A Magnetohydrodynamic Model of the M87 Jet I: Superluminal Knot Ejections from HST-1 as Trails of Quad Relativistic MHD Shocks

TL;DR

This paper introduces a new MHD-based model for the M87 jet, explaining superluminal knot ejections as quad relativistic MHD shocks within a magnetically dominated, helical jet structure, supported by numerical simulations.

Contribution

It proposes a novel paradigm where superluminal knots are quad relativistic MHD shocks, integrating new shock wave concepts into astrophysical jet modeling.

Findings

Superluminal knots are modeled as quad relativistic MHD shocks.

Numerical simulations support the shock-based ejection mechanism.

The model explains jet substructures on large scales.

Abstract

This is the first in a series of papers that introduces a new paradigm for understanding the jet in M87: a collimated relativistic flow in which strong magnetic fields play a dominant dynamical role. Here wefocus on the flow downstream of HST-1 - an essentially stationary flaring feature that ejects trails of superluminal components. We propose that these components are quad relativistic magnetohydrodynamic shock fronts (forward/reverse fast and slow modes) in a narrow jet with a helically twisted magnetic structure. And we demonstrate the properties of such shocks with simple one-dimensional numerical simulations. Quasi-periodic ejections of similar component trails may be responsible for the M87 jet substructures observed further downstream on 100 - 1,000 pc scales. This new paradigm requires the assimilation of some new concepts into the astrophysical jet community, particularly the behavior of slow/fast-mode waves/shocks and of current-driven helical kink instabilities. However, the prospects of these ideas applying to a large number of other jet systems may make this worth the effort.