on the sky somewhat larger than predicted by the standard model of cosmology and the Planck data. Image credit: Dark Energy Survey Collaboration.
The distance the sound wave travels in the early universe depends on well-known physical processes, so it can be determined with great precision, setting a yardstick for the universe. It is what cosmologists call a standard ruler. In this case, it has a length of about 500 million light-years. By observing the angle that this standard ruler subtends in the sky at different distances (or, in other words, at different epochs in the universe), one can determine the history of the cosmic expansion and, with it, the physical properties of dark energy. In particular, it can be determined by analyzing the cosmic microwave background, the radiation released when atoms were formed, 400,000 years after the Big Bang that gives us a snapshot of the very early universe, as published by the Planck collaboration in 2018. It can also be determined in the late universe by studying the BAO scale in galaxy mappings as DES has done. Analyzing the consistency of both determinations is one of the most demanding tests of the standard model of cosmology.
“It is a source of pride to see how, after almost twenty years of continuous effort, DES produces scientific results of the highest relevance in cosmology,” says Eusebio Sánchez, head of the cosmology group at CIEMAT. “It is an excellent reward for the effort invested in the project.”
“What we observed is that galaxies have a greater tendency to be separated from each other by an angle of 2.90 degrees on the sky compared to other distances,” comments Santiago Ávila, a postdoctoral researcher at IFAE and one of the coordinators of the analysis. “That’s the signal! The wave can be seen clearly in the data,” he adds, referring to the first figure. “It’s a subtle preference, but statistically relevant,” he says, “and we can determine the wave pattern with an accuracy of 2%. For reference, the full moon occupies half a degree in diameter in the sky. So if we were able to see the galaxies with the naked eye, the BAO distance would look like 6 full moons.”
16 million galaxies to measure the universe 7 billion years ago
To measure the BAO scale, DES has used 16 million galaxies, distributed over one-eighth of the sky, that have been specially selected to determine how far away they are with sufficient precision.
“It is important to select a sample of galaxies that allows us to measure the BAO scale as accurately as possible,” says Juan Mena, who did his Ph.D. at CIEMAT on this study and is now a postdoctoral researcher at the Laboratory of Subatomic Physics and Cosmology in Grenoble (France). “Our sample is optimized to have a good compromise between a larger number of galaxies and the certainty with which we can determine their distance.”
In gold, we see the Dark Energy Survey BAO scale measurement, which deviates from the standard model (horizontal line at 1 in this plot) by 4%, while the uncertainties associated with the analysis are 2% (indicated by the golden vertical bar). This discrepancy could be a clue about dark energy or a mere statistical fluctuation, with a 5% chance. This measurement has been made by observing galaxies that emitted their light when the Universe, which is 14 billion years old, was about half its present age. In blue are shown measurements from the Baryonic Oscillations Spectroscopic Survey (BOSS) and its extension (eBOSS). DES gives us the most accurate measurement of when the Universe was about 7 billion years old. Image credit: Dark Energy Survey Collaboration.
Cosmological distances are so large that light takes billions of years to reach us, thus allowing us to observe the cosmic past. The sample of galaxies used in this study opens a window into the universe seven billion years ago, slightly less than half its present age.
“One of the most complicated tasks in the process is to clean the galaxy sample of observational contaminants: distinguishing between galaxies and stars or mitigating the effects of the atmosphere on the images,” says Martín Rodríguez Monroy, a postdoctoral researcher at the IFT in Madrid.
Clues about the mysterious dark energy
An interesting finding of this study is that the size these waves occupy on the sky is 4% larger than predicted from measurements made by ESA’s Planck satellite in the early universe using the cosmic microwave background radiation. Given the sample of galaxies and the uncertainties of the analysis, this discrepancy has a 5% chance of being a mere statistical fluctuation. If it were not, we could be looking at one of the first clues that the current theory of cosmology is not quite complete, and the physical nature of the dark components is even more exotic than previously thought. “For example, dark energy may not be the energy of the vacuum. Its density may change with the expansion of the universe, or even space may be slightly curved,” says Anna Porredon, a Spanish researcher at the Ruhr University Bochum (RUB) in Germany. This researcher, a fellow of the Marie Skłodowska-Curie Actions program of the European Union, has been one of the coordinators of this analysis.
The BAO scale has been measured by other cosmological projects before DES at different ages of the universe, mainly the Baryonic Oscillation Spectroscopic Survey (BOSS) and its extension (eBOSS), which were designed for this purpose (see second figure). However, the DES measurement is the most accurate at such an early age of the universe, with half the uncertainty of eBOSS at that time. The significant increase in precision has made it possible to reveal the possible discrepancy in the BAO scale with respect to the standard model of cosmology.
“To follow this lead, the next crucial step is to combine this information with other techniques explored by DES to understand the nature of dark energy”, comments Hugo Camacho, a postdoctoral researcher at Brookhaven National Laboratory (USA), formerly at the Institute of Theoretical Physics at São Paulo State University in Brazil (IFT-UNESP) and member of the Laboratorio Interinstitucional de e-Astronomia (LIneA), and adds “Moreover, DES also paves the way for a new era of discoveries in cosmology, which will be followed by future experiments with even more precise measurements.”
The Dark Energy Survey
As its name suggests, DES is a large cosmological project specially conceived to study the properties of dark energy. It is an international collaboration of more than 400 scientists from seven countries with its headquarters at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, near Chicago. The project is designed to use four mutually complementary methods: cosmological distances with supernovae, the number of galaxy clusters, the spatial distribution of galaxies, and the weak gravitational lensing effect (more details at https://www.darkenergysurvey.org/the-des-project/science/).
In addition, these methods can be combined to obtain higher statistical power and better control of the observations, which are expected to be consistent. The combination of the gravitational lensing effect with the spatial distribution of galaxies is especially relevant. These analyses test the cosmological model in a very demanding way. Results using half of the DES data have already been published to great acclaim, and the final measurements, using the full data set of more than 150 million galaxies, are expected to be published later this year. “DES allows us to understand for the first time whether the accelerating expansion of the Universe, which began 6 billion years ago, is consistent with our current model for the origin of the Universe,” comments Martin Crocce, who co-coordinates this latest analysis from ICE.
Focal plane of DECam (Dark Energy Camera). It contains 62 ultra-sensitive CCD sensors specially designed for the DES project, and allows imaging of the universe with unprecedented depth. Image credit: DOE/FNAL/DECam/R. Hahn/CTIO/NOIRLab/NSF/ AURA
To use all these techniques, the DES built the 570 Megapixel Dark Energy Camera (DECam), one of the largest and most sensitive cameras in the world. It is installed on the Víctor M. Blanco telescope, with a 4m diameter mirror, at the Cerro Tololo Inter-American Observatory in Chile, operated by the US NSF’s NOIRLab. DES has mapped one-eighth of the celestial vault to an unprecedented depth. It took 4-color images between 2013 and 2019 and is currently in the final phase of the scientific analysis of these images. Spanish institutions have been part of the project since its inception in 2005 and, in addition to having collaborated prominently in the design, manufacture, testing, and installation of DECam and data acquisition, have important responsibilities in DES scientific management to date.
More information is available at www.darkenergysurvey.org/collaboration.
DES contacts:
IFAE – Dr. Santiago Ávila, postdoctoral researcher, savila@ifae.es
CIEMAT – Dr. Eusebio Sánchez, research scientist, eusebio.sanchez@ciemat.es
IFT-UAM/CSIC – Dr. Martín Rodríguez-Monroy, postdoctoral researcher, martin.rodriguez@uam.es
ICE – Dr. Martín Crocce, tenured scientist, crocce@ice.csic.es
Reference: https://arxiv.org/abs/2402.10696
Fermi National Accelerator Laboratory is America’s premier national laboratory for particle physics research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s website at https://www.fnal.gov and follow us on Twitter @Fermilab.
The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Shishir Shetty grew up in India and studied aeronautical engineering. In 2013, he came to the United States for his Master’s degree. Originally working on projects related to aircraft structures in school, Shetty became interested in Fermilab due to his interest in building structures from scratch and the exceptional engineering environment at the lab
This year, Shetty is organizing activities for Engineers Week at Fermilab as the co-chair of the laboratory’s Engineering Advisory Council.
“The ecosystem we have is unique,” said Shetty, who joined Fermilab in 2017. He appreciates that Fermilab brings together people of all ages, nationalities and genders and provides guidance that empowers them to solve problems in ways they think would work best and be most efficient. “You get to make tangible impact in the whole life cycle of a project.”
At Fermilab, the level of detail of engineering needed to go into the tasks that engineers pursue is high. Describing it as “engineering refinement at its best,” Shetty explained how such high-precision engineering cannot have any wiggle room in the variables. The deliverables of a project are often subject to extreme requirements. “The conditions are extraordinary,” he said.
Fermilab engineer Shishir Shetty is co-chair of the laboratory’s Engineering Advisory Council. Photo: Dan Svoboda, Fermilab
A favorite design project that Shetty worked on was the transport system for a delicate neutrino detection system built for the Short-Baseline Near Detector at Fermilab. The move was very complex because the transport had many limiting conditions: There could be no significant vibration, no moisture seeping into the detection system. No dust and no light were allowed to enter. And the engineers had to account for the detector’s high center of gravity. The team designed a special transport frame and—very slowly—moved the detector on a trailer from the assembly facility to the research facility. “To put it together was an almost insurmountable task,” he said.
When Shetty was first applying to work at Fermilab, one thing that stood out to him was how at Fermilab the engineers were building many unique structures from scratch. This process involved conceiving the project, looking for the whole life cycle of a project from engineering analysis to fabrication and testing, and then delivering it. He also appreciates the culture at Fermilab: he thinks people working here have a mission in mind and are motivated for science; the problems they are solving are rigorous. “It’s extremely challenging. The challenges that you get, and the ways you solve them, and the aptitude of the people around you are mind boggling.”
Mayling Wong-Squires is Fermilab’s chief engineer and head of the Mechanical Support Department in the Accelerator Directorate. She has worked at Fermilab for over 25 years.
“Engineers at Fermilab work on a wide breadth and depth of technical work, such as maintaining the operations of particle accelerators and experiments, laying groundwork research in artificial intelligence, quantum and microelectronics, designing future accelerators and experiments, and maintaining the infrastructure of the lab,” said Wong-Squires. “For many projects, Fermilab engineers cannot just go out and buy equipment from the local hardware store.” Instead, they either ask vendors to push the limits of their technology or they outright design it themselves.
“That’s what makes working at Fermilab challenging and fun,” Wong-Squires said. “It requires engineers to return to textbooks from college. If they don’t find what they’re looking for, they innovate, and then they might end up writing the future textbook. It’s what we’re proud of here.”
Engineers Week
Engineers Week, founded by the National Society of Professional Engineers in 1951, is a weeklong event that takes place yearly every February. At Fermilab, the week serves as a time for engineers to convene and attend various activities and presentations.
Among the events offered for employees, users and contractors this year will be a plenary session with three divisions. One will bring together engineers from many disciplines to talk about the accomplishments of the past year; another will commemorate Helen Edwards, who was a lead figure in the design of the Tevatron at Fermilab; the third will feature keynote speaker Dr. Asmeret Asefaw Berhe, director of the Department of Energy’s Office of Science. Fermilab’s Integrated Engineering Research Center will feature posters and engineering exhibitions from both Fermilab and external groups.
Other events include a hackathon, which will provide creative, innovative time for engineers to work on a project of their own choosing. There will also be tours of underground and experimental areas at Fermilab intended for engineers who joined the laboratory in recent years.
“Engineering is all about observing things around us,” Shetty said. He went on to explain that, for him, engineering cannot be isolated to simply assignments done in the workplace. “It goes beyond,” Shetty said. “It is a part of your life, your observation of things, how they work, how they come together.”
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
India’s Department of Atomic Energy, or DAE, reached a milestone in their participation in building a 215-meter-long particle accelerator in the United States, known as the Proton Improvement Plan II project, or PIP-II. DAE recently informed the U.S. Department of Energy that India is officially moving from the research and development phase to the construction phase for its contributions to the PIP-II project at DOE’s Fermi National Accelerator Laboratory.
This significant transition solidifies a scientific partnership between the United States and India that has been nearly 20 years in the making. DAE institutions now can start to construct the components that they will send to the U.S. to enable the PIP-II project.
Chairman of Atomic Energy Commission of India Ajit Kumar Mohanty stated, “The sustained collaborative efforts during the research and development phase of PIP-II have validated and demonstrated many interesting and exciting developments that would be very important for building next generation accelerators for science and technological applications in India. The success of the research and development phase have facilitated the smooth transition to the construction phase of PIP-II. This success has also provided very high confidence in reaffirming our commitment of in-kind contribution of $140 million and extending all possible support till scheduled completion of PIP-II activities successfully.”
This rendering shows the buildings that will house the new PIP-II particle accelerator at Fermilab. Construction of the cryoplant building, shown at the top of this image, is complete. Fermilab’s 16-story Wilson Hall is partially visible in the bottom right corner. Illustration: Fermilab
In June, Prime Minister Narendra Modi of India and U.S. President Joe Biden met to deepen bilateral cooperation between the two countries on cutting-edge scientific infrastructures. The resulting White House statement (item no. 10) highlighted DAE’s in-kind contribution toward the collaborative development of the PIP-II accelerator.
“We are very excited about India’s critical technical contributions to the Proton Improvement Plan II project at the Fermi National Accelerator Laboratory. These contributions will help to deliver a record-setting proton beam that will power scientific discoveries for years to come,” said Asmeret Asefaw Berhe, DOE’s director of the Office of Science. “We look forward to continuing this longstanding partnership between India’s Department of Atomic Energy and the U.S. Department of Energy.”
The PIP-II project is building a state-of-the-art superconducting linear accelerator at Fermilab in Batavia, Illinois, 40 miles west of Chicago. It will enable the world’s most intense beam of neutrinos that scientists will shoot from Fermilab in Illinois to the gigantic particle detectors of the Deep Underground Neutrino Experiment in Lead, South Dakota. DUNE will be the most comprehensive neutrino experiment ever built, with the goal of uncovering secrets of the universe by studying the properties of the elusive neutrinos.
“We are thrilled that our partners in India have reached this major milestone in their PIP-II participation,” said Fermilab Director Lia Merminga. “Many people have worked hard for years to make sure this partnership could thrive. We at Fermilab value deeply the expertise and capabilities of our colleagues in India and I look forward to working with the DAE institutions to build the PIP-II particle accelerator.”
The PIP-II partnership is a symbiotic relationship and part of the Indian Institutions and Fermilab Collaboration. While providing next generation accelerator capabilities, the collaboration on PIP-II also provides Indian scientists and engineers the training, technical insight and know-how for the development of their domestic particle accelerator program and future projects.
PIP-II is the first particle accelerator on U.S. soil to be built with significant contributions from international partners. Institutions in France, India, Italy, Poland and the United Kingdom are contributing technologies, instrumentation and expertise to build the accelerator.
In India, participating institutions include the Bhabha Atomic Research Centre in Mumbai, the Inter-University Accelerator Centre in New Delhi, the Raja Ramanna Centre for Advanced Technology in Indore, and the Variable Energy Cyclotron Centre in Kolkata.
Many of these Indian institutions will provide a significant number of technical components for PIP-II, including superconducting acceleration structures, electromagnets and radio-frequency power sources. These will be fabricated in India and transported to Fermilab for installation.
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Chicago-based composer and accomplished pianist Mischa Zupko has been named 2024 guest composer by the Fermi Research Alliance. In collaboration with scientists at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, the Civitas Ensemble in Chicago and saxophonist Timothy McAllister, he will create music to interpret particle science in new ways.
“From what I have come to understand, the ability to imagine, in a physical sense, phenomena relating to the behavior and interaction of elementary particles is impossible, but the attempt to imagine, is where the beauty lies,” he said.
For many of his compositions, Zupko draws inspiration from themes of the universe, cosmic phenomena and mathematical models. Eclipse: Chamber Music of Mischa Zupko, with violinist Sang Mee Lee and cellist Wendy Warner, was recorded by Cedille Records in 2016 and conveys the alignment of the sun and moon, while the evening sky is the focal point in his cello piece From Twilight. Zupko stated in his guest composer proposal that these subjects are “spiritual” to him and to the music that he writes. He is eager to work with Fermilab scientists to musically explore projects such as the Deep Underground Neutrino Experiment.
Guest composer Mischa Zupko will work with Fermilab scientists to interpret particle science in new ways. Photo: Dan Svoboda, Fermilab
Zupko will not only collaborate with scientists on his Fermilab composition, but also with fellow chamber musicians Winston Choi, piano; Yuan-Qing Yu, violin; and Ken Olsen, cello, who are the members of the Civitas Ensemble, and guest Timothy McAllister, saxophone. While Zupko wrote Eclipse based on a specific mathematical model that he constructed, he hopes to compose his Fermilab piece based on a scientific model. He plans to include the completed composition as a world premiere recording on Cedille Records for a new release of his work in 2026.
“Though the mathematics [represented by Eclipse] are simple, they were essential in the process to achieve the very specific effect this piece intended and informed the intuitive aspects of the writing in profound ways,” he said. “I have always wanted to go deeper into this process, modeling numeric sequences on actual data from running experiments to see if the data itself can serve as a link between the various ways we experience our reality.”
Zupko is a third-generation composer. He received a Bachelor of Music in piano performance from Northwestern University, and a master’s degree and a doctorate in composition from Indiana University Bloomington. He has been named guest artist and participated in residency programs at various institutions, including the Fulcrum Point New Music Project, the Music Institute of Chicago, Western Michigan University, and Roosevelt University. Zupko has most recently had his music performed at Chamber Music Northwest, the International Tuba and Euphonium Conference, and the Grant Park Music Festival in Millennium Park, among others. Since 2010, he has served as lecturer of musicianship studies at DePaul University.
“Mischa Zupko’s profound grasp of musical theory and composition coupled with a longstanding curiosity about particle physics, along with previous compositions inspired by cosmic phenomena, renders him the ideal choice as the 2024 FRA guest composer at Fermilab,” said Visual Arts Coordinator Georgia Schwender, who manages the FRA guest composer program at Fermilab on behalf of FRA.
Editor’s note: Work created by former FRA guest composers and artists are featured in the public exhibition Beyond the Visible at the Schingoethe Center of Aurora University Jan. 29 – May 10, 2024. The exhibition will highlight Fermilab-inspired work by Mare Hirsch, David Ibbett, Jim Jenkins, Chris Klapper & Patrick Gallagher, Ricardo Mondragon, Ellen Sandor and Roger Zare.
The FRA guest composer program at Fermilab is funded by the Fermi Research Alliance, which manages Fermilab for the U.S. Department of Energy’s Office of Science. Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.