An Unexpected Flare from the Crab Nebula

Explanation: Why does the Crab Nebula flare? No one is sure. The unusual behavior, discovered over the past few years, seems only to occur in very high energy light -- gamma rays . As recently as one month ago, gamma-ray observations of the Crab Nebula by the Fermi Gamma Ray Space Telescope showed an unexpected increase in gamma-ray brightness, becoming about five times the nebula's usual gamma-ray brightness, and fading again in only a few days. Now usually the faster the variability, the smaller the region involved. This might indicate that the powerful pulsar at the center of the Crab , a compact neutron star rotating 30 times a second, is somehow involved. Specifically, speculation is centered on the changing magnetic field that surely surrounds the powerful pulsar . Rapid changes in this field might lead to waves of rapidly accelerated electrons which emit the flares , possibly in ways similar to our Sun . The above image shows how the Crab Nebula normally appears in gamma rays, as compared to the Geminga pulsar, and how it then appeared during the recent brightening.