Gamma
Haze
Gamma rays have as much energy as you can pack into a photon,
and it takes something cataclysmic to make a lot of them: a giant star exploding
, matter being ripped as it falls into a black hole-that sort of thing. But
astronomers recently discovered a faint gamma-ray glow surrounding our galaxy-a
glow they are at a loss to explain. David Dixon, a physicists at the University
of California at Riverside, discovered the glow while studying data from a NASA
satellite, the Compton Gamma Ray Observatory.
"We
subtracted the gamma rays caused by cosmic rays interacting with the interstellar
matter," Dixon says, "as well as a uniform glow found all over the
sky. We expected to see just point sources like pulsars and active galaxies."
Instead, after even more subtle image processing, they were left with some 10
percent of the total glow that seems to come from just outside the galaxy. The
gamma haze shown in this map of the Milky Way could come from low-energy photons
that smack into high-speed electrons escaping the galaxy or perhaps from a population
of small, dim pulsars in the galactic halo. It could even be the signature of
the annihilation of never-before-seen particles that might account for much
of the mass of the universe. A new gamma-ray satellite, scheduled for launch
in 2000, may put the mystery to rest.