Highlights of Extragalactic & Jet Research

1. How do Radio Galaxies form?
In the late 1970s, jets were discovered in megaparsec-long radio galaxies. I developed a 'slender' hydrodynamical theory for jets. This involved the first quantitative analysis of jet warping, bending and disruption in galactic halos. I established a background of theory to which observed behaviour is compared and contrasted. A full treatment of laminar jets, including the nozzle, gravity and splitting, has since been completed.

2. What are Hot Spots?
Hot spots are created where a jet finally crashes into the surrounding medium. I made the first sophisticated numerical simulations of supersonic jets with Michael Norman and Larry Smarr (Illinois)$^7$. Cocoons, oblique shocks and Mach discs were revealed. Synthetic 'hot spot' maps were generated which contain many of the observed hot spot features and led to the first classification scheme.

3. How do Jets form?
Stellar and extragalactic outflows may be funnelled through de Laval nozzles$^4$, regions which are prone to Rayleigh-Taylor and Kelvin-Helmholtz fluid instabilities. I extended the so-called Twin Exhaust Model, using numerical simulations to show that hot gas can be ejected in three forms: jets, bubbles and clouds. The properties of black holes were then constrained.

4. How do Galactic Nuclei and Quasars interact with their environments?
I produced the 'Catapult' model for the extended regions of Active Galactic Nuclei and the 'Candle Flame' model for the focussing of Stellar Winds into bipolar outflows via accretion disks. Active Galactic Nuclei were further explored in the mid 80s. The interaction of a central 'monster' with its environment is through a number of supply and escape routes. This was discussed in the 'Duelling Wind' and 'Floppy Disc'. Here a wind from a black hole collides into an X-ray heated wind from a surrounding disc. Predictions for the core of a quasar were then presented. The model is appropriate for the class of 'Broad Absorption Line' quasars which possess the signature of a disk-shaped outflow.

5. Are Protostellar Outflows driven by Jets?
I have confirmed that Molecular Jets do indeed generate the structures observed around protostars. A hydrocode to follow the molecular-atomic transitions of hydrogen was developed with Suttner and Yorke (Wuerzburg). The simulated images and spectroscopy from infrared and submullimetre lines solve a number of problems and make clear predictions for the classical Bipolar Outflows.

6. What do Jets reveal about Protostars?
What Jet Structure arises when a pulsating energy source drives a supersonic flow. The pulsation model has been examined for identifying features with Suttner (Wuerzburg) and Zinnecker (Potsdam). Sawtooth velocity structures were found to develop intermediate teeth. These teeth possess high velocity gradients, providing a motivation for high-resolution observations. The hypotheses that the pulses are hammer-like and that the jet is sheared are being tested in the 'Hammer Jet' model.

Last Revised: 2010 June 30th