Gamma Ray Blazars: Jets from Super Massive Black Holes in Galactic Nuclei

The gamma-ray sky is illuminated by blazars that flicker wildly from month to month or even hour to hour. These are the centers of galaxies where black holes with masses as high as billions of suns are accreting magnetized, ionized gas from their surroundings. A tiny fraction of the particles in the gas escape along the poles to make narrow jets that flow out of the galaxy at near-light speeds. The Fermi Gamma-ray Space Telescope has revolutionized our ability to study these fascinating objects. The gamma rays arise from energetic processes involving highly energetic charged particles that spiral in large-scale magnetic fields. Blazars often exhibit dramatic outbursts when the gamma-ray luminosity completely dominates that at lower frequencies. Ultra-high resolution images made with the Very Long Baseline Array at radio frequencies reveals that these events often occur in bright features that move down the jet at velocities that appear (through an illusion) to be faster than the speed of light.