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Weekly Science Update

Wednesday, March 14, 2007
A Giant Quasar Jet
Quasars are galaxies with massive black holes at their cores around which vast amounts of energy are being radiated -- quasars are among the most powerful energy sources known. Streaming out from the center of about 10% of quasars, like cosmic laser beams, are powerful jets of electrons and other subatomic particles that travel at nearly the speed of light. Quasars are mysterious. No one knows for sure how they form, how they develop in time, or how their stupendous energies are produced. Because they are so bright, quasars can be seen even when they are very far away, and this combination of being both highly energetic and located at cosmological distances makes quasars interesting to astronomers who are trying to better understand both the nature of black holes (our own Galaxy has one at its center) and the conditions in the early universe that prompt these monsters to form.

The jets streaming from the regions around black holes typically emit in a wide range of wavelengths, including X-ray wavelengths. SAO astronomers Aneta Siemiginowska and Daniel Harris, along with five colleagues, used the Chandra X-ray Observatory to study one of the longest known X-ray jets. Stretching across about one million light-years -- far longer than the diameter of the Milky Way galaxy -- the jet comes from the center of a quasar so distant that its light has been traveling towards us for 8.2 billion years, almost two-thirds of the age of the universe. The team finds that the jet looks sharply different at X-ray wavelengths than it does at radio wavelengths. From their analysis, the astronomers conclude that the simple models previously suggested for jets do not work: the X-rays appear to arise from the jet proper, while radio emission comes from a different region, a surrounding jet "sheath." Furthermore, there is evidence for intermittent jet activity that produces knots and other structures. The new results not only help to understand what is going on in this dramatic case, they also suggest that similar processes may in fact be at work in many quasar jets.

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