Fermi's Gamma Ray Sky (IMAGE) NASA/Goddard Space Flight Center Caption This animation switches between two images of the gamma-ray sky as seen by Fermi's Large Area Telescope (LAT), one using the first three months of LAT data, the other showing a cumulative exposure of seven years. The blue color, representing the fewest gamma rays, includes the extragalactic gamma-ray background. Blazars make up most of the bright sources shown (colored red to white). With increasing exposure, Fermi reveals more of them. A new study shows blazars are almost completely responsible for the background glow. Credit NASA/DOE/Fermi LAT Collaboration Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.