Gamma rays produced via thermonuclear fusion in the Sun’s core are absorbed long before they reach the visible surface, or photosphere. Nonetheless, our neighborhood star glows brightly in the gamma-ray spectrum due to interactions with cosmic rays: Speedy protons passing through the solar system smash into the photosphere and unleash cascades of particles and high-energy radiation.
Theorists have struggled to model how the incoming cosmic rays and the solar magnetic fields that steer them produce the Sun’s observed gamma-ray spectrum. New measurements from the Fermi Gamma-Ray Space Telescope’s Large Area Telescope offer the best-ever look at the Sun’s gamma emissions—and reveal that theorists still have a lot of work to do.
Analyzing data collected between August 2008 and November 2017, Tim Linden of the Ohio State University and his colleagues charted gamma-ray events by their energy and their position on the solar disk. Throughout the observing period, Fermi detected...
