Dark Energy Survey releases most precise look at the universe’s evolution

a black background with lots of small bright white stars

This news piece has been slightly modified from this news story, first published by Fermilab. 

The Dark Energy Survey collaboration has created the largest ever maps of the distribution and shapes of galaxies, tracing both ordinary and dark matter in the universe out to a distance of more than 7 billion light years. The analysis, which includes the first three years of data from the survey, is consistent with predictions from the current best model of the universe, the standard cosmological model. Nevertheless, there remain hints from DES and other experiments that matter in the current universe is a few percent less clumpy than predicted.

New results from the Dark Energy Survey — a large international team that includes researchers from the University of Wisconsin–Madison — use the largest ever sample of galaxies over an enormous piece of the sky to produce the most precise measurements of the universe’s composition and growth to date. Scientists measured that the way matter is distributed throughout the universe is consistent with predictions in the standard cosmological model, the best current model of the universe.

Over the course of six years, DES surveyed 5,000 square degrees — almost one-eighth of the entire sky — in 758 nights of observation, cataloguing hundreds of millions of objects. The results, announced May 27, draw on data from the first three years — 226 million galaxies observed over 345 nights — to create the largest and most precise maps yet of the distribution of galaxies in the universe at relatively recent epochs.

Since DES studied nearby galaxies as well as those billions of light-years away, its maps provide both a snapshot of the current large-scale structure of the universe and a movie of how that structure has evolved over the course of the past 7 billion years.

profile photo of keith bechtol
Keith Bechtol

“This a stringent test of the current standard cosmological paradigm, a model proposing that 95% of the universe is dark matter and dark energy that we do not yet understand,” explains UW–Madison physics professor Keith Bechtol. “By measuring the apparent positions and shapes of hundreds of millions of galaxies in our survey, we test whether the cosmic structures that have formed in the universe today match the predictions based on structures observed in the early universe.”

To test cosmologists’ current model of the universe, DES scientists compared their results with measurements from the European Space Agency’s orbiting Planck observatory. Planck used light signals known as the cosmic microwave background to peer back to the early universe, just 400,000 years after the Big Bang. The Planck data give a precise view of the universe 13 billion years ago, and the standard cosmological model predicts how the dark matter should evolve to the present. If DES’s observations don’t match this prediction, there is possibly an undiscovered aspect to the universe. While there have been persistent hints from DES and several previous galaxy surveys that the current universe is a few percent less clumpy than predicted—an intriguing find worthy of further investigation—the recently released results are consistent with the prediction.

“In the area of constraining what we know about the distribution and structure of matter on large scales as driven by dark matter and dark energy, DES has obtained limits that rival and complement those from the cosmic microwave background,” said Brian Yanny, a Fermilab scientist who coordinated DES data processing and management. “It’s exciting to have precise measurements of what’s out there and a better understanding of how the universe has changed from its infancy through to today.”

a black background with lots of small bright white stars
Ten areas in the sky were selected as “deep fields” that the Dark Energy Camera imaged multiple times during the survey, providing a glimpse of distant galaxies and helping determine their 3-D distribution in the cosmos. Photo: Dark Energy

Ordinary matter makes up only about 5% of the universe. Dark energy, which cosmologists hypothesize drives the accelerating expansion of the universe by counteracting the force of gravity, accounts for about 70%. The last 25% is dark matter, whose gravitational influence binds galaxies together. Both dark matter and dark energy remain invisible and mysterious, but DES seeks to illuminate their natures by studying how the competition between them shapes the large-scale structure of the universe over cosmic time.

DES photographed the night sky using the 570-megapixel Dark Energy Camera on the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile, a Program of the National Science Foundation’s NOIRLab. One of the most powerful digital cameras in the world, the Dark Energy Camera was designed specifically for DES and built and tested at Fermilab. The DES data were processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

“These analyses are truly state-of-the-art, requiring artificial intelligence and high-performance computing super-charged by the smartest young scientists around,” said Scott Dodelson, a physicist at Carnegie Mellon University who co-leads the DES Science Committee with Elisabeth Krause of the University of Arizona. “What an honor to be part of this team.”

To quantify the distribution of dark matter and the effect of dark energy, DES relied on two main phenomena. First, on large scales, galaxies are not distributed randomly throughout space but rather form a weblike structure due to the gravity of dark matter. DES measured how this cosmic web has evolved over the history of the universe. The galaxy clustering that forms the cosmic web, in turn, revealed regions with a higher density of dark matter.

images shows a huge camera inside an observatory
The Dark Energy Survey photographed the night sky using the 570-megapixel Dark Energy Camera on the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile, a Program of the National Science Foundation’s NOIRLab. Photo: Reidar Hahn, Fermilab

Second, DES detected the signature of dark matter through weak gravitational lensing. As light from a distant galaxy travels through space, the gravity of both ordinary and dark matter can bend it, resulting in a distorted image of the galaxy as seen from Earth. By studying how the apparent shapes of distant galaxies are aligned with each other and with the positions of nearby galaxies along the line of sight, DES scientists inferred the spatial distribution (or clumpiness) of the dark matter in the universe.

Analyzing the massive amounts of data collected by DES was a formidable undertaking. The team began by analyzing just the first year of data, which was released in 2017. That process prepared the researchers to use more sophisticated techniques for analyzing the larger data set, which includes the largest sample of galaxies ever used to study weak gravitational lensing.

For example, calculating the redshift of a galaxy — the change in light’s wavelength due to the expansion of the universe — is a key step toward measuring how both galaxy clustering and weak gravitational lensing change over cosmic history.  The redshift of a galaxy is related to its distance, which allows the clustering to be characterized in both space and time.

“Redshift calibration is one topic where we significantly improved upon our year-1 data analysis,” said Ross Cawthon, a UW-Madison physics postdoc who led the redshift calibration efforts for two of the main galaxy samples. “We developed new methods and refined old ones. It has been a huge effort by DES members from all over the world.”

Ten regions of the sky were chosen as “deep fields” that the Dark Energy Camera imaged repeatedly throughout the survey. Stacking those images together allowed the scientists to glimpse more distant galaxies. The team then used the redshift information from the deep fields to calibrate measurements of redshift in the rest of the survey region. This and other advancements in measurements and modeling, coupled with a threefold increase in data compared to the first year, enabled the team to pin down the density and clumpiness of the universe with unprecedented precision.

Along with the analysis of the weak-lensing signals, DES also precisely measures other probes that constrain the cosmological model in independent ways: galaxy clustering on larger scales (baryon acoustic oscillations), the frequency of massive clusters of galaxies, and high-precision measurements of the brightnesses and redshifts of Type Ia supernovae. These additional measurements will be combined with the current weak-lensing analysis to yield even more stringent constraints on the standard model.

“DES has delivered cost-effective, leading-edge science results directly related to Fermilab’s mission of pursuing the fundamental nature of matter, energy, space and time,” said Fermilab Director Nigel Lockyer. “A dedicated team of scientists, engineers and technicians from institutions around the world brought DES to fruition.”

The DES collaboration consists of over 400 scientists from 25 institutions in seven countries.

“The collaboration is remarkably young. It’s tilted strongly in the direction of postdocs and graduate students who are doing a huge amount of this work,” said DES Director and spokesperson Rich Kron, who is a Fermilab and University of Chicago scientist. “That’s really gratifying. A new generation of cosmologists are being trained using the Dark Energy Survey.”

UW–Madison physics graduate student Megan Tabbutt was one of the many significant contributors to this work, developing new methods that contributed to an independent validation of the galaxy clustering analysis.

DES concluded observations of the night sky in 2019. With the experience of analyzing the first half of the data, the team is now prepared to handle the complete data set. The final DES analysis is expected to paint an even more precise picture of the dark matter and dark energy in the universe. And the methods developed by the team have paved the way for future sky surveys to probe the mysteries of the cosmos.

“This work represents a ‘big statement’ from the Dark Energy Survey. DES data combined with other observations provide world-leading constraints on the nature of dark energy,” Bechtol says. “At the same time, we are training a new generation of cosmologists, and pioneering advanced methodologies that will be essential to realize the full potential of upcoming galaxy surveys, including the Vera C. Rubin Observatory Legacy Survey of Space and Time.”

The recent DES results were presented in a scientific seminar on May 27. Twenty-nine papers are available on the arXiv online repository.

Dark Energy Survey result video Exploring 7 billion light years of space with the Dark Energy Survey

The Dark Energy Survey is a collaboration of more than 400 scientists from 25 institutions in seven countries. For more information about the survey, please visit the experiment’s website.

Yang Bai promoted to full professor

Profile photo of Yang Bai
Profile photo of Yang Bai
Yang Bai

The Department of Physics is pleased to announce that Prof. Yang Bai has been promoted to the rank of full professor.

“It is my pleasure and honor as Dean to approve Prof. Yang Bai’s promotion to Full Professor. His creativity and impressive breadth in particle physics research make him a leader not only on dark matter, but also more generally on Beyond-the-Standard-Model Physics,” says Eric Wilcots, Dean of the College of Letters & Science. “He is also a valued teacher, appreciated by students especially at the graduate level. Graduate students and junior researchers in Madison are in good hands.”

Bai joined the department in 2012, and was promoted to associate professor in 2017. In addition to his robust and well-funded research program, he has trained several successful graduate students, taught all levels of departmental courses, and served on several departmental and university committees.

“Professor Yang Bai is widely recognized as one of the leading theoretical particle physicists of his generation with a broad and vigorous research program, covering both the collider-related frontiers and the cosmic frontier. His work includes significant contributions in essentially every area related to dark matter,” says Sridhara Dasu, professor and department chair. “The Physics Department very strongly endorses the promotion of Yang Bai to Full Professor.”

Congrats, Prof. Bai on this well-earned recognition!

 

Several physics majors awarded Hilldale Fellowships

Six UW–Madison undergraduate physics or AMEP majors have been named 2021 Hilldale Fellows, in addition to one computer science major who is conducting their research in the Physics Department.

The Hilldale Undergraduate/Faculty Research Fellowship provides research training and support to undergraduates at UW–Madison. Students have the opportunity to undertake their own research project in collaboration with UW–Madison faculty or research/instructional academic staff. Approximately 97 – 100 Hilldale awards are available each year.

Three students are conducting research in the Department of Physics, including:

  • Mathematics and Physics major Gage Siebert, in Prof. Peter Timbie’s group
  • Physics major Haley Stueber, in Prof. Dan McCammon’s group
  • Computer Sciences major Nikhilesh Venkatasubramanian, in Prof. Tulika Bose’s group

The physics or AMEP majors who have been named Hilldale Fellows and are conducting research outside the department are:

  • Mathematics and Physics major Sam Christianson, with Saverio Spagnolie (Mathematics)
  • Astronomy – Physics, Biochemistry, Chemistry, Mathematics, Molecular & Cell Biology, Neurobiology, Physics, Psychology, and Zoology major Renxi Li, with Catherine Gallagher (Neurology)
  • AMEP major Shenwei Yin, with Joseph Andrews (Mechanical Engineering)
  • Computer Sciences and Physics major Heqiao (Wonder) Zhu, with Kevin Eliceiri (LOCI)

Welcome, incoming MSPQC students! 

Bucky Badger in a lab coat holding a prism with a rainbow coming out, and Welcome to Physics! above

The UW–Madison Physics Department is pleased to welcome 18 students to the M.S. in Physics – Quantum Computing program. These students make up the third cohort to begin the program and are the largest entering class to date.  

“We are really pleased and proud that the MSPQC program continues to grow and prosper in its third year,” says Bob Joynt, MSPQC Program Director and professor of physics. “We look forward to providing a great experience for the class of 2021. A particular focus this year will be the formation of collaborative teams that will push forward research in quantum computing.” 

 Of note, three women are in the entering class, marking the first time that women have enrolled in MSPQC. Other facts and figures about this year’s cohort include: 

  • 11 students are coming directly from completing their Bachelors 
  • Three students have Master’s degrees 
  • Six students have at least four years of professional experience, and four of those students have over 10 years professional experience 
  • 15 are international students, and seven of those students have attended U.S. institutions for previous studies 
  • The students’ academic backgrounds include physics, astronomy, engineering, and business administration.  

The department is following University guidelines and is planning for students to join us in Madison this fall, with in-person instruction. Over the summer, students can attend optional virtual orientation sessions to prepare for the program.  

“The pandemic imposed restrictions on our admissions and recruitment activities which forced us to work virtually, but I believe these barriers made our programming more accessible and led to the most diverse and determined incoming cohort of MSPQC students to date,” says Jackson Kennedy, MSPQC coordinator. “Although I have been able to meet our incredibly talented students virtually, I cannot wait to greet them in-person this Fall as we celebrate a long-awaited return to campus.” 

In addition to Joynt, the department thanks the other faculty who serve on the MSPQC admissions committee — Alex Levchenko, Robert McDermott, Maxim Vavilov and Deniz Yavuz — for application review. We also thank Michelle Holland and Jackson Kennedy for organizing recruiting efforts.  

 The MSPQC program welcomed its first students in Fall 2019 – the first-ever class of students in the U.S. to enroll in a quantum computing M.S. degree program. The accelerated program was born out of a recognized need to rapidly train students for the quantum computing workforce and is designed to be completed in 12 months. It provides students with a thorough grounding in the new discipline of quantum information and quantum computing.  

names of students, UG institute and degree: Brooke Becker UW–Madison Computer Engineering Soyeon Choi Vanderbilt University Physics, Computer Science Manish Chowdhary Indian Institute of Technology Dhanbad Computer Application Hua Feng Dalian University of Technology Atomic and Molecular Physics Jacob Frederick University of Washington Computer Engineering Amol Gupta Delhi Technological University Computer Engineering Yucheng He Zhengzhou University Automation Xunyao Luo Lafayette College Physics and Neuroscience Arjun Puppala Indian Institute of Technology Roorkee Power Systems Engineering Evan Ritchie University of St Thomas - Minnesota Physics & Math Mubinjon Satymov New York City College of Technology - CUNY Applied Computational Physics Yen-An Shih National Cheng Kung University Computer Science Qianxu Wang University of Michigan Physics Jiaxi Xu UC-Berkeley Physics Anirudh Yadav Indian Institute of Technology Dhanbad Computer Science Yukun Yang Nanjing University Astronomy Jin Zhang UW–Madison Physics & Philosophy Lin Zhao UW–Madison Computer Science and Physics
The incoming 2021 class of MSPQC students

San Lan Wu earns Phi Beta Kappa Excellence in Teaching Award

profile photo of Sau Lan Wu

On April 17, the Alpha Chapter of Wisconsin Phi Beta Kappa presented the 2021 Phi Beta Kappa Excellence in Teaching Award to Enrico Fermi distinguished Professor of Physics Sau Lan Wu. She was nominated by senior Yan Qian.

To view Qian’s nomination and Wu’s acceptance speeches at the 2021 Induction Ceremony, please visit https://pbk.wisc.edu/ceremony/.

Phi Beta Kappa is the nation’s oldest academic society honoring the liberal arts and sciences. Founded in 1776 at the College of William and Mary, ΦΒΚ stands for freedom of inquiry and expression, disciplinary rigor, breadth of intellectual perspective, the cultivation of skills of deliberation and ethical reflection, the pursuit of wisdom, and the application of the fruits of scholarship and research in practical life.

Celebrating IceCube’s first decade of discovery

graphic of the number 10 with a cartoon of the IceCube detectors in the 0. Background is of outerspace/night sky, lots of stars

It was the beginning of a grand experiment unlike anything the world had ever seen. Ten years ago today, the IceCube Neutrino Observatory fully opened its eyes for the first time.

Over the course of the previous seven years, dozens of intrepid technicians, engineers, and scientists had traveled to the South Pole—one of the coldest, driest, and most isolated places on Earth—to build the biggest, strangest telescope in the world. Crews drilled 86 holes nearly two-and-a-half kilometers deep and lowered a cable strung with 60 basketball-sized light detectors into each hole. The result was a hexagonal grid of sensors embedded in a cubic kilometer of ice about a mile below the surface of the Antarctic ice sheet. On December 18, 2010, the 5,160th light sensor was deployed in the ice, completing the construction of the IceCube Neutrino Observatory.

The purpose of the unconventional telescope was to detect signals from passing astrophysical neutrinos: mysterious, tiny, extremely lightweight particles created by some of the most energetic and distant phenomena in the cosmos. IceCube’s founders believed that studying these astrophysical neutrinos would reveal hidden parts of the universe. Over the course of the next decade, they would be proven right.

IceCube began full operations on May 13, 2011 — ten years ago today — when the detector took its first set of data as a completed instrument. Since then, IceCube has been watching the cosmos and collecting data continuously for a decade.

During its first few years of operation, IceCube accumulated vast amounts of data, but it wasn’t until 2013 that the observatory yielded its first major results.

For the full story, please visit https://icecube.wisc.edu/news/collaboration/2021/05/celebrating-icecubes-first-decade-of-discovery/

Flexible, easy-to-scale nanoribbons move graphene toward use in tech applications

greyscale scanning electron micrograph of graphene nanoribbons that looks like an intricate fingerprint. has also been described as a "zen garden"

From radio to television to the internet, telecommunications transmissions are simply information carried on light waves and converted to electrical signals.

Joel Siegel

Silicon-based fiber optics are currently the best structures for high-speed, long distance transmissions, but graphene — an all-carbon, ultra-thin and adaptable material — could improve performance even more.

In a study published April 16 in ACS Photonics, University of Wisconsin–Madison researchers fabricated graphene into the smallest ribbon structures to date using a method that makes scaling-up simple. In tests with these tiny ribbons, the scientists discovered they were closing in on the properties they needed to move graphene toward usefulness in telecommunications equipment.

“Previous research suggested that to be viable for telecommunication technologies, graphene would need to be structured prohibitively small over large areas, (which is) a fabrication nightmare,” says Joel Siegel, a UW–Madison graduate student in physics professor Victor Brar’s group and co-lead author of the study. “In our study, we created a scalable fabrication technique to make the smallest graphene ribbon structures yet and found that with modest further reductions in ribbon width, we can start getting to telecommunications range.”

For the full story, please visit: https://news.wisc.edu/flexible-easy-to-scale-nanoribbons-move-graphene-toward-use-in-tech-applications/

Searching for Sources of Gravitational Waves

a colorful graph showing degrees of sky on a graph's axes and plots of data indicating where gravitational waves may have come from

The entire astrophysical world was blown away by the first-ever binary neutron star collision seen in August 2017 (called ‘GW170817’). This event, identified as a kilonova, was the first to be seen in both gravitational waves, by the LIGO and Virgo detectors, as well as the electromagnetic spectrum, from gamma rays to radio waves (and covered previously in this Oct 2017 DArchive ). Since then, there have been dozens of new gravitational wave events.

A group of researchers in DES, the DESGW team, have focused on finding more electromagnetic counterparts to these gravitational wave events. Members of the Dark Energy Survey — including University of Wisconsin–Madison physics grad student Rob Morgan and postdoc Ross Cawthon, both in Prof. Keith Bechtol’s group —  look at two of the most intriguing events we have followed up with DECam since 2017.

For the full story, please visit The Dark Energy Survey post.