Description of Project Problem

Over the last decade the quantity and quality of images of extragalactic relativistic jets have increased to a point where it has become evident that curvature of light-year-scale flows is the norm, not the exception (e.g., Wardle et al. 1994). Some of this curvature may be `apparent', resulting from a more modestly curved flow seen close to the line of sight. Nevertheless, such flows must posses some intrinsic curvature, and thus their 3-D morphology must be addressed. This raises both questions and possibilities: how can highly relativistic flows suffer significant curvature, and yet retain their integrity? It has been argued (Begelman, Blandford & Rees 1984) that sublight-year-scale flows are highly dissipative, and should radiate a significant fraction of their flow energy if subjected to a perturbation such as bending. How do transverse shocks propagate along a curved flow? Will the shock plane rotate with respect to the flow axis; will the shock strengthen or weaken? What role does flow curvature have to play in explaining phenomena such as stationary knots between which superluminal components propagate (Shaffer et al. 1987), knots which brighten after an initial fading (Mutel et al. 1990), and changing component speed (Lobanov & Zensus 1996). Numerous lines of evidence point convincingly to the occurrence of oblique shocks (e.g., Heinz & Begelman 1997; Lister & Marscher 1999; Marscher et al. 1997; Polatidis & Wilkinson 1998); how do they form and evolve? All these issues are amenable to study through hydrodynamic simulation -- but all demand that such simulations be 3-D. Furthermore, it has become evident over the last five years that such highly energetic flows are also found in Galactic objects with stellar mass `engines'. In the galactic superluminals GRS~1915+105 (Mirabel & Rodríguez 1994, 1995) and GRO~J1655--40 (Hjellming & Rupen 1995; Tingay et al. 1995) the observed motions indicate jet flow speeds up to 92c. There is compelling evidence from the observation of optical afterglow that gamma-ray bursts are of cosmological origin, and whether produced by the mergers of compact objects, or accretion induced collapse (AIC), simple relativistic fireball models seem ruled out, the data strongly favoring highly relativistic jets (Dar 1998). Thus a detailed understanding of the dynamics of collimated relativistic flows has wide application in astrophysics. This grant application requests resources to perform an initial exploration of the key issues pertaining to the uniquely 3D dynamics of relativistic astrophysical flows.