Photosynthesis plays a crucial role in shaping and sustaining life on Earth, yet many aspects of the process remain a mystery. One such mystery is how Photosystem II, a protein complex in plants, algae and cyanobacteria, harvests energy from sunlight and uses it to split water, producing the oxygen we breathe. Now researchers from the Department of Energy’s Lawrence Berkeley National Laboratory and SLAC National Accelerator Laboratory, together with collaborators from the University of Wisconsin–Madison and other institutions have succeeded in cracking a key secret of Photosystem II.
Uwe Bergmann
Using SLAC’s Linac Coherent Light Source (LCLS) and the SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, they captured for the first time in atomic detail what happens in the final moments leading up to the release of breathable oxygen. The data reveal an intermediate reaction step that had not been observed before.
The results, published today in Nature, shed light on how nature has optimized photosynthesis and are helping scientists develop artificial photosynthetic systems that mimic photosynthesis to harvest natural sunlight to convert carbon dioxide into hydrogen and carbon-based fuels.
“The splitting of water to molecular oxygen by photosynthesis has dramatically reshaped our early planet, eventually leading to complex life forms that rely on oxygen for respiration, including ourselves,” says Uwe Bergmann, a physics professor at UW–Madison. “Capturing the final steps of this process in real time with x-ray laser pulses, and bringing to light the individual atoms involved, is thrilling and adds an important piece to solving this over 3-billion-year-old puzzle.”
Big discoveries, lofty goals highlight astronomy Investiture panel
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This story was originally published by University Communications as part of their coverage of Chancellor Mnookin’s Investiture
A group of astronomers and physicists, including Physics professor Francis Halzen, shared the stories behind their groundbreaking discoveries and lofty goals before a packed house gathered at University of Wisconsin–Madison’s Marquee Theater on Thursday to celebrate the Investiture of Chancellor Jennifer Mnookin.
The scientists included UW–Madison professors Francis Halzen and Susanna Widicus Weaver, as well as Andrea Ghez, a professor at the University of California, Los Angeles and good friend of Chancellor Mnookin. The symposium was titled “Discovery Past, Present, and Future: Black Holes, Neutrinos, and Life in our Galaxy.”
The friendship between Mnookin and Ghez goes back more than 15 years and is filled with fond memories, among them a champagne toast they shared in Ghez’s backyard to mark her winning the 2020 Nobel Prize in Physics. An attorney with a skill for interpreting legalese, Mnookin ensured the celebratory moment would conform with California’s emergency public health rules during the first winter of the COVID-19 pandemic.
“One of the things I love about Chancellor Mnookin is she is a problem solver,” said Ghez, who shared the 2020 prize for the discovery of a supermassive black hole at the center of the Milky Way galaxy.
Ghez recounted the scientific principles, theories and observations that led to the discovery in a talk that reveled in the surprise of the scientific process — a process that is increasingly enabled by new technologies.
“What’s so fun about what I call ‘technology-enabled discovery’ is that almost everything we’ve been able to look at in the center of the galaxy and its environment is inconsistent with the predictions,” Ghez said. “I like to call that either job security or being a kid in a candy shop.”
The rise of new technologies to help answer fundamental questions about the universe was a common theme among the three panelists, who were introduced by Dean Eric Wilcots of the College of Letters & Science and an astronomer himself.
Halzen described the massive telescope built deep within the ice at UW’s IceCube Neutrino Observatory at the South Pole that has enabled the detection of neutrinos, along with plans for an ice-encased observatory 10 times its size. The ghostly particles zip across the universe unimpeded from high-energy sources like the supermassive black holes now believed to be at the center of virtually all large galaxies.
And Widicus Weaver recounted her work hunting for the chemical signatures that might help identify habitable exoplanets — research that has received a massive boost from the James Webb Space Telescope, which began its science mission less than a year ago.
The discussion began with a history lesson provided by Wilcots, who shared the story of Karl Jansky.
A 1927 graduate of UW–Madison who was known at the time as “the fastest skater on the Wisconsin hockey team,” Jansky went on to work for Bell Laboratories. There he sought to understand the sources of static and radio interference — work that eventually led Jansky to observe a major source of radio interference emanating from the constellation of Sagittarius. Decades later, Ghez discovered the likely source — the supermassive black hole at the center of the galaxy.
Jansky’s observations “effectively started the field of radio astronomy,” Wilcots said, noting UW–Madison’s prominent and ongoing contributions to the field via scientists like Halzen, Widicus Weaver and their many colleagues.
The contributions are in their own ways manifestations of the Wisconsin Idea, Mnookin said in her opening remarks.
“When we talk about the Wisconsin Idea and our impact beyond the borders of our campus, it is awesome to think that there are people in our midst pushing that line beyond our planet, our solar system and even our galaxy,” she said.
IceCube search for sub-TeV neutrino emission associated with LIGO/Virgo gravitational waves
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Gravitational waves (GWs) are produced by some of the most extreme astrophysical phenomena, such as black hole and neutron star mergers. They have long been suspected as astrophysical sources of neutrinos, ghostlike cosmic messengers hurtling through space unimpeded. Thus far, common astrophysical sources of neutrinos and photons, as well as common sources of gravitational waves and light, have been identified. However, no one has yet detected sources that emit both gravitational waves and neutrinos.
In a study recently submitted to The Astrophysical Journal, the IceCube Collaboration performed a new search for neutrinos from GWs at the GeV-TeV scale. Although no evidence of neutrino emission was found, new upper limits on the number of neutrinos associated with each gravitational wave source and on the total energy emitted by neutrinos for each source were set.
Previously, IceCube searched for neutrinos from GW sources using the TeV-PeV neutrinos detected by the main IceCube Neutrino Observatory, a cubic-kilometer detector enveloped in Antarctic ice at the South Pole. This time, collaborators used data taken with the DeepCore array, the innermost component of IceCube consisting of sensors more densely spaced than in the main array. DeepCore can detect lower energy (GeV and upward) neutrinos than is possible with the larger main array.
Example map of the sky in neutrinos, overlaid on the localization of gravitational wave event GW 151226. The source of the gravitational wave signal is indicated by the color scale, with darker colors indicating more probable location of the source. The eight neutrinos detected by IceCube DeepCore within ±500 seconds of the gravitational wave are indicated with crosses (best fit) and curves (90% containment). Several neutrinos are spatially compatible with the direction of GW151226, but the association is not statistically significant. The IceCube Upgrade will enable improved localization of such GeV-TeV neutrinos, possibly leading to detection of a common source of gravitational waves and neutrinos. Credit: IceCube Collaboration
The analysis looked for temporal and spatial correlations between 90 GW events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo gravitational wave detectors and neutrinos detected by DeepCore. The researchers found no significant excess of neutrinos from the direction of the GW events but set stringent upper limits on the neutrino flux and limits on the energies associated with neutrinos from each GW source.
“These results do not mean that all hope is lost for detecting such joint emissions,” says Aswathi Balagopal V., a postdoctoral associate at UW–Madison and co-lead of the analysis. “With improvements in directional reconstructions for low-energy neutrinos, which is expected with better methods and with the inclusion of the IceCube Upgrade, we will be able to achieve better sensitivities for such joint searches, potentially leading to a positive discovery.”
Dan McCammon earns L&S Distinguished Academic Advising Achievement Award
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The College of Letters & Science announced this week that Prof. Dan McCammon has been awarded a 2022-23 Distinguished Academic Advising Achievement Award, the highest advising honor the College bestows.
Persons honored with an L&S Academic Advisingaward are exceptional advisors. Recipients have demonstrated exemplary performance both in terms of their positive impact on students and through distinctive contributions to their department, unit, and/or the College of Letters & Science.
Dan McCammon
“Dan is widely known in the physics department for the care and concern he shows to all our students,” says Prof. Thad Walker, chair of the department’s Faculty Recognition committee. “Literally thousands of students have benefitted from his thoughtful, knowledgeable, and non-judgmental advice.”
McCammon joined the Physics faculty in 1980 and has served in a formal or informal advising role ever since. He works tirelessly on behalf of all students in a role which most of them are likely unaware of — as their representative and defender within the physics department.
Katiya Fosdick was one of those students. She was an astronomy-physics major who had been assigned an academic advisor in the astronomy department, but frequently turned to McCammon for discussions about the major, course selection, and issues with workload in courses.
“Dan fights and advocates to do right by his undergraduate constituents,” Fosdick says. “He is motivated by a sense of responsibility and service to students and acts on it.”
McCammon has served as a research advisor for over 220 undergraduate students, both physics and non-physics majors, in addition to his academic advising role. He has served as the faculty mentor to the Undergraduate Physics Club for three decades, worked with the L&S Honors program to increase the honors section offerings in physics courses, and worked closely with the undergraduate course committees to ensure that physics course requirements are appropriate for all students regardless of their graduate school plans.
“Dan has served as an exceptional advisor to thousands of students over decades of service, and his unique understanding and compassionate mentoring has positively impacted students’ lives in myriad ways,” Walker says. “It is a pleasure that the College is acknowledging his outstanding work over so many years with this Distinguished Achievement Advising Award.”
Justin Vandenbroucke receives Vilas Associates award
UW–Madison physics professor Justin Vandenbroucke was selected as one of 23 awardees of the Vilas Associates Competition. The announcement was made recently by the Office of the Vice Chancellor for Research and Graduate Education.
The competition recognizes “new and ongoing research of the highest quality and significance,” and is open to tenure-track assistant professors and tenured faculty within 20 years of their tenure date. Recipients are chosen based on their research proposals, with winners receiving up to two-ninths of research salary support for the summers of 2023 and 2024, in addition to a $12,500 flexible research fund each of the fiscal years.
“This award will enable my group and me to build on our recent work by branching out in new directions,” says Vandenbroucke. “I’m grateful for the support we receive from the university, the physics department, and WIPAC.”
Vandenbroucke’s work at WIPAC includes research in neutrino astronomy, gamma-ray astronomy, and cosmic rays. Vandenbroucke leads the Distributed Electronic Cosmic-Ray Observatory (DECO), a citizen science project that allows users around the world to detect cosmic rays and other energetic particles with their cell phones and tablets. Vandenbroucke is a member of the IceCube Collaboration and the Cherenkov Telescope Array consortium and an affiliate member of the Fermi LAT collaboration.
The award will be used to support research in multimessenger astrophysics using IceCube and the IceCube Upgrade, now underway, in combination with gravitational wave and gamma-ray observations to discover and study cosmic particle accelerators.
The award is funded by the William F. Vilas Trust Estate.
Alex Levchenko earns L&S Distinguished Honors Faculty Award
Each year, the L&S Honors Program solicits student nominations of faculty members or instructional academic staff who have had a special impact as instructors of Honors courses, as supervisors of Honors theses, or as teachers and mentors of Honors students. The Faculty Honors Committee reviews these nominations and votes to confer Distinguished Honors Faculty status on the strongest nominees for these awards each spring.
Excerpt from student nomination:
As a classroom teacher, Prof. Levchenko is exceptional at explaining difficult concepts. He is really good at challenging students with homework problems, which are very involved and demanding but [helps them] understand materials and develop invaluable skills as a physicist. […] On top of being extremely competent in his research, he cares deeply about his students on a personal level, making sure students are doing ok in general in life and opening many doors for professional activities. As an aspiring theoretical physicist, Prof. Levchenko is someone I would not only like to work with but also want to be like when I reach that stage.
Awardees will be recognized at an L&S Honors Kick-off event this fall.
Physics students earn 2023 NSF graduate fellowships
The Graduate Research Fellowship Program (GRFP) supports high-potential scientists and engineers in the early stages of their careers. Each year, more than 12,000 applicants compete for ~2,000 fellowship awards. NSF GRFP awards are highly sought and competitive. The fellowship is awarded to individuals in the early stages of their graduate study, who intend to pursue research-based graduate studies in science, technology, engineering, and mathematics (STEM).
The program provides awardees with three years of financial support consisting of a $37,000 annual stipend and a $12,000 education allowance. UW–Madison contributes toward fringe benefits.
UW–Madison researchers key in search for neutrino emission from the brightest gamma-ray burst ever detected
On October 9th, 2022, an unusually bright pulse of high-energy radiation whizzed past Earth, captivating astronomers around the world. The luminous emission came from a gamma-ray burst (GRB), one of the most powerful classes of explosions in the universe. Named GRB 221009A, it triggered detectors at NASA’s Gamma-ray Burst Monitor and Large Area Telescope (both on board the Fermi Gamma-ray Space Telescope), the Neil Gehrels Swift Observatory, and the Wind spacecraft as well as other telescopes that quickly turned to the GRB site to study its aftermath.
Jessie Thwaites
This record-shattering GRB is one of the closest and the brightest GRB ever spotted, earning it the nickname BOAT (“brightest of all time”). This GRB is believed to come from an exploding star and likely signals the birth of a black hole.
In a new study by the IceCube Collaboration, published today in The Astrophysical Journal Letters, UW–Madison researchers presented results of one of five searches for neutrino emission from GRB 221009A that leveraged the full detector range, covering nine orders of magnitude in energy. Because no significant emission was found across samples spanning 10 MeV to 10 PeV, the results are the most stringent constraints on neutrino emission from GRBs.
As some of the most energetic sources in the universe, GRBs have long been considered a possible astrophysical source of neutrinos—tiny “ghostlike” particles that travel through space and large amounts of matter unhindered. These high-energy neutrinos are of particular interest to the National Science Foundation-supported IceCube Neutrino Observatory, a gigaton-scale neutrino detector at the South Pole.
IceCube is run by the international IceCube Collaboration, which comprises over 350 scientists from 58 institutions around the world. The Wisconsin IceCube Particle Astrophysics Center (WIPAC), a research center at UW–Madison, is the lead institution for the IceCube project.
Previously, IceCube has performed searches for neutrino emission from GRBs, but thus far, a correlation has not been found between high-energy neutrinos and GRBs. The recent observation of GRB 221009A presented IceCube with the best opportunity yet to search for neutrino emission by GRBs.
Justin Vandenbroucke
“Not only was this GRB the brightest ever detected in gamma rays, it also occurred in a region of the sky where IceCube is very sensitive,” says UW–Madison physics professor Justin Vandenbroucke, who helped lead the analysis.
For the study, collaborators carried out five complementary IceCube analyses that encompassed the full energy range of the detector. Each analysis targeted a specific energy range, with the idea of covering as wide an energy range as possible. UW–Madison physics PhD student Jessie Thwaites was one of the main analyzers.
Thwaites performed a “fast response” analysis based on real-time data from the South Pole to search for high-energy (0.10 teraelectronvolts to 10 petaelectronvolts) neutrinos from the direction of the GRB. They chose two time windows: one three-hour window covering all of the triggers reported in real time, and one covering two days. Their analysis, which set strong constraints on neutrino emission from GRBs, was quickly reported to the community, within hours of the GRB being detected by the gamma-ray satellites.
“In the high energies, our upper limits are very constraining—they are below the observations from gamma-ray telescopes,” says Thwaites. “These upper limits, combined with the observations from many electromagnetic telescopes, give us more information about GRBs as potential particle accelerators.”
Because this GRB is so bright, and because it has been so well studied, IceCube is able to place constraining upper limits on neutrino emission models proposed for this specific GRB. These constraints will enable better understanding of how GRBs work.
The collaborators are already developing new methods to improve searches for neutrinos from GRBs and other transient astrophysical sources. In addition, future upgrades and proposed extensions of IceCube, including the IceCube Upgrade project and IceCube-Gen2, could be the key to finding high-energy neutrino emission from GRBs or other transients.
According to Vandenbroucke, “This GRB illustrates the capabilities of IceCube for real-time follow-up of astrophysical transients. IceCube views the entire sky, all the time, over a factor of a billion in energy range. There is likely a burst of neutrinos already flying towards us from some other cosmic source, and we are ready for it.”
+ info “Limits on Neutrino Emission from GRB 221009A from MeV to PeV using the IceCube Neutrino Observatory,” The IceCube Collaboration: R. Abbasi et al. Published in The Astrophysical Journal Letters. arxiv.org/abs/2302.05459
IceCube performs the first search for neutrinos from novae
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White dwarfs are very dense, compact objects that are one of the possibilities for the final evolutionary state of stars. If they happen to be in a binary system with another companion star, the white dwarf may pull material from the companion star onto its surface. In this case, if enough material is accumulated, a nuclear reaction may occur on the surface of the white dwarf, causing a luminous burst of photons called a nova. Historically, astronomers believed they were seeing stars being born, hence the name, although we now know that is not the case. In the past decade, GeV and even TeV gamma rays were discovered from novae, suggesting that neutrinos—neutral, nearly massless cosmic messengers—could originate from novae as well.
In a paper recently submitted to The Astrophysical Journal, the IceCube Collaboration presents its first search for neutrinos from novae using a subarray of the IceCube Neutrino Observatory, a gigaton-scale detector operating at the South Pole. Although significant emission from novae was not found, IceCube set the first observational upper limits on neutrino emission from novae.
According to Justin Vandenbroucke, professor of physics at the University of Wisconsin–Madison and one of the study leads, “Novae, the little cousins of supernovae, are one of the longest known types of astrophysical transient. The discovery that they produce gamma rays was a huge surprise. Our neutrino analyses are starting to add to the modern understanding of these historical phenomena.”
NASA’s Fundamental Physics Program has selected seven proposals, including one from UW–Madison physics professor Shimon Kolkowitz, submitted in response to the Research Opportunities in Space and Earth Sciences – 2022 Fundamental Physics call for proposal.
The selected proposals are from seven institutions in seven states, with the total combined award amount of approximately $9.6 million over a five-year period. Kolkowitz’s proposal is ““Developing new techniques for ultra-high-precision space-based optical lattice clock comparisons.”
Three of the selected projects will involve performing experiments using the Cold Atom Laboratory (CAL) aboard the International Space Station (ISS). Four of the selected proposals call for ground-based research to help NASA identify and develop the foundation for future space-based experiments.
The Fundamental Physics Program is managed by the Biological and Physical Sciences Division in NASA’s Science Mission Directorate. This program performs carefully designed research in space that advances our understanding of physical laws, nature’s organizing principles, and how these laws and principles can be manipulated by scientists and technologies to benefit humanity on Earth and in space.
