Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2010 March 18
See Explanation.
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Fermi Catalogues the Gamma-ray Sky
Credit: NASA, DOE, International Fermi LAT Collaboration

Explanation: What shines in the gamma-ray sky? The most complete answer yet to that question is offered by the Fermi Gamma-ray Space Telescope's first all-sky catalogue. Fermi's sources of cosmic gamma-rays feature nature's most energetic particle accelerators, ultimately producing 100 MeV to 100 GeV photons, photons with more than 50 million to 50 billion times the energy of visible light. Distilled from 11 months of sky survey data using Fermi's Large Area Telescope (LAT), the 1,451 catalogued sources include energetic star burst galaxies and active galactic nuclei (AGN) far beyond the Milky Way. But within our own galaxy are many pulsars (PSR) and pulsar wind nebulae (PWN), supernova remnants (SNR), x-ray binary stars (HXB) and micro-quasars (MQO). Fermi's all sky map is shown centred on the Milky Way with the diffuse gamma-ray emission from the Galactic plane running horizontally through the frame. To locate the catalogued gamma-ray sources, just slide your cursor over the map. For now, 630 of the sources catalogued at gamma-ray energies remain otherwise unidentified, not associated with sources detected at lower energies.

Tomorrow's picture: winged things

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