A decade’s worth of telescope observations of the sun have revealed a startling mystery: Gamma rays, the highest frequency waves of light, radiate from our nearest star seven times more abundantly than expected. Stranger still, despite this extreme excess of gamma rays overall, a narrow bandwidth of frequencies is curiously absent.
The surplus light, the gap in the spectrum, and other surprises about the solar gamma-ray signal potentially point to unknown features of the sun’s magnetic field, or more exotic physics.
“It’s amazing that we were so spectacularly wrong about something we should understand really well: the sun,” said Brian Fields, a particle astrophysicist at the University of Illinois, Urbana-Champaign.
The unexpected signal has emerged in data from the Fermi Gamma-ray Space Telescope, a NASA observatory that scans the sky from its outpost in low-Earth orbit. As more Fermi data have accrued, revealing the spectrum of gamma rays coming from the sun in ever-greater detail, the puzzles have only proliferated.