What are Blazars?
For most people they have only heard of cool space terms like black holes, supernovas or maybe even quasars. Well blazar isn’t a common term you’ll hear a lot and it’s actually not very different from a quasar. The picture above is essentially a blazar. It has an intensely bright central nucleus (or part of a classification called “active galactic nuclei” or AGN) containing a supermassive black hole. What’s really crazy about blazars is that the emitted light which sometimes includes extremely high energy gamma rays, can be over a hundred million times more energetic than the highest energy X-rays that the Chandra X-ray Observatory can study. Now just imagine a swirling disk filled with massive amounts of energy. We are talking about high energy gamma rays shooting out at 99% the speed of light! Also to make you feel even more uneasy, blazars are viewed with the barrel aiming right at Earth. It’s usually the down jet pointing towards Earth but most of these are so far away that they can’t harm us. The jets are interesting as the beam is shot out by a combination of intense magnetic fields and powerful winds from the accretion disk.The overall emission has several other unique properties as well, including that its intensity can vary dramatically with time.
Astronomers suspect that this bizarre behavior results when matter falling onto the vicinity of the massive black hole erupts into powerful, narrow beams of high velocity charged particles. The intense X-ray and gamma ray emission we see, and the variability as well, are thought to be the results of our fortuitously staring right down the throats of such cosmic monsters. But blazars are among the rarest of active nuclei, with only about 2700 known, and the physical processes that trigger and sustain such jets are still not known. Although relatively few, their powerful emissions make them major contributors to the overall picture of the cosmos.
The recently launched NASA Wide Infrared Survey Explorer (WISE) satellite has just completed an infrared survey of the whole sky in four infrared colors. The astronomers matched galaxies known to be blazars with objects measured by WISE in regions of the sky where the data have been reduced and made public. In a new paper in The Astrophysical Journal, the team report their discovery that the infrared bands are remarkably effective at finding blazars. Ninety-seven percent of known blazars were easily picked out from thousands of other WISE sources because their colors in the infrared are different from the colors of other kinds of galaxies. In most galaxies the infrared radiation comes from dust, heated either by star formation or ultraviolet radiation from the vicinity of the massive black hole. In a blazar, however, a completely different mechanism is apparently at work: the ejected beam of charged particles, moving in a powerful magnetic field at nearly the speed of light, radiates infrared light of a distinctly different color than dust emission.
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| structure of a blazar |
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