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Session 45 - The Structure and Evolution of The Universe - II.
Topical, Oral session, Tuesday, June 09
Presidio,
Cosmic jets are among the most spectacular dynamical phenomena in the universe. Although jets can be found emanating from the cores of quasars and other active galactic nuclei, compact binary star systems in our Galaxy, and even regions of star formation, we do not yet understand fully how nature creates such high-energy, high-speed flows that are so well focused. Current models involving magnetized winds accelerating along the rotational poles of disks of hot gas falling toward a black hole, neutron star, or star are difficult to test because the site where most of the "action" occurs cannot be resolved by current instruments.
I will present images and other observations of cosmic jets that illustrate our current state of both knowledge and ignorance about these fascinating structures. I will then focus on the major outstanding theoretical issues: How does a system in which most of the matter is falling inward generate an energetic outflow in the form of well-focused jets? How is the material in the jet energized at the base of the jet and re-energized downstream from time to time? How are flow speeds of up to - and perhaps exceeding - 99.9% the speed of light attained in the jets? How are individual particles accelerated to such high energies that they emit very-high energy gamma-rays? What causes the rapid changes in brightness that seem to indicate extraordinarily high energy densities of both photons and particles?
I will discuss the prospects of answering these questions within the next ten years through observations with current and future NASA missions coupled with ground-based instruments. For example, SIRTF will explore with unprecedented sensitivity the spectral region (infrared) where most of the luminosity of the direct radiation from jets is emitted, while GLAST and ground-based Cherenkov detectors such as VERITAS will measure the bulk of the scattered emission. AXAF and XMM will explore the X-ray emitting regions with unprecedented spatial and spectral resolution, while a mm-wave space VLBI mission currently in the concept phase would provide images of jets closer to the ultimate energy source than has been possible previously. These, combined with advances in computational theoretical astrophysics, should answer the above questions and, as usual, raise new ones.
