## Abstract

We consider a two-parameter family of cylindrical force-free equilibria, modeled to match numerical simulations of relativistic force-free jets. We study the linear stability of these equilibria, assuming a rigid impenetrable wall at the outer cylindrical radius R_{j} . Equilibria in which the Lorentz factor γ(R) increases monotonically with increasing radius R are found to be stable. On the other hand, equilibria in which γ(R) reaches a maximum value at an intermediate radius and then declines to a smaller value γ_{j} at R_{j} are unstable. A feature of these unstable equilibria is that poloidal field line curvature plays a prominent role in maintaining transverse force balance. The most rapidly growing mode is an m = 1 kink instability which has a growth rate (0.4/γ_{j})(c/R _{j} ). The e-folding length of the equivalent convected instability is 2.5γ_{j} R_{j} . For a typical jet with an opening angle θ_{j} few/γ_{j}, the mode amplitude grows only weakly with increasing distance from the base of the jet. The growth is much slower than one might expect from a naive application of the Kruskal-Shafranov stability criterion.

Original language | English (US) |
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Pages (from-to) | 1681-1694 |

Number of pages | 14 |

Journal | Astrophysical Journal |

Volume | 697 |

Issue number | 2 |

DOIs | |

State | Published - 2009 |

## Keywords

- Galaxies: jets
- Instabilities
- MHD

## ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science