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Astrophysicist Roger Ulrich Honored for Unlocking New Ways of Peering Inside our Sun

Roger Ulrich, Ph.D. Photo credit: Nils Lund, Kavli Prize.

Astrophysicist Roger Ulrich, Ph.D., has spent decades probing the inner workings of the Sun. In fact, he was the first to make precise measurements of what is happening in the Sun’s interior by observing oscillations on the solar surface. By 1960, researchers, Ulrich among them, had observed that the Sun’s surface oscillates a few kilometers every five minutes. Ulrich calculated the structure of these ongoing oscillations, or solar quakes.

I thought that was a really interesting prospect that we'd be able to learn something about the material below the visible surface of the Sun,” he says.

Using a similar principle to how geophysicists learn about the earth’s interior by examining the motions of waves made by earthquakes, Ulrich used mathematical models to analyze the Sun’s vibrations. Ulrich’s research goes beyond understanding the interior of our Sun. Solar physicists also use his findings to address threats and solve challenges here on Earth. Space weather forecasts, for example, help with the prediction of solar storms, solar flares, and coronal mass ejections. These events can damage the many satellites people depend on for communication, navigation and the stability of our power grid, while also monitoring solar storm radiation which can be dangerous to astronauts.

His work formed the foundation of a new field of solar physics, helioseismology, known as asteroseismology when referencing all stars. Ulrich showed the Sun behaves like an organ pipe, with many different acoustic waves at different frequencies. These discoveries led Ulrich to winning the prestigious 2022 Kavli Prize in astrophysics. “It certainly was a surprise. The work that the prize is rewarding was done back in 1970, so it's a long time in the past,” notes Ulrich, now a University of California, Los Angeles (UCLA) professor emeritus of astronomy and physics.

Ulrich shares the Kavli honor with Belgian astrophysicist Conny Aerts, Ph.D., and Danish astrophysicist Jørgen Christensen-Dalsgaard, Ph.D. The Norwegian Academy of Science and Letters, a sponsor of the Kavli Prize, says their work on stellar vibrations “has laid the foundations of solar and stellar structure theory, and revolutionized our understanding of the interiors of stars.”

The tools needed to make advances in helioseismology are expensive, and include components of finance, politics, and international diplomacy as well as the science itself for researchers. Be it telescopes, satellites, or precision instruments, design and deployment often involve several countries, space agencies, and highly competitive research projects. Ulrich remembers how meetings involving the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) could get heated at times because of the high stakes involved.

"It was intense, and we were the new kids on the block, so to speak, and I had to try and justify why we needed the kind of data that we'd need,” remembers Ulrich.  “It turns out that the telemetry requirements to do a proper helioseismic experiment are quite demanding, and consequently somewhat expensive. So, when it came to discussing how that was going to be managed, I had to get up and explain, well, why do you need all that data? Why can't you do just with the low telemetry stuff?”

He recalled one meeting when a frustrated participant took off a shoe and banged it on the table in frustration with problems in the division of resources.

Ulrich and his team eventually got two experiments included into the joint NASA-ESA project: the Solar and Heliospheric Observatory. This mission was launched in 1995 to study the Sun from its core to the outer corona.

Helioseismology is now a key part of the study of the origination of magnetic fields during our Sun’s 11-year sunspot cycle. One direct application is the tracking of sunspots and their related active regions on the far side of the Sun. Sunspots can often spawn into those solar flares or coronal mass ejections that can make things dicey for electronics here at Earth.

Scientists are also looking ahead to some very long-range plans for space exploration and our understanding of other stars. Stellar activity is relevant to potential development of life on exoplanets. Ulrich says none of that knowledge is possible without measurements of interior dynamics enabled by helioseismology, adding: “Helioseismology makes our understanding of what is happening in the Sun more complete, so it aids in all these efforts.”

Ulrich’s passion for space goes back to a planetarium he set up in a closet as a kid, made from a photocopied Norton Star Atlas and precisely located pin pricks in black construction paper. It was clever enough to win third place in the San Francisco Science Fair. His father was a plant nutrition specialist, and his mother, a forestry expert, so it seemed likely science would be in his future. Ulrich studied chemistry at the University of California Berkeley and fondly remembers hanging out at his father’s lab, playing with Monroe and Marchant calculator machines. Eventually his “hobby” of astrophysics won over chemistry for his graduate studies.

Since his retirement from UCLA in 2008, Ulrich still has many projects tied to his observational work at the Mount Wilson Observatory near Pasadena, California. He has made many improvements to the facility, which he managed from 1985-2012, and is currently working with data from a 150-foot solar tower telescope dating back to 1967.

“It's actually the earliest available data on the solar magnetic fields and the solar rotation and other flow patterns that we see in the Doppler signal. I've been working with that, trying to understand what happened during those decades of observation. The other data streams that are out there now are not that long so there's still some unique stuff that I can try and do with this old data, and I'm trying to work on it,” he says.

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Marsha Walton

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