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The dynamics of charged dust in magnetized molecular clouds

Lee, Hyunseok and Hopkins, Philip F. and Squire, Jonathan (2017) The dynamics of charged dust in magnetized molecular clouds. Monthly Notices of the Royal Astronomical Society, 469 (3). pp. 3532-3540. ISSN 0035-8711. doi:10.1093/mnras/stx1097.

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We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee directly simulated the dynamics of neutral dust grains in supersonic magnetohydrodynamic turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ∼1000 on small scales, with important implications for star formation, stellar abundances and dust behaviour and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small-charged grains (sizes ≪ 0.1 μm), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes ≳ 1 μm), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust–gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Squire, Jonathan0000-0001-8479-962X
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 May 4. Received 2017 April 9; in original form 2016 December 15. Published: 06 May 2017. We thank the anonymous referee and Matthew Goodson for a number of useful comments and suggestions. Support for HL & PFH was provided by NASA ATP Grant NNX14AH35G & 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. Numerical calculations were run on Caltech cluster ‘Zwicky’ (NSF MRI award #PHY-0960291) & XSEDE allocation TG-AST130039 supported by the NSF.
Group:TAPIR, Walter Burke Institute for Theoretical Physics, Astronomy Department
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
Subject Keywords:accretion, accretion discs – instabilities – turbulence – planets and satellites: formation – stars: formation – galaxies: formation – cosmology: theory
Issue or Number:3
Record Number:CaltechAUTHORS:20170828-090207603
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Official Citation:Hyunseok Lee, Philip F. Hopkins, Jonathan Squire; The dynamics of charged dust in magnetized molecular clouds, Monthly Notices of the Royal Astronomical Society, Volume 469, Issue 3, 11 August 2017, Pages 3532–3540,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80835
Deposited By: Tony Diaz
Deposited On:28 Aug 2017 19:01
Last Modified:15 Nov 2021 19:39

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