Hysteresis of Backflow Imprinted in Collimated Jets

TL;DR

This study uses relativistic hydrodynamical simulations to explore two types of backflow in jets, revealing how backflow behavior influences jet structure and velocity, with implications for observing young jets.

Contribution

It identifies and characterizes two distinct backflow types in relativistic jets and explains their impact on jet morphology and dynamics, a novel insight into jet backflow behavior.

Findings

Quasi-straight backflow occurs at high head speeds.

Bent backflow causes jet broadening and velocity decrease.

Backflow imprinting leads to node and anti-node structures.

Abstract

We report two different types of backflow from jets by performing 2D special relativistic hydrodynamical simulations. One is anti-parallel and quasi-straight to the main jet (quasi-straight backflow), and the other is bent path of the backflow (bent backflow). We find that the former appears when the head advance speed is comparable to or higher than the local sound speed at the hotspot while the latter appears when the head advance speed is slower than the sound speed bat the hotspot. Bent backflow collides with the unshocked jet and laterally squeezes the jet. At the same time, a pair of new oblique shocks are formed at the tip of the jet and new bent fast backflows are generated via these oblique shocks. The hysteresis of backflow collisions is thus imprinted in the jet as a node and anti-node structure. This process also promotes broadening of the jet cross sectional area and it also causes a decrease in the head advance velocity. This hydrodynamic process may be tested by observations of compact young jets.