March 9, 2026
Arthur H. Compton Lecture series will illuminate how researchers are harnessing the interactions of astroparticles to answer questions about our earth
Last month, a UChicago-led mission known as Payload for Ultrahigh Energy Observations, or PUEO, landed a few hundred miles from the South Pole after a 23 day journey on a NASA balloon. PUEO flew 120,000 feet above the ground on the hunt for some of the highest energy particles in the universe, neutrinos.
Signatures of these and other high-energy particles from outer space could give us information about some of the most violent events in the universe, such as super massive black holes or star explosions. They also have the potential to unlock mysteries closer to home about the core of our earth, lightning formation, and water on the moon.
In this spring’s Compton Lectures, Keith McBride, a UChicago postdoctoral researcher, will illuminate how these "messengers from the universe," or astroparticles, can answer questions about the farthest reaches of our universe as well as be harnessed as practical tools to understand our earth. The free public talks run every Saturday from March 28 through May 16 at 11 AM.
"We want to understand how these particles are getting here, where they're coming from, how old they are, and what they can tell us about their journey," said McBride.
Cosmic rays were first discovered in 1912 by Austrian physicist Victor Hess, who flew a balloon at 17,000 feet and discovered radiation coming from above Earth's atmosphere. This radiation was later named "cosmic rays" in 1925, when Nobel laureate and former UChicago faculty member Rober Millikan used the term in a paper.
These cosmic rays are charged particles that move extremely fast and are largely blocked by Earth's atmosphere. When cosmic rays strike our atmosphere or other dense materials, they create a shower of secondary particles.
“When they interact in the atmosphere, we can detect the energy they leave behind as particles called muons,” said McBride.
Similarly, high-energy neutrinos are secondary particles produced by cosmic rays interacting with gas or radiation in violent environments such as the remnants of supernovae. During PUEO's journey above Antarctica, the experiment used an array of antennas to detect signals of high-energy neutrinos colliding with atoms in the ice, an interaction that produces radio waves.
McBride, who led the development of major portions of the PUEO instrument, also worked on another balloon mission, the High-Energy Light Isotope eXperiment (HELIX), which landed in June 2024 after six days in space. HELIX was designed to study cosmic rays directly, using a superconducting magnet that would bend the particles so that researchers could measure their mass and identify isotopes, a method similar to carbon dating that helps determine the age of the particles.
During the Compton series, McBride will discuss how high-energy astroparticles like neutrinos and cosmic rays are not only helping us understand the universe but also helping us make measurements of extremely dense objects. Muons, for example, have been used to peer inside large structures like volcanoes and pyramids, and researchers are now using neutrinos to help understand the earth’s composition.
“Since neutrinos interact with dense materials, you can measure how many neutrinos have passed through the earth to potentially help us make a map of the core,” said McBride.
In another lecture in the series, McBride will discuss one of the leading theories about how lightning is formed.
“We know that lightning occurs when charged particles in the atmosphere go to ground. But what starts the charges moving in the first place?” said McBride. “Cosmic rays could be creating the seeds for lightning.”
Payton Linton, McBride’s collaborator and senior graduate student at The Ohio State University, will give a guest lecture on May 9, showcasing how a proposed lunar orbiter will use interactions of cosmic rays to help us detect ice beneath the moon's surface.
"What a lot of people don't realize is that particle physics has interdisciplinary applications. We can take what we've learned about astroparticles and their interactions to better understand the world around us," said McBride.
The free talks are held at the Kersten Physics Teaching Center, 5720 S. Ellis Ave., in Room 106, and will be broadcast online.