Letter to the Editor

Dust-driven streaming instability and magnetic field amplification downstream of supernova remnant shocks

¹ Université de Paris Cité, CNRS, Astroparticule et Cosmologie, F-75006 Paris, France
² Center for Astrophysics, 60 Garden St., Cambridge, MA 02176, USA
³ LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 92190 Meudon, France
⁴ Istituto Nazionale di Astrofisica – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁵ (IFJ-PAN) Institute of Nuclear Physics Polish Academy of Sciences, PL-31342 Krakow, Poland
⁶ Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 9 April 2026
Accepted: 26 June 2026

Abstract

Context. The acceleration of cosmic rays up to PeV energies at supernova remnant shocks requires an amplification of the ambient magnetic field. The amplification mechanism must operate upstream of the shock, to prevent the escape of particles from the system. Observational evidence of field amplification has indeed been obtained by means of X-ray observations. However, such observations only constrain the magnetic field strength downstream of the shock.

Aims. Here we describe a mechanism of magnetic field amplification that operates downstream of the shock. It is based on a plasma instability triggered by the drift of charged interstellar dust grains overtaken by the shock.

Methods. We computed the growth rate of the instability, we estimated the level of magnetic field amplification expected downstream of supernova remnant shocks, and we compared our results with observations.

Results. In some cases (most notably Cas A) this mechanism might explain the presence of the X-ray filaments observed at supernova remnant shocks, without requiring any amplification of the magnetic field upstream of the shock and therefore any acceleration of cosmic rays to ultrahigh energies.