Research, teaching and outreach in Physics at UW–Madison
Magellanic Stream arcing over Milky Way may be five times closer than previously thought
Our galaxy is not alone. Swirling around the Milky Way are several smaller, dwarf galaxies — the biggest of which are the Small and Large Magellanic Clouds, visible in the night sky of the Southern Hemisphere.
During their dance around the Milky Way over billions of years, the Magellanic Clouds’ gravity has ripped from each of them an enormous arc of gas — the Magellanic Stream. The stream helps tell the history of how the Milky Way and its closest galaxies came to be and what their future looks like.
New astronomical models developed by scientists at the University of Wisconsin–Madison and the Space Telescope Science Institute recreate the birth of the Magellanic Stream over the last 3.5 billion years. Using the latest data on the structure of the gas, the researchers discovered that the stream may be five times closer to Earth than previously thought.
The findings suggest that the stream may collide with the Milky Way far sooner than expected, helping fuel new star formation in our galaxy.
“The Magellanic Stream origin has been a big mystery for the last 50 years. We proposed a new solution with our models,” says Scott Lucchini, a graduate student in physics in Elena D’Onghia’s group at UW–Madison and lead author of the paper. “The surprising part was that the models brought the stream much closer to the Milky Way.”
In 2012, scientists at CERN’s Large Hadron Collider announced they had observed the Higgs boson particle, verifying many of the theories of physics that rely on its existence.
Since then, scientists have continued to search for the properties of the Higgs boson and for related particles, including an extremely rare case where two Higgs boson particles appear at the same time, called di-Higgs production.
“We’ve had some searches for di-Higgs right now, but we don’t see anything significant yet,” said Alex Wang, a PhD student in experimental high energy physics at UW–Madison. “It could be because it doesn’t exist, which would be interesting. But it also could just be because, according to the Standard Model theory, it’s very rare.”
Wang will have a chance to aid in the search for di-Higgs production in more ways than one. Starting in November, he will spend a year at the SLAC National Accelerator Laboratory as an awardee in the Department of Energy Office of Science Graduate Student Research Program.
The program funds outstanding graduate students to pursue thesis research at Department of Energy (DOE) laboratories. Students work with a DOE scientist on projects addressing societal challenges at the national and international scale.
At the SLAC National Accelerator Laboratory, Wang will primarily work on hardware for a planned upgrade of the ATLAS detector, one of the many detectors that record properties of collisions produced by the Large Hadron Collider. Right now, ATLAS collects an already massive amount of data, including some events related to the Higgs boson particle. However, Higgs boson events are extremely rare.
In the future, the upgraded High-Luminosity Large Hadron Collider (HL-LHC) will enable ATLAS to collect even more data and help physicists to study particles like the Higgs boson in more detail. This will make it more feasible for researchers to look for extremely rare events such as di-Higgs production, Wang said. The ATLAS detector itself will also be upgraded to adjust for the new HL-LHC environment.
“I’m pretty excited to go there because SLAC is essentially where they’ll be assembling the innermost part of the ATLAS detector for the future upgrade,” Wang said. “So, I think it’s going to be a really central place in the future years, at least for this upgrade project.”
Increasing the amount of data a sensor collects can also cause problems, such as radiation damage to the sensors and more challenges sorting out meaningful data from background noise. Wang will help validate the performance of some of the sensors destined for the upgraded ATLAS detector.
“I’m also pretty excited because for the data analysis I’m doing right now, it’s mainly working in front of a computer, so it will be nice to have some experience working with my hands,” Wang said.
At SLAC, he will also spend time searching for evidence of di-Higgs production.
Wang’s thesis research at UW–Madison also revolves around the Higgs boson particle. He sifts through data from the Large Hadron Collider to tease out which events are “signals” related to the Higgs boson, versus events that are “backgrounds” irrelevant to his work.
One approach Wang uses is to predict how many signal events researchers expect to see, and then determine if the number of events recorded in the Large Hadron Collider is consistent with that prediction.
“If we get a number that’s consistent with our predictions, then that supports the existing model of physics that we have,” Wang said. “But for example, if you see that the theory predicts we’d have 10 events, but in reality, we see 100 events, then that could be an indication that there’s some new physics going on. So that would be a potential for discoveries.”
The Department of Energy formally approved the U.S. contribution to the High-Luminosity Large Hadron Collider accelerator upgrade project earlier this year. The HL-LHC is expected to start producing data in 2027 and continue through the 2030s. Depending on what the future holds, Wang may be able to use data from the upgraded ATLAS detector to find evidence of di-Higgs production. If that happens, he also will have helped build the machine that made it possible.
Magnetic fields implicated in the mysterious midlife crisis of stars
This post was originally published by the Royal Astronomical Society. UW–Madison physics graduate student Bindesh Tripathi is the lead author of the scientific publication.
Middle-aged stars can experience their own kind of midlife crisis, experiencing dramatic breaks in their activity and rotation rates at about the same age as our Sun, according to new research published today in Monthly Notices of the Royal Astronomical Society: Letters. The study provides a new theoretical underpinning for the unexplained breakdown of established techniques for measuring ages of stars past their middle age, and the transition of solar-like stars to a magnetically inactive future.
Astronomers have long known that stars experience a process known as ‘magnetic braking’: a steady stream of charged particles, known as the solar wind, escapes from the star over time, carrying away small amounts of the star’s angular momentum. This slow drain causes stars like our Sun to gradually slow down their rotation over billions of years.
In turn, the slower rotation leads to altered magnetic fields and less stellar activity – the numbers of sunspots, flares, outbursts, and similar phenomena in the atmospheres of stars, which are intrinsically linked to the strengths of their magnetic fields.
This decrease in activity and rotation rate over time is expected to be smooth and predictable because of the gradual loss of angular momentum. The idea gave birth to the tool known as ‘stellar gyrochronology’, which has been widely used over the past two decades to estimate the age of a star from its rotation period.
However recent observations indicate that this intimate relationship breaks down around middle age. The new work, carried out by Bindesh Tripathi at UW–Madison and the Indian Institute of Science Education and Research (IISER) Kolkata, India, provides a novel explanation for this mysterious ailment. Prof. Dibyendu Nandy, and Prof. Soumitro Banerjee of IISER are co-authors.
Using dynamo models of magnetic field generation in stars, the team show that at about the age of the Sun the magnetic field generation mechanism of stars suddenly becomes sub-critical or less efficient. This allows stars to exist in two distinct activity states – a low activity mode and an active mode. A middle aged star like the Sun can often switch to the low activity mode resulting in drastically reduced angular momentum losses by magnetized stellar winds.
Prof. Nandy comments: “This hypothesis of sub-critical magnetic dynamos of solar-like stars provides a self-consistent, unifying physical basis for a diversity of solar-stellar phenomena, such as why stars beyond their midlife do not spin down as fast as in their youth, the breakdown of stellar gyrochronology relations, and recent findings suggesting that the Sun may be transitioning to a magnetically inactive future.”
The new work provides key insights into the existence of low activity episodes in the recent history of the Sun known as grand minima – when hardly any sunspots are seen. The best known of these is perhaps the Maunder Minimum around 1645 to 1715, when very few sunspots were observed.
The team hope that it will also shed light on recent observations indicating that the Sun is comparatively inactive, with crucial implications for the potential long-term future of our own stellar neighbor.
Welcome, incoming MSPQC students!
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.
Flexible, easy-to-scale nanoribbons move graphene toward use in tech applications
From radio to television to the internet, telecommunications transmissions are simply information carried on light waves and converted to electrical signals.
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.”
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.
After record-breaking application numbers and the most unique recruiting season yet, the Department of Physics is pleased to introduce the 30 students of the incoming Ph.D. class of 2021!
“This year’s incoming Ph.D. class is a remarkably strong and diverse cohort who have overcome truly historic obstacles to join us,” says Ph.D. admissions committee chair, Prof. Shimon Kolkowitz. “I couldn’t be more excited to welcome them to our department and to witness the great work they will accomplish in their time here.”
602 students applied for one of 91 admissions spots, the most applications the department has received in at least the past decade (based on available graduate school data).
Some highlights of the incoming class include:
Students coming from 18 U.S. states and three other countries (China, India, and Malaysia)
22 expressing a preference for experiment, with the rest expressing a preference for theory only, or either/undecided
Three Advanced Opportunity Fellowship (AOF) eligible students
Two students who were named 2021 NSF Graduate Research Fellows
This year’s incoming class is also the first to ever participate in “Virtual Visit Days,” thanks to the COVID-19 pandemic. Though perhaps not as exciting as visiting campus in person, admitted students could still meet with faculty to discuss research opportunities, participate in discussions and virtual games nightswith current students, and watch videos — many newly-created just for these visits — about the University, the city of Madison, and research in our department.
“Thank you to all the prospective students for their engagement and enthusiasm throughout the admissions and virtual visit process,” says Michelle Holland, graduate program coordinator.“We are beyond thrilled to welcome the Class of 2021 to the Physics Ph.D. Program at UW–Madison as we find our ‘new normal’ in being together on campus this fall.”
The department would like to send a huge round of applause to everyone who participated in recruitment this year, especially current graduate students on the recruitment committee: Trevor Oxholm, Abigail Shearrow, Kunal Sanwalka, Susmita Mondal, Winnie Wang. We also thank graduate program coordinators Michelle Holland and Jackson Kennedy for organizing and running the virtual visit days, Dan Bradley for once again providing IT solutions to help the admissions process and visit days run smoothly, and Sarah Perdue for website development and video production.
The department also thanks the Ph.D. admissions committee for their thorough evaluation of the applicants. In addition to Kolkowitz, the committee members are Profs. Keith Bechtol, Stas Boldyrev, Victor Brar, Mark Eriksson, Ke Fang, and Jeff Parker.
One student accepted our admissions offer but has deferred to 2022.
This new award category recognizes graduate students in L&S who provided exceptional continuity of instruction support to their department or delivered exceptional student experience in a remote instructional setting during the COVID-19 pandemic.
Bonner was nominated for his work as a TA in Physics 109, Physics in the Arts, by one of the course’s instructors, Prof. Pupa Gilbert. Physics 109 is a quantitative-reasoning course offered to non-science majors, typically serving more than 200 students.
“The students are terrified of physics, and are not quantitative thinkers, thus it is especially important for Physics in the Arts TAs to be kind, friendly, and not intimidating,” Gilbert says. “Gage excels at all these challenges, and teaches masterfully. He is kind, intelligent, knowledgeable, and always in a good mood, making everyone feel comfortable and not intimidated.”
Gilbert nominated Bonner for the Continuation of Study award because of how effectively he adapted to the changes forced by the COVID-19 pandemic. For example, because in-person labs were no longer an option, Gilbert selected online labs, and asked the TAs to develop a series of interactive questions associated with each online experiment to help the students learn by doing. Bonner excelled at developing these questions. She also noted how well he interacts with students through the online Zoom lectures, helping to keep conversations going and being knowledgable, kind and effective with online instruction.
Based on course and TA evaluations, the students agree with Gilbert. Said one student in an evaluation:
“Gage has been a really awesome TA. He makes labs run so smoothly, responds to questions quickly and effectively, and reminds us [of] vital information. He was also super helpful in lectures. Letting the teachers know if there was a technical issue or question. He also made a really friendly and comfortable learning environment even with the restraints of BBC collaborate ultra.”
UW–Madison employs over 2,100 teaching assistants (TAs) across a wide range of disciplines. Their contributions to the classroom, lab, and field are essential to the university’s educational mission. To recognize the excellence of TAs across campus, the Graduate School supports the College of Letters & Science (L&S) in administering these awards.
Bonner has been a graduate student and TA in the department since Fall 2016.
Jimena González named Three Minute Thesis® finalist
Congrats to Jimena González, a physics graduate student in Keith Bechtol’s group, who is one of nine finalists for UW–Madison’s Three Minute Thesis® competition! Watch Jimena’s video on YouTube, and check out all nine finalists’ videos at the UW–Madison 3MT® website. The videos are only available through November 29. The finals will be held on February 3, 2021.
How do astronomers test-drive a telescope?
Graduate student Leslie Taylor helped fine-tune a high-energy gamma-ray telescope this summer. Detecting the Crab Nebula was the “gold standard” for success.