The northern lights, towering luminescent swirls of bright colors, have long captured the imagination and wonder of many. And Jim Schroeder, assistant professor of physics at Wheaton College, is no exception. Unlike most awe-struck beholders who travel closer to the earth’s northern magnetic pole (in the months of January, February, and March) to witness the phenomenon, Schroeder has dedicated years of research to demystifying these heavenly lights. His efforts culminated on June 7, 2021, when Schroeder, alongside physics colleagues from the University of Iowa, University of California Los Angeles and the Space Science Institute, published an article explaining the processes behind the aurora borealis. The team’s groundbreaking research not only confirms the cause of the northern lights but finally answers the question of how the electrons that create the famous light show gain the necessary energy to crash down from space.
Schroeder’s paper represents the culmination of decades of scientific research on the connection between Alfvén waves and the northern lights. Alfvén waves are a type of electromagnetic wave found in magnetized plasma, which is a gas of ions and electrons that has a magnetic field going through it. The waves are named after Swedish physicist Hannes Alfvén, who in the 1930s was the first scientist to theorize the existence of this type of electromagnetic wave.
According to Schroeder, around the turn of the millennium scientists utilized two research satellites, the FAST satellite and the Polar satellite, to study the auroras, natural light displays found near the Earth’s magnetic poles in the Arctic Circle and Antarctica that spread vibrant waves of color across the sky. Both satellites at this time indicated that Alfvén waves exist above the northern lights.
Scientists had already concluded that the aurora borealis is created by electrons crashing down from outer space and running into the atmosphere, creating a visual display of blue, green, and purple light. But scientists remained uncertain about how these electrons acquired the necessary energy to crash from outer space. Many now wondered whether the recently-discovered Alfvén waves might offer an explanation.
“In the 1970s, several researchers put forth the hypothesis that the aurora were caused by electrons that were accelerated by Alfvén waves generated during geomagnetic storms,” said Dr. Gregory Howes, associate professor of physics and astronomy at the University of Iowa, and another member of the research team.
Howes explained that in the last 25 years, spacecraft measurements have been able to measure Alfvén waves at high altitudes descending towards the Earth, and at lower altitudes, physicists measured these accelerated electrons.
“The hypothesis for a long time has been that these electromagnetic waves give energy to the electrons and then the electrons come down and make auroras,” said Schroeder.
The difficulty had surrounded how to prove such a hypothesis. Schroeder’s team ultimately utilized the University of California at Los Angeles’ Basic Plasma Science Facility to prove that electromagnetic Alfvén waves propel electrons moving through the earth’s magnetic field, ultimately producing auroras as the fast-moving electrons crash into the atmosphere’s oxygen and nitrogen molecules.
Confirming such a discovery has not been a simple endeavor.
“The experiment started over twenty years ago when University of Iowa Professor Craig Kletzing initiated a collaboration with the experimentalists at UCLA on the Large Plasma Device (LAPD) to try to demonstrate in the lab the hypothesis that Alfvén waves accelerate the electrons the lead to the aurora during geomagnetic storms,” said Howes, who developed the experiment’s field-particle correlation technique that allowed the team of physicists to conjoin the measurements made at UCLA and predictions of the theory of Alfvén wave electron surfing.
Over the course of those twenty years, from the late 1990s to 2021, a variety of individuals have been immersed and contributed to the research, including university faculty, postdoctoral researchers, and graduate students. Through the ongoing project, six young scientists have been trained and continued as professionals in science, taking positions as research scientists or faculty members.
Schroeder, who now teaches “Computer Modeling” and “Analog Electronics” at Wheaton, first joined the project at UCLA’s Basic Plasma Science Facility in 2012, as a graduate student at the University of Iowa. In 2017, during his postdoctoral research, Schroeder designed the Alfvén wave experiments conducted at UCLA. The experiments were funded by various agencies, including the Department of Energy, the National Science Foundation, and NASA. Data was collected at UCLA’s Basic Plasma Science Facility using their “Large Plasma Device,” or LAPD.
According to Schroeder, the LAPD is a cylindrical vacuum chamber full of a tube of plasma.
“Inside of the LAPD vacuum chamber they’ll put a little puff of gas that spreads out really quickly into the low pressure,” said Schroeder. “Then they’ll run electricity through it to make plasma which is a gas electrons have been broken off of the atoms.”
Through this process within the LAPD, electromagnetic Alfvén waves are created. Schroeder’s team focused their attention on the manner in which the plasma’s electrons respond to Alfvén waves.
“The goal was to see if electrons gain energy from the waves in a way that would allow the electrons to make auroras, or northern lights,” said Schroeder.
The project proved that electrons did in fact gain energy from those waves. The research team’s main discovery revolved around a process known as Landau damping, which Schroeder described as electrons “surfing on the waves.”
“In the plasma we found that only the electrons that were close to the speed of the wave are the ones that get picked up and accelerated, kind of like surfing,” said Schroeder. “And so what we were able to show is that Alfvén waves give energy to electrons in a way that would allow the electrons to make auroras.”
According to Howes, the variations in which electrons acquire energy as a function of their velocity within the LAPD, which created Alfven waves, proved the “surfing” phenomenon true.
Work at UCLA concluded in May 2018, after the final successful experiment was conducted at the lab, proving that electrons indeed are accelerated by electromagnetic Alfvén waves.
From 2018 to 2021, careful data analysis and then peer review processes on the research article were underway. Schroeder completed his time as a postdoctoral research scholar at the University of Iowa during this time period. He moved to Wheaton to begin teaching in the physics department, while simultaneously completing much of the necessary data analysis and writing the research paper itself.
Since the research paper’s publication this summer, Schroeder explained that scientists in the field of laboratory plasma astrophysics have been especially excited by the new discovery. And since its publication two months ago, the article has been accessed over 8,000 times on the Nature Communications website. Schroeder himself, as a result of his work on the project, has been invited to eight different talks at institutions around the United States to present and discuss his research findings.
Despite all the acclaim he’s received, for Schroeder the publication of his research fulfilled a more personal interest. Schroeder’s longtime fascination with the lights just beyond our reach has come full circle. For Schroeder, the movement from admiration and curiosity to tinkering in order to understand the scientific world has been interwoven throughout his story. From a child admiring the night sky to a professional with groundbreaking research to his name, Schroeder has fulfilled a childhood dream.
“The expanse of space and the beauty of space has always captured me. When I learned that there were some questions about the northern lights that we were still trying to figure out, that really got me hooked. I wanted to do that,” said Schroeder. “It’s been something that has constantly motivated me to try to understand the beauty of the Northern Lights a little bit better.”
