Fermi Bubbles: Giant, Multibillion-Year-Old Reservoirs of Galactic Center Cosmic Rays

Recently evidence has emerged for enormous features in the gamma-ray sky observed by the Fermi-LAT instrument: bilateral ''bubbles'' of emission centered on the core of the Galaxy and extending to around +/- 10 kpc from the Galactic plane. These structures are coincident with a nonthermal microwave ''haze'' and an extended region of x-ray emission. The bubbles' gamma-ray emission is characterized by a hard and relatively uniform spectrum, relatively uniform intensity, and an overall luminosity 4 x 10(37) erg/s, around 1 order of magnitude larger than their microwave luminosity while more than order of magnitude less than their x-ray luminosity. Here we show that the bubbles are naturally explained as due to a population of relic cosmic ray protons and heavier ions injected by processes associated with extremely long time scale (greater than or similar to 8 Gyr) and high areal density star formation in the Galactic center.