Weekly Science Update

Friday, October 24, 2008
X-ray Jets
The longest known collimated structures in the universe are the narrow jets that emanate from vicinity of powerful black holes in certain types of galactic nuclei. These narrow beams can stretch across millions of light-years, and they transport huge amounts of energy from the nuclear black hole regions into intergalactic space. The jets were discovered at radio wavelengths, but more recently have been found to emit at X-ray wavelengths as well. The X-ray emission is thought to be produced principally by one of two mechanisms that involve the highly energetic electrons in the jet: either their scattering of the light of the cosmic microwave background radiation (the CMBR - the remnant light of the big bang), or their radiating in the presence of strong magnetic fields. Each mechanism sheds light on the nature of the driving source(s) around the black hole, and the environment in which the jets develop. But so far many aspects of these X-ray jets remain controversial, leaving the nature of the most dramatic cosmic phenomenon very uncertain.

Two SAO astronomers, Dan Harris and Aneta Siemiginowska, together with eight of their colleagues, have used the Chandra X-ray Observatory to probe the X-ray emission from the million-light-year-long bipolar jet in the galaxy 3C353. They have, for the first time, been able to detect the X-ray emission all along the jet and its numerous knots of activity, as well as around the nucleus itself. In particular, they discover X-ray emission from the jet on both sides of the nucleus. Although the predominant view has been that X-ray emission in this object's jets arises from CMBR scattering, the new results strongly disagree with this model because it predicts that the scattering will only be seen from the jet on the near side. The data point instead to the importance of magnetic field effects. When compared with data at radio wavelengths, the results also imply that the several knots could have been ejected from the nucleus, and that the local, small-scale environment of the jet (not just the large-scale environment) is critically important. Although many mysteries remain, these new results have corrected a basic misunderstanding about these dramatic cosmic structures, at least in this one powerful galaxy.

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