A few months ago, researchers with NASA’s Fermi Gamma-ray Space Telescope reported that they’d detected gamma rays from several classical novae. These thermonuclear eruptions happen on the surfaces of white dwarfs that are guzzling too much gas off a companion star.
The gamma rays baffled researchers: classical novae shouldn’t produce these high-energy photons. Gamma rays come from particles accelerated at shock fronts. That implies that stuff in the burst’s outflow is slamming into other stuff in the outflow. But there was no good explanation for why the ejecta would do that.