Every 3.4 years, pulsar B1259-63 dives twice through the gas disk surrounding the massive blue star it orbits. With each pass, it produces gamma rays. During the most recent event, NASA's Fermi Gamma-ray Space Telescope observed that the pulsar's gamma-ray flare was much more intense the second time it plunged through the disk. Astronomers don't yet know why.
This diagram, which illustrates the view from Earth, shows the binary's anatomy as well as key events in the pulsar's recent close approach. No Labels. Credit: NASA/Goddard Space Flight Center/Francis Reddy