Instabilities and the remarkable survivability of AGN jets.

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• Serguei Komissarov (Leeds)
• Monday 24 February 2025, 14:00-15:00
• MR14 DAMTP and online.

If you have a question about this talk, please contact Thomas Jannaud.

Jets powered by active galactic nuclei (AGN) appear impressively stable in comparison to their terrestrial and laboratory counterparts – they can be traced from their origin to distances exceeding their injection radius by up to a billion times. However some of them, the Fanaroff-Riley class I (FR-I) jets in particular, get disrupted and lose their coherence on the scale of host galaxy. It has been suggested that the survivability of AGN jets is related to their rapid expansion, and that the instabilities develop only when they eventually become confined/recollimated by the surrounding plasma.

Motivated by this hypothesis, we carried out 3D computer simulations of jets propagating through plasma with rapidly declining pressure and jets recollimated by galactic coronas with flat pressure distribution. The results support the stabilising role of jet expansion and show that the recollimation of unmagnetized jets by external pressure is indeed accompanied by a rapid development of instability and transition to a turbulent state. This instability is driven by the inertial force associated with the curved streamlines of recollimated jets and hence relates to the well-known centrifugal instability. Simulations of magnetised jets show that even relatively weak azimuthal magnetic field can suppress the recollimation instability, with the critical relativistic magnetisation parameter sigma about 0.01. These results are consistent with our heuristic analysis of the relativistic centrifugal instability (CFI) and the computer simulations of relativistic rotating fluids.

This talk is part of the DAMTP Astrophysics Seminars series.

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