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Why Interstellar Ice Dust Grains Should Be Elongated

Bellan, P. M. (2020) Why Interstellar Ice Dust Grains Should Be Elongated. Astrophysical Journal, 905 (2). Art. No. 96. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20201218-123333435

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Abstract

Models of interstellar dust alignment assume that dust grains are elongated, but none of these models explain why dust grains should be elongated. On the other hand, models of interstellar dust grain growth assume that dust grains are spherical and not elongated. We show that when dusty plasma effects and the dipole moment of water molecules are together taken into account, ice grains in interstellar space should be prolate ellipsoids and not spheres. Dusty plasma analysis shows that an ice grain is charged to a negative potential that has magnitude nearly equal to that of the electron temperature. Several different mechanisms causing deviation from sphericity are identified; these mechanisms involve the interaction of the dipole moment of water molecules with electric fields associated with ice grain charging. These mechanisms include the focusing of water molecule trajectories, the migration of water molecules in a quasi-liquid layer on the grain surface toward regions where the electric field is strongest, the enhancement of this migration by the bombardment of energetic protons that gain energy upon falling into the ice grain negative potential, and mutual repulsion by electric charges having the same sign. The aspect ratio is established shortly after the ice grain is formed, and then is maintained as the grain grows.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/abc55bDOIArticle
https://iopscience.iop.org/article/10.3847/1538-4357/abc55bPublisherArticle
ORCID:
AuthorORCID
Bellan, P. M.0000-0002-0886-8782
Additional Information:© 2020 The American Astronomical Society. Received 2020 August 25; revised 2020 October 12; accepted 2020 October 26; published 2020 December 17. Supported by the National Science Foundation/Department of Energy Partnership in Basic Plasma Science and Engineering via USDOE Award DE-SC0020079.
Funders:
Funding AgencyGrant Number
NSFUNSPECIFIED
Department of Energy (DOE)DE-SC0020079
Subject Keywords:Very small grains ; Interstellar dust processes ; Laboratory astrophysics ; Interstellar magnetic fields ; Interstellar molecules ; Interstellar emissions ; Starlight polarization ; Water vapor ; Plasma astrophysics ; Ice formation
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Very small grains (1770); Interstellar dust processes (838); Laboratory astrophysics (2004); Interstellar magnetic fields (845); Interstellar molecules (849); Interstellar emissions (840); Starlight polarization
Record Number:CaltechAUTHORS:20201218-123333435
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201218-123333435
Official Citation:P. M. Bellan 2020 ApJ 905 96
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107203
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Dec 2020 21:09
Last Modified:18 Dec 2020 21:09

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