Crab Nebula's Gamma-Ray Flare Mystifies Astronomers

The Crab Nebula has shocked astronomers by emitting an unprecedented blast of gamma rays, the highest-energy light in the Universe. The cause of the 12 April gamma-ray flare, described at the Third Fermi Symposium in Rome, is a total mystery. It seems to have come from a small area of the famous nebula, which is the wreckage from an exploded star. The object has long been considered a steady source of light, but the Fermi telescope hints at greater activity.

The gamma-ray emission lasted for some six days, hitting levels 30 times higher than normal and varying at times from hour to hour. While the sky abounds with light across all parts of the spectrum, Nasa's Fermi space observatory is designed to measure only the most energetic light: gamma rays. At the heart of the brilliantly coloured gas cloud of the Crab Nebula we can see in visible light, there is a pulsar - a rapidly spinning neutron star that emits radio waves which sweep past the Earth 30 times per second. But so far none of the nebula's known components can explain the signal Fermi sees.

Mysterious Structures Balloon from Galaxy's Core

Two huge bubbles that emit gamma rays have been found billowing from the center of the Milky Way galaxy, astronomers have announced. The previously unseen structures, detected by NASA's Fermi Gamma-ray Space Telescope, extend 25,000 light-years north and south from the galactic core. For now the source of all that energy is unclear, said study co-author Doug Finkbeiner, an associate professor of astronomy at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.

The newfound bubbles are made of hot, charged gas that's releasing the same amount of energy as a hundred thousand exploding stars. One possible answer is that the gamma-ray bubbles are evidence of an ancient burst of star formation at the center of the galaxy. If a huge cluster of massive stars formed millions of years ago, the giants could now be dying together, creating an outbreak of supernovae. "Another hypothesis, which is perhaps even more dramatic, is that the [mostly dormant] black hole at the center of the galaxy is active for a little bit," he said.