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Ubiquitous instabilities of dust moving in magnetized gas

Hopkins, Philip F. and Squire, Jonathan (2018) Ubiquitous instabilities of dust moving in magnetized gas. Monthly Notices of the Royal Astronomical Society, 479 (4). pp. 4681-4719. ISSN 0035-8711.

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Squire & Hopkins showed that coupled dust–gas mixtures are generically subject to ‘resonant drag instabilities’ (RDIs), which drive violently growing fluctuations in both. But the role of magnetic fields and charged dust has not yet been studied. We therefore explore the RDI in gas that obeys ideal MHD and is coupled to dust via both Lorentz forces and drag, with an external acceleration (e.g. gravity, radiation) driving dust drift through gas. We show this is always unstable, at all wavelengths and non-zero values of dust-to-gas ratio, drift velocity, dust charge, ‘stopping time’ or drag coefficient (for any drag law), or field strength; moreover, growth rates depend only weakly (sub-linearly) on these parameters. Dust charge and magnetic fields do not suppress instabilities, but give rise to a large number of new instability ‘families,’ each with distinct behavior. The ‘MHD-wave’ (magnetosonic or Alfvén) RDIs exhibit maximal growth along ‘resonant’ angles where the modes have a phase velocity matching the corresponding MHD wave, and growth rates increase without limit with wavenumber. The ‘gyro’ RDIs are driven by resonances between drift and Larmor frequencies, giving growth rates sharply peaked at specific wavelengths. Other instabilities include ‘acoustic’ and ‘pressure-free’ modes (previously studied), and a family akin to cosmic ray instabilities that appear when Lorentz forces are strong and dust streams super-Alfvénically along field lines. We discuss astrophysical applications in the warm ISM, circum-galactic medium/inter-galactic medium (CGM/IGM), H II regions, SNe ejecta/remnants, Solar corona, cool-star winds, GMCs, and AGN.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Squire, Jonathan0000-0001-8479-962X
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 June 5. Received 2018 June 4; in original form 2018 January 27. Published: 18 June 2018. We would like to thank E. S. Phinney and E. Quataert for helpful discussions, as well as our anonymous referee. Support for PFH & JS was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. JS was funded in part by the Gordon and Betty Moore Foundation through Grant GBMF5076 to Lars Bildsten, Eliot Quataert, and E. Sterl Phinney.
Group:TAPIR, Astronomy Department
Funding AgencyGrant Number
Alfred P. Sloan FoundationUNSPECIFIED
Gordon and Betty Moore FoundationGBMF5076
Subject Keywords:accretion, accretion discs – instabilities – turbulence – planets and satellites: formation – ISM: kinematics and dynamics – galaxies: formation
Issue or Number:4
Record Number:CaltechAUTHORS:20180829-160558722
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Official Citation:Philip F Hopkins, Jonathan Squire; Ubiquitous instabilities of dust moving in magnetized gas, Monthly Notices of the Royal Astronomical Society, Volume 479, Issue 4, 1 October 2018, Pages 4681–4719,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89291
Deposited By: Tony Diaz
Deposited On:29 Aug 2018 23:20
Last Modified:09 Mar 2020 13:19

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