The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays

Abstract

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 above and below the Galactic plane. These structures are coincident with a non-thermal microwave `haze' found in WMAP data and an extended region of X-ray emission detected by ROSAT. The bubbles' gamma-ray emission is characterised by a hard and relatively uniform spectrum, relatively uniform intensity, and an overall luminosity ~4 x 10^37 erg/s, around one 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 timescale (>~8 Gyr) and high areal density star-formation in the Galactic center.

arXiv commentAccepted for publication in Phys.Rev.Lett. 4 pages, 2 figures, brief textual revisions, conclusions unchanged

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