J. A. Eilek, F. N. Owen

If our eyes were sensitive to radio waves or to X-rays, we would see a completely different sky. If we saw radio, we would see a sky dominated by quasars and radio galaxies. If we saw X-rays, we would see a sky dominated by clusters of galaxies (and some nearby stars and galactic nebulae). New developments in radio and X-ray astronomy allow us to study these fascinating objects. Radio galaxies, in often live in clusters of galaxies -- which are the largest gravitationally bound objects in the universe. In radio galaxies, a central black hole is believed to drive a jet of hot plasma out into the intergalactic atmosphere. The interaction of the jet with this atmosphere produces the radio galaxies we see. However, we are far from understanding how this works.

Our group has undertaken a program to gather VLA radio data and X-ray data from the ROSAT sattelite on a large number of these galaxies. Our goal is to understand he physics of these systems. We are attempint to apply a broad brush and also to study fine detail. That is, one needs to collect data on large numbers of radio galaxies, in order to determine trends: what does a young radio galaxy look like? What about an old one? How does their location in the cluster atmosphere affect them? In addition, one needs to study a few in great detail: what does the jet look like on small scales? On large? How does it connect back to the central black hole? How does it disturb the atmosphere around it? We are in the midst of doing both things: studying a few sources in detail, and analyzing a large data base of combined radio, optical and X-ray data.

In addition to data, there must be interpretation: what is the underlying physics? We know that the radio emission comes from a magnetized, relativistic plasma: it may be electron-proton, or it may be electron-positron. However, we do not know for certain how this plasma is created, how it is driven out from the black hole in the galactic core, or how it interacts with the cluster atmosphere to form the radio structures that we see. There are many local examples of such plasmas in laboratory fusion devices, and also in the earth's magnetosphere and solar wind which can be directly probed with sattelites. In a theoretical program which complements our data acquisiton and analysis work, we are attempting to use knowledge gained from local plasmas, to understand the dynamics and evolution of these distant radio galaxies.