UMD Scientists Help Discover the Highest-Energy Light Coming from the Sun

Sometimes, the best place to hide a secret is in broad daylight. Just ask the sun.

A new paper in Physical Review Letters details the discovery of the highest-energy light ever observed from the sun. The international team behind the discovery also found that this type of light, known as gamma rays, is surprisingly bright. That is, there’s more of it than scientists had previously anticipated.

Watching like a HAWCA figure that looks like a heat map shows a bright yellow spot at its center, ringed by “cooler” oranges and purples. This represents the excess of gamma rays observed by the HAWC Collaboration.What an excess of solar gamma rays looks like to the High-Altitude Water Cherenkov Observatory Collaboration, which includes researchers from the University of Maryland. Credit: Courtesy of the HAWC Collaboration

Although the high-energy light doesn’t reach the Earth’s surface (and thus is no threat to life), these gamma rays create cascades of particles that move at near the speed of light through the atmosphere. They were detected by an international group of scientists, including University of Maryland astrophysicists, using the High-Altitude Water Cherenkov Observatory, or HAWC.  

HAWC is an important part of the story. Unlike other observatories, it works around the clock observing more than 2/3 of the entire sky every day.

“HAWC has made numerous discoveries about very high energy gamma rays from exotic objects like supernova remnants, microquasars, and active galaxies, but this discovery comes from much closer to home – our own Sun,” says Jordan Goodman, UMD Distinguished University Professor and Principal Investigator for the HAWC project, which is funded by the National Science Foundation, the National Council of Humanities Science and Technology (CONACyT) of México, the U.S. Department of Energy, Los Alamos National Lab and the Max Planck Institute for Nuclear Physics in Heidelberg, 

“We now have observational techniques that weren’t possible a few years ago,” said Mehr Un Nisa, a postdoctoral research associate at Michigan State University and corresponding author of the new paper. 

“In this particular energy regime, other ground-based telescopes couldn’t look at the sun because they only work at night,” she said. “Ours operates 24/7.”

In addition to working differently from conventional telescopes, HAWC looks a lot different from the typical telescope.

Rather than a tube outfitted with glass lenses, HAWC uses a network of 300 large water tanks, each filled with about 200 metric tons of water. The network is nestled between two dormant volcano peaks in Mexico, more than 13,000 feet above sea level.

From this vantage point, it can observe the aftermath of gamma rays striking air in the atmosphere. Such collisions create what are called air showers, which are a bit like particle explosions that are imperceptible to the naked eye.

The energy of the original gamma ray is liberated and redistributed amongst new fragments consisting of lower energy particles and light. It’s these particles — and the new particles they create on their way down — that HAWC can “see.”

When the shower particles interact with water in HAWC’s tanks, they create what’s known as Cherenkov radiation that can be detected with the observatory’s instruments.

Nisa and her colleagues began collecting data in 2015. In 2021, the team had accrued enough data to start examining the sun’s gamma rays with sufficient scrutiny. The gamma rays lose energy in Earth’s atmosphere, meaning they don’t present a concern to life.

“After looking at six years’ worth of data, out popped this excess of gamma rays,” Nisa said. “When we first saw it, we were like, ‘We definitely messed this up. The sun cannot be this bright at these energies.’”

Making history

The sun gives off a lot of light spanning a range of energies, but some energies are more abundant than others.

For example, through its nuclear reactions, the sun provides a ton of visible light — that is, the light we see. This form of light carries an energy of about 1 electron volt, which is a handy unit of measure in physics.

The gamma rays that HAWC observed had about 1 trillion electron volts, or 1 tera electron volt, abbreviated 1 TeV. Not only was this energy level surprising, but so was the fact that they were seeing so much of it.

In the 1990s, scientists predicted that the sun could produce gamma rays when high-energy cosmic rays — particles accelerated by a cosmic powerhouse like a black hole or supernova — smash into protons in the sun. But, based on what was known about cosmic rays and the sun, the researchers also hypothesized it would be rare to see these gamma rays reach Earth.

At the time, though, there wasn’t an instrument capable of detecting such high-energy gamma rays and there wouldn’t be for a while. The first observation of gamma rays with energies of more than a billion electron volts came from NASA’s Fermi Gamma-ray Space Telescope in 2011.

Over the next several years, the Fermi mission showed that not only could these rays be very energetic, but also that there were about seven times more of them than scientists had originally expected. And it looked like there were gamma rays left to discover at even higher energies.

When a telescope launches into space, there’s a limit to how big and powerful its detectors can be. The Fermi telescope’s measurements of the sun’s gamma rays maxed out around 200 billion electron volts.

Theorists led by John Beacom and Annika Peter, both professors at Ohio State University, encouraged the HAWC Collaboration to take a look.

“They nudged us and said, ‘We’re not seeing a cutoff. You might be able to see something,” said Nisa.

The HAWC Collaboration includes more than 30 institutions across North America, Europe and Asia, and a sizeable portion of that is represented in the nearly 100 authors on the new paper. The University of Maryland team consists of Goodman, Research Scientist Andrew Smith, Project Engineer Michael Schneider and graduate students Kristi Engle, Elijah Wilox, Jason Fan, and Sohyoun Yun-Cárcamo.   

Now, for the first time, the team has shown that the energies of the sun’s rays extend into the TeV range, up to nearly 10 TeV, which does appear to be the maximum, Nisa said.

“This shows that HAWC is adding to our knowledge of our galaxy at the highest energies, and it’s opening up questions about our very own sun,” Nisa said. “It’s making us see things in a different light. Literally.”

 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.051201

 Original story courtesy of Michigan State University:https://msutoday.msu.edu/news/2023/surprising-sun-discovery


Lathrop Lab's Geodynamo Set for Overhaul

In a hangar-sized laboratory off Paint Branch Drive, Dan Lathrop gives the signal, and what he often calls simply “the experiment” awakens. A huge, steel sphere with tubes and electrical wires snaking across its surface begins a stately, nearly silent rotation inside a towering cage-like structure.

That’s the experiment running at visitor speed, however. When only Lathrop, a Distinguished Scholar-Teacher and professor in physics, and his graduate students are present to gather data, they crank up its 350 horsepower electric motor to spin 80 times faster, until the 3-meter globe encasing 25,000 pounds of liquid sodium blurs out at four revolutions per second.Professor Dan Lathrop examines the 3-meter steel sphere he uses in simulations of the Earth's "geodynamo." Hidden inside the spinning outer sphere (diagram, below) molten sodium and an even quicker-whirling inner sphere represent the earth's liquid outer core and solid inner core, which create geomagnetism. (Photo by John T. Consoli; diagram by Kolin Behrens)Professor Dan Lathrop examines the 3-meter steel sphere he uses in simulations of the Earth's "geodynamo." Hidden inside the spinning outer sphere (diagram, below) molten sodium and an even quicker-whirling inner sphere represent the earth's liquid outer core and solid inner core, which create geomagnetism. (Photo by John T. Consoli; diagram by Kolin Behrens)

For safety reasons, in the 11 years since he first switched the experiment on, no lab guest has ever watched it run that fast. Lathrop hasn’t either, exactly. “You can’t see it at full speed,” he said.

If “the experiment” sounds pretty singular, that’s because there’s nothing else like it on the planet. Lathrop, an expert in turbulent flows, envisioned the giant apparatus and several smaller predecessors as a way to simulate and perhaps even predict changes in the Earth’s magnetic field, which originates in its core and helps protect the surface from harmful solar radiation. While the machine has fascinated the geophysics community and generated useful results about planetary magnetic fields, it has never quite fulfilled Lathrop’s hopes. So this year, supported by a recently renewed National Science Foundation grant, he and his lab members will undertake a painstaking process to drain the flammable sodium, dismantle the device, upgrade it and—if the plan works—create a better magnetic model of the Earth.

Our planet has a “ggeodynamo diagrameodynamo,” a self-generating, self-sustaining magnetic field created by flows in its molten outer core, a layer of mostly iron and nickel more than 3,000 kilometers beneath our feet. Swirling turbulence in the liquid metal, caused by convection and the planet’s rotation, gives rise to electrical currents and magnetic fields that feed on each other.

So far, Lathrop’s experiment needs external current to generate a magnetic field; soon he hopes that will no longer be necessary. Doctoral students Rubén Rojas and Artur Perevalov in physics, along with Heidi Myers in geology and Sarah Burnett in mathematics, have been researching ways to modify a hidden, inner sphere of the device—analogous to Earth’s solid inner core—by adding texture to create swirling, helical flows in the highly conductive liquid sodium, generating electrical currents.

It’s never been tried before, so the results are hard to predict.

“I try not to be a foolish optimist, but you know, you aren’t going to build an experiment like this without a certain amount of optimism that there are interesting things to see,” Lathrop said.

The biggest potential prize would be an ability to predict the “weather” of Earth’s magnetic field, which is constantly in flux. Geologic evidence suggests the poles have reversed hundreds of times—most recently 780,000 years ago—and indeed, the North Pole has been moving from Canada toward Russia with increasing speed in recent years. During such a flip, much of the planet’s surface could have a weaker magnetic shield from solar radiation. (For a preview of what that could be like, look at Mars, which lacks a geodynamo.)

Even now, solar storms do create problems on Earth, damaging satellites and sensitive electronics, said Sara Gibson, a solar physicist at the National Center for Atmospheric Research in Boulder, Colo. For instance, if a massive 1859 solar storm that caused aurora as far south as the tropics hit today, it could fry communications and electrical grids worldwide.

“Dan’s work is really important, because it’s vital to understand the Earth’s magnetic field, which is coupling with what’s coming from the sun, and creating these magnetic impacts,” Gibson said.

Lathrop doesn’t promote his research with disaster scenarios. A pole reversal may not be in the offing at all, and would take more than 1,000 years. But what about scientific curiosity as well as simple prudence concerning a factor that allowed life to arise on earth?

“You think you’d want a solid scientific base knowing, well, how does it work, and how did it get there?” he said. “Where’s it at now? And where’s it going?”

Original story by Chris Carroll, Maryland Today 

Watch the 3 meter experiment.

Catching New Patterns of Swirling Light Mid-flight

In many situations, it’s fair to say that light travels in a straight line without much happening along the way. But light can also hide complex patterns and behaviors that only a careful observer can uncover.

This is possible because light behaves like a wave, with properties that play a role in several interesting phenomena. One such property is phase, which measures where you are on an undulating wave—whether you sit at a peak, a trough or somewhere in between. When two (otherwise identical) light waves meet and are out of phase, they can interfere with one another, combining to create intricate patterns. Phase is integral to how light waves interact with each other and how energy flows in a beam or pulse of light.

Researchers at the University of Maryland, led by UMD Physics Professor Howard Milchberg, have discovered novel ways that the phase of light can form optical whorls—patterns known as spatiotemporal optical vortices (STOVs). In a paper published in the journal Optica on Dec. 18, 2019, the researchers captured the first view into these phase vortices situated in space and time, developing a new method to observe ultra-fast pulses of light.

Each STOV is a pulse of light with a particular pattern of intensity—a measure of where the energy is concentrated—and phase. In the STOVs prepared by Milchberg and his collaborators, the intensity forms a loop in space and time that the researchers describe as an edge-first flying donut: If you could see the pulse flying toward you, you would see only the edge of the donut and not the hole. (See leftmost image below, where negative times are earlier.) In the same region of space and time, the phase of the light pulse forms a swirling pattern, creating a vortex centered on the donut hole (rightmost image).Processed data showing the intensity forming a ring (left) and the phase forming the vortex (right) in a spatiotemporal optical vortex. The green arrow indicates the increase of the phase around the vortex. (Credit: Scott Hancock/University of Maryland)Processed data showing the intensity forming a ring (left) and the phase forming the vortex (right) in a spatiotemporal optical vortex. The green arrow indicates the increase of the phase around the vortex. (Credit: Scott Hancock/University of Maryland)

Milchberg and colleagues discovered STOVs in 2016 when they found structures akin to “optical smoke rings” forming around intense laser beams. These rings have a phase that varies around their edge, like the air currents swirling around a smoke ring. The vortices made in the new study are a similar but simpler structure: If you think of the original smoke ring as a bracelet made of beads, the new STOVs are like the individual beads.

The prior work showed that STOVs provide an elegant framework for understanding a well-known high-intensity laser effect—self-guiding. At high intensity, this effect occurs when a laser pulse, interacting with the medium it’s traveling through, compresses itself into a tight beam. The researchers showed that in this process, STOVs are responsible for directing the flow of energy and reshaping the laser, pushing energy together at its front and apart at its back.

That initial discovery looked at how these rings formed around a beam of light in two dimensions. But the researchers couldn’t explore the internal working of the vortices because each pulse is too short and fast for previously established techniques to capture. Each pulse passes by in just femtoseconds—about a 100 trillion times quicker than the blink of an eye.

“These are not microsecond or even nanosecond pulses that you just use electronics to capture,” says Sina Zahedpour, a co-author of the paper and UMD physics postdoctoral associate. “These are extremely short pulses that you need to use optical tricks to image.”

To capture both the intensity and phase of the new STOVs, researchers needed to prepare three additional pulses. The first pulse met with the STOV inside a thin glass window, producing an interference pattern encoded with the STOV intensity and phase. That pattern was read out using two longer pulses, producing data like that shown in the image above.

“The tools we had previously only looked at the amplitude of the light,” says Scott Hancock, a UMD physics graduate student and first author of the paper. “Now, we can get the full picture with phase, and this is proof that the principle works for studying ultrafast phenomena.”

STOVs may have a resilience that is useful for practical applications because their twisting, screw-like phase makes them robust against small obstacles. For example, as a STOV travels through the air, parts of the pulse might be blocked by water droplets and other small particles. But as they continue on, the STOVs tend to fill in the small sections that got knocked out, repairing minor damage in a way that could help preserve any information recorded in the pulse. Also, because a STOV pulse is so short and fast, it is indifferent to normal fluctuations in the air that are comparatively slow.

“Controlled generation of spatiotemporal optical vortices may lead to applications such as the resilient propagation of information or beam power through turbulence or fog,” says Milchberg. “These are important for applications such as free-space optical communications using lasers or for supplying power from ground stations to aerial vehicles.”

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In addition to Milchberg, Zahedpour and Hancock, graduate student Andrew Goffin was a co-author.

This research was supported by the National Science Foundation (NSF) (Award No. 1619582), the Air Force Office of Scientific Research (Award Nos. FA9550-16-10121 and FA9550-16-10284) and the Office of Naval Research (Award Nos. N00014-17-1-2705 and N00014-17-12778). The content of this article does not necessarily reflect the views of the NSF, the Air Force Office of Scientific Research or the Office of Naval Research.

The paper “Free-space propagation of spatiotemporal optical vortices,” S. W. Hancock, S. Zahedpour, A. Goffin, and H. M. Milchberg was published in Optica on December 18, 2019.

Media Relations Contact: Bailey Bedford, 301-405-9401, This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Johnpierre Paglione Receives $1.55M from the Moore Foundation

Physics Professor Johnpierre Paglione has been awarded more than $1.5 million by the Gordon and Betty Moore Foundation to study the complex behavior of electrons in quantum materials.paglione jpJohnpierre Paglione

“The Moore Foundation has played a pivotal role in supporting and promoting quantum materials research over the last five years, and I am extremely excited to continue to be part of this effort,” said Paglione, who also directs UMD’s Quantum Materials Center (formerly the Center for Nanophysics and Advanced Materials).

The new grant was awarded by the Moore Foundation’s Emergent Phenomena in Quantum Systems (EPiQS) initiative, a quantum materials research program that funds work on materials synthesis, experiments, and theory, with an interdisciplinary approach that includes physicists, chemists, and materials scientists. EPiQS focuses on exploratory research that develop deep questions about the organizing principles of complex quantum matter, and it also supports progress toward new applications, like quantum computing and precision measurement. 

Paglione’s award for materials synthesis was one of only 13 in the U.S. and renews an earlier grant he received from EPiQS, which has provided more than $120 million to researchers since 2013.

“Fundamental studies of quantum materials play a critical role in not only supporting current development of quantum technologies, but also the discovery of new phenomena that hold promise for future applications,” Paglione said.

In recognition of that critical role, UMD’s Center for Nanophysics and Advanced Materials was renamed to the Quantum Materials Center (QMC) in October. The change emphasized the evolving interests of the Center’s members, and it was announced at a one-day symposium in September organized by Paglione and several colleagues.

“Our center’s purpose will remain focused on the fundamental exploration and development of advanced materials and devices using multidisciplinary expertise drawn from the physics, chemistry, engineering and materials science departments,” Paglione said. “But we will place strong emphasis on the pursuit of optimized and novel quantum phenomena with potential to nucleate future computing, information and energy technologies.”

The symposium brought together many local scientists who study quantum materials, including researchers from the university’s Departments of Physics, Chemistry and Biochemistry, Electrical and Computer Engineering, and Materials Science and Engineering, in addition to researchers from the National Institute of Standards and Technology (NIST) and the Laboratory for Physical Sciences. Amitabh Varshney, dean of UMD’s College of Computer, Mathematical, and Natural Sciences, and Robert Briber, associate dean of UMD’s A. James Clark School of Engineering, attended and shared their perspectives on campus initiatives in quantum science, including the newly formed Quantum Technology Center.

That meeting was bookended by several exciting research results from Paglione and his colleagues in the QMC. In June, they reported capturing the best evidence yet of Klein tunneling, a quantum quirk that allows electrons to burrow through a barrier like it’s not even there. The result, which was featured on the cover of the journal Nature, arises from a duo of quantum effects at the junction of two materials. One is superconductivity, which keeps electrons paired off in highly correlated ways. The other has to do with the precise kind of superconductivity present—in this case, topological superconductivity that further constrains the way that electrons interact with the interface between the two materials. In a nutshell, electrons heading toward the junction aren’t allowed to reflect back, which leads to their perfect transmission.

In August, Paglione and his collaborators published a paper in the journal Science about a new, unconventional superconductor. That material—uranium ditelluride—may also exhibit some effects expected of a topological superconductor, including a demonstrated resilience to magnetic fields that typically destroy superconductivity. One of the paper’s co-authors, NIST scientist and Adjunct Associate Professor of Physics Nicholas Butch, called the material a potential “silicon of the quantum information age,” due to its stability and potential use as a storage medium for the basic units of information in quantum computers.

In a follow-up paper published in the journal Nature Physics in October, many of the same researchers teamed up with scientists from the National High Magnetic Field Laboratory to test the properties of uranium ditelluride under extreme magnetic fields. They observed a rare phenomenon called re-entrant superconductivity, furthering the case that uranium ditelluride is not only a profoundly exotic superconductor, but also a promising material for technological applications. Nicknamed “Lazarus superconductivity” after the biblical figure who rose from the dead, the phenomenon occurs when a superconducting state arises, breaks down, then re-emerges in a material due to a change in a specific parameter—in this case, the application of a very strong magnetic field.

“This is indeed a remarkable material and it’s keeping us very busy,” Paglione said. “Uranium ditelluride may very well become the ‘textbook’ spin-triplet superconductor that people have been seeking for dozens of years and, more importantly, may be the first manifestation of a true intrinsic topological superconductor with potential for all sorts of technologies to come!”

Written by Chris Cesare with contributions from Matthew Wright

Galactic Gamma-ray Source Map Reveals Birthplaces of High-energy Particles

Nine sources of extremely high-energy gamma rays have been identified in a new catalog compiled by researchers with the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, including nine University of Maryland physicists. All nine sources produce gamma rays with energies over 56 trillion electron volts (TeV)—more than eight times the energy of the most powerful proton beams produced at particle accelerators on Earth—and three emit gamma rays extending to 100 TeV and beyond, making these the highest-energy sources ever observed in our galaxy. The catalog helps to explain where the particles originate and how they are produced with such extreme energies.hawc 2020The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory was used to create a map of the galactic plane indicating the highest energy gamma ray sources yet discovered. (Credit: Jordan Goodman/University of Maryland)

“The very high-energy gamma rays we detect are produced by interactions of even higher energy charged particles near their source,” said Jordan Goodman, a Distinguished University Professor of Physics at UMD and U.S. lead investigator and spokesperson for the HAWC collaboration.  “Charged particles are bent in the magnetic fields of our galaxy and don’t point back to their origin. Gamma rays, like light, travel in straight lines allowing us to use them to map the sources of the high-energy emission. HAWC, which is a wide field-of-view instrument, views the overhead sky 24/7 giving us a deep exposure to look for the rare high energy gamma ray events.”

The catalog of high-energy sources was published online in the journal Physical Review Letters on Jan. 15, 2020.  Higher-energy astrophysical particles have previously been detected, but this is the first time specific galactic sources have been pinpointed for such high-energy particles. All of the sources have extremely energetic pulsars nearby. The number of sources detected may indicate that ultra-high-energy emission is a generic feature of powerful particle winds coming from pulsars embedded in interstellar gas clouds known as nebulae, and that more detections will be forthcoming.

The HAWC Gamma-Ray Observatory consists of an array of water-filled tanks sitting high on the slopes of the Sierra Negra volcano in Puebla, Mexico, where the atmosphere is thin and offers better conditions for observing gamma rays. When gamma rays strike molecules in the atmosphere they produce showers of energetic particles. Nothing can travel faster than the speed of light in a vacuum, but in water light moves a little slower. As a result, some particles in cosmic ray showers travel faster than light in the water inside the HAWC detector tanks. The faster-than-light particles, in turn, produce characteristic flashes of light called Cherenkov radiation. Using recordings of the Cherenkov flashes in the HAWC water tanks, researchers reconstruct the sources of particle showers and learn about the particles that caused them.

The HAWC collaborators plan to continue searching for the sources of high-energy cosmic rays. By combining their data with measurements from other types of observatories, such as neutrino, X-ray, radio and optical telescopes, they hope to elucidate the astrophysical mechanisms that produce the cosmic rays that continuously rain down on our planet.

“There are still many unanswered questions about cosmic-ray origins and acceleration,” said Kelly Malone, an astrophysicist in the Neutron Science and Technology group at Los Alamos National Laboratory and a member of the HAWC scientific collaboration. “High energy gamma rays are produced near cosmic-ray sites and can be used to probe cosmic-ray acceleration. However, there is some ambiguity in using gamma rays to study this, as high-energy gamma rays can also be produced via other mechanisms, such as lower-energy photons scattering off of electrons, which commonly occurs near pulsars.”

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In addition to Goodman, other UMD co-authors from the Department of Physics included Visiting Professor Robert Ellsworth; Principal Engineer Michael Schneider; Research Scientist Andrew James Smith; Graduate Students Kristi Engel and Elijah Job Tabachnick; and Postdoctoral Associates Colas Rivière, Chad Brisbois and Israel Martinez-Castellanos.

Text for this news item was adapted with permission from a press release written by Los Alamos National Laboratory. 

The paper “Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC,” A.U. Abeysekara, et al. was published in Physical Review Letters on January 15, 2020.

The National Science Foundation, the U.S. Department of Energy and Los Alamos National Laboratory provided funding for the United States’ participation in the HAWC project. The Consejo Nacional de Ciencia y Tecnología (CONACyT) is the primary funder for Mexican participation. The content of this article does not necessarily reflect the views of these organizations.  

Media Relations Contact: Bailey Bedford, 301-405-9401, This email address is being protected from spambots. You need JavaScript enabled to view it.