Fast Dissipation of Colliding Alfvén Waves in a Magnetically Dominated Plasma

Journal Article · 30 June 2021 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/abfe5f · OSTI ID:1853745

Li, Xinyu  ^[1]; Beloborodov, Andrei M. ^[2]; Sironi, Lorenzo  ^[3]

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1. Canadian Institute for Theoretical Astrophysics (Canada); Perimeter Institute for Theoretical Physics (Canada).; OSTI
2. Columbia Univ., New York, NY (United States). Department of Physics and Columbia Astrophysics Laboratory; Max Planck Institute for Astrophysics (Germany)
3. Columbia Univ., New York, NY (United States). Department of Astronomy and Columbia Astrophysics Laboratory

Magnetic energy around compact objects often dominates over plasma rest mass, and its dissipation can power the object's luminosity. We describe a dissipation mechanism that works faster than magnetic reconnection. The mechanism involves two strong Alfvén waves with anti-aligned magnetic fields B₁ and B₂ that propagate in opposite directions along the background magnetic field B₀ and collide. The collision forms a thin current sheet perpendicular to B₀, which absorbs the incoming waves. The current sheet is sustained by an electric field E breaking the magnetohydrodynamic condition E < B and accelerating particles to high energies. We demonstrate this mechanism with kinetic plasma simulations using a simple setup of two symmetric plane waves with amplitude A = B₁/ B₀ = B₂/B₀ propagating in a uniform B₀. The mechanism is activated when A > 1/2. It dissipates a large fraction of the wave energy, † = (2A - 1)/A², reaching 100% when A = 1. The plane geometry allows one to see the dissipation process in a one-dimensional simulation. We also perform two-dimensional simulations, enabling spontaneous breaking of the plane symmetry by the tearing instability of the current sheet. At moderate A of main interest, the tearing instability is suppressed. Dissipation transitions to normal, slower, magnetic reconnection at A $$\gg$$ 1. The fast dissipation described in this paper may occur in various objects with perturbed magnetic fields, including magnetars, jets from accreting black holes, and pulsar wind nebulae.

• Research Organization: Columbia Univ., New York, NY (United States); Columbia University, New York, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: SC0021254
• OSTI ID: 1853745
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 915; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English