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Hybrid Simulations of Supersonic Shear Flows. I. Particle Acceleration

Year: 2026
Type: article
Abstract: Supersonic flows are ubiquitous in warm and cool media; their dissipation leads to heating, generation of nonthermal particles, and amplification of background magnetic fields. We present 2D hybrid (kinetic ions–fluid electrons) simulations of decaying shear flows across the subsonic-to-supersonic transition, finding that the canonical Kelvin–Helmholtz instability in subsonic cases gives way to the formation of shocklets in supersonic shears, where dissipation is faster and nonthermal particles are produced. We discuss the dependence on the flow Mach number of particle acceleration, the viscosity induced by kinetic effects, and the production of magnetic turbulence. We outline the potential impact of these findings for turbulence in the warm interstellar medium, for molecular clouds, and for accretion disks, leaving to a companion paper the discussion of the effects on the shear of self-generated and preexisting energetic particles.
DOI: 10.3847/1538-4357/ae4d45
Language: English
Open Access status: gold
Estimated APC paid: $4,499
Award: ONE OF THE MOST IMPORTANT SCIENTIFIC CONTRIBUTION OF THE FERMI SATELLITE HAS BEEN TO SHOW THAT THE GAMMA-RAY EMISSION FROM SEVERAL SUPERNOVA REMNANTS (SNRS) IS OF HADRONIC ORIGIN THEREBY SUPPORTING THE IDEA THAT SNRS ARE THE SOURCES OF GALACTIC COSMIC RAYS (CRS). ALMOST ALL GEV--BRIGHT SNRS EXPAND INTO PARTIALLY-NEUTRAL MEDIA AND/OR ARE ASSOCIATED WITH DENSE MOLECULAR CLOUDS (MCS). IN THE PRESENCE OF NEUTRAL HYDROGEN THE SHOCK DYNAMICS THE SPECTRUM OF ACCELERATED PARTICLES AND THE CR--MAGNETIC FIELD COUPLING ARE RADICALLY DIFFERENT THAN IN FULLY-IONIZED PLASMAS. HOWEVER THE EFFECTS OF NEUTRALS ARE USUALLY NEGLECTED IN CALCULATIONS OF CR ACCELERATION AND PROPAGATION. WE WILL USE SELF-CONSISTENT KINETIC SIMULATIONS OF COLLISIONLESS SHOCKS PROPAGATING IN PARTIALLY-IONIZED PLASMAS TO ASSESS THE IMPACT OF PHENOMENA SUCH AS CHARGE EXCHANGE IONIZATION AND ION--NEUTRAL DAMPING ON SHOCK DYNAMICS CR ACCELERATION AND MAGNETIC FIELD AMPLIFICATION WHICH ARE NEEDED TO CHARACTERIZE THE HADRONIC GAMMA-RAY EMISSION OBSERVED IN SNR/MC SYSTEMS.
OpenAlex ID: W7147306981
FWCI: 3.121
Cites: 76
Cited by: 1
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