On the dissipation of the rotation energy of dust grains in interstellar magnetic fields

doi:10.1093/MNRAS/STW020

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On the dissipation of the rotation energy of dust grains in interstellar magnetic fields

Journal Article•DOI•

On the dissipation of the rotation energy of dust grains in interstellar magnetic fields

01 Apr 2016-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 457, Iss: 2, pp 1626-1635

TL;DR: In this paper, a new mechanism is described, analyzed and visualized for the dissipation of suprathermal rotation energy of molecules in magnetic fields, a necessary condition for their alignment.

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Abstract: A new mechanism is described, analyzed and visualized, for the dissipation of suprathermal rotation energy of molecules in magnetic fields, a necessary condition for their alignment. It relies upon the Lorentz force perturbing the motion of every atom of the structure, as each is known to carry its own net electric charge because of spatial fluctuations in electron density. If the molecule is large enough that the frequency of its lowest-frequency phonon lies near or below the rotation frequency, then the rotation couples with the molecular normal modes and energy flows from the former to the latter. The rate of this exchange is very fast, and the vibrational energy is radiated away in the IR at a still faster rate, which completes the removal of rotation energy. The energy decay rate scales like the field intensity, the initial angular velocity, the number of atoms in the grain and the inverse of the moment of inertia. It does not depend on the susceptibility. Here, the focus is on carbon-rich molecules which are diamagnetic. The same process must occur if the molecule is paramagnetic or bathes in an electric field instead. A semi-empirical method of chemical modeling was used extensively to illustrate and quantify these concepts as applied to a hydrocarbon molecule. The motion of a rotating molecule in a field was monitored in time so as to reveal the energy transfer and visualize the evolution of its orientation towards the stable configuration.

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Journal Article•DOI•

Quantum Suppression of Alignment in Ultrasmall Grains: Microwave Emission from Spinning Dust will be Negligibly Polarized

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B. T. Draine¹, Brandon S. Hensley²•Institutions (2)

Princeton University¹, California Institute of Technology²

27 Oct 2016-The Astrophysical Journal

TL;DR: In this article, the quantization of energy levels in very nanoparticles suppresses dissipative processes that convert grain rotational kinetic energy into heat, and the suppression of dissipation can be extreme.

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Abstract: The quantization of energy levels in very nanoparticles suppresses dissipative processes that convert grain rotational kinetic energy into heat. For grains small enough to have GHz rotation rates, the suppression of dissipation can be extreme. As a result, alignment of such grains is suppressed. This applies both to alignment of the grain body with its angular momentum J, and to alignment of J with the local magnetic field B_0. If the anomalous microwave emission is rotational emission from spinning grains, it will be negligibly polarized at GHz frequencies, with P < 10^{-6} at frequencies above 10 GHz.

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35 citations

Cites background from "On the dissipation of the rotation ..."

...Papoular (2016) recently proposed that interstellar grains can be aligned with the magnetic field B0 even if the grain material has zero magnetic susceptibility, because the ions and electrons in the grain will experience time-varying Lorentz forces unless the grain angular velocity ω ‖ B0....
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Journal Article•DOI•

Quantum Suppression of Alignment in Ultrasmall Grains: Microwave Emission from Spinning Dust will be Negligibly Polarized

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B. T. Draine¹, Brandon S. Hensley²•Institutions (2)

Princeton University¹, Jet Propulsion Laboratory²

21 May 2016-arXiv: Astrophysics of Galaxies

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32 citations

Journal Article•DOI•

Detection of Polarized Infrared Emission by Polycyclic Aromatic Hydrocarbons in the MWC 1080 Nebula

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Han Zhang¹, Charles M. Telesco¹, Thiem Hoang², Aigen Li³, Eric Pantin⁴, Eric Pantin¹, Christopher M. Wright⁵, Dan Li⁶, Peter J. Barnes¹, Peter J. Barnes⁷ - Show less +6 more•Institutions (7)

University of Florida¹, Korea Astronomy and Space Science Institute², University of Missouri³, Paris Diderot University⁴, University of New South Wales⁵, University of Pennsylvania⁶, University of New England (Australia)⁷

17 Jul 2017-The Astrophysical Journal

TL;DR: In this article, the authors reported the definite detection of polarized polycyclic aromatic hydrocarbons (PAHs) emission at 11.3 $\mu$m in the nebula associated with the Herbig be star MWC 1080.

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Abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in astrophysical environments, as revealed by their pronounced emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 $\mu$m commonly ascribed to the C--H and C--C vibrational modes. Although these features have long been predicted to be polarized, previous searches for PAH polarization led to null or, at best, tentative detections. Here we report the definite detection of polarized PAH emission at 11.3 $\mu$m in the nebula associated with the Herbig Be star MWC 1080. We measure a polarization degree of 1.9$\pm$0.2\%, which is unexpectedly high compared to models. This poses a challenge in the current understanding of the alignment of PAHs, which is required to polarize the PAH emission but thought to be substantially suppressed. PAH alignment with a magnetic field via a resonance paramagnetic relaxation process may account for such a high level of polarization.

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12 citations

Cites background from "On the dissipation of the rotation ..."

...…it seems that other physical processes such as Faraday rotation braking that facilitate the alignment of nanoparticles need to be considered (Papoular 2016), since it is evident that the starlight anisotropy scheme alone in L88 is not sufficient to explain the measured high level of…...
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Journal Article•DOI•

Effect of Alignment on Polarized Infrared Emission from Polycyclic Aromatic Hydrocarbons

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Thiem Hoang¹•Institutions (1)

Korea Astronomy and Space Science Institute¹

31 Mar 2017-The Astrophysical Journal

TL;DR: In this article, the effect of polycyclic aromatic hydrocarbons (PAHs) alignment with the magnetic field has been studied and a new model of polarized PAH emission has been proposed to test the alignment physics of ultrasmall grains.

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Abstract: Polarized emission from polycyclic aromatic hydrocarbons (PAHs) potentially provides a new way to test the basic physics of the alignment of ultrasmall grains. In this paper, we present a new model of polarized PAH emission that takes into account the effect of PAH alignment with the magnetic field. We first generate a large sample of the grain angular momentum by simulating the alignment of PAHs due to resonance paramagnetic relaxation that accounts for various interaction processes. We then calculate the polarization level of the PAH emission features for the different phases of the interstellar medium, including the cold neutral medium (CNM), reflection nebulae (RNe), and photodissociation regions. We find that a moderate degree of PAH alignment can significantly enhance the polarization degree of the PAH emission compared to the previous results obtained with randomly oriented angular momentum. In particular, we find that the smallest negatively charged PAHs in RNe can be excited to slightly suprathermal rotation due to enhanced ion collisional excitation, resulting in an increase of the polarization with the ionization fraction. Our results suggest that an RN is the most favorable environment in which to observe polarized PAH emission and to test the alignment physics of nanoparticles. Finally, we present an explicit relationship between the polarization level of PAH emission and the degree of external alignment for the CNM and RNe. The obtained relationship will be particularly useful for testing the alignment physics of PAHs in future observations.

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7 citations

Cites background from "On the dissipation of the rotation ..."

...Meanwhile, Papoular (2016) suggested that Faraday rotation braking may enhance alignment of diamagnetic molecules (e.g., PAHs) due to direct transfer of rotational energy into heat via molecular vibrations....
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...Meanwhile, Papoular (2016) suggested that Faraday rotation braking can facilitate the dissipation of rotational energy of diamagnetic grains that enhances internal alignment....
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Journal Article•DOI•

Candidate magnetic dust structures for star light polarization

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R. Papoular

21 Nov 2017-Monthly Notices of the Royal Astronomical Society

TL;DR: In this paper, the authors derived an expression for the damping time of the rotation of a particle in a magnetic field, under the Faraday braking torque, provided its electrical properties are known.

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Abstract: Rotation damping and alignment are discussed as prerequisites for polarization power. An expression is derived from first principles, for the damping time of the rotation of a particle in a magnetic field, under the Faraday braking torque, provided its electrical properties are known. This makes it possible to describe mathematically, in great detail, the motion of the particle and determine its ultimate state of motion, if a steady state is possible at all. This work defines, first, the necessary condition for the Faraday braking to be effective: a) the net electronic charge distribution should not be uniform throughout; b) the number of vibration modes should exceed a few tens. Resonance of rotation frequency with any of these modes is not a requirement. For alignment to be possible, the ratio of gyroscopic and conservative magnetic to non-conservative (retarding) magnetic torques must be low. Either dia-, para- or ferro-magnetism can do, and a small susceptibility is enough and even preferable. This opens up a wide spectrum of possible candidates. A few examples are given.

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3 citations

Cites background or methods from "On the dissipation of the rotation ..."

...Papoular (2016) offered a grossly approximate expression for τb, featuring the dipole moment, D, and the radius of gyration, RG, corresponding to the rotation axis of interest....
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...A much more accurate expression can be obtained as follows, using the capabilities of the same Hyperchem chemical modeling package, available from Hypercube Inc., publication HC50-00-02-00; for details, see Papoular (2016)....
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...…model have recently demonstrated the existence of a rotation braking torque associated with the Faraday force, q~V × ~B, acting upon the positive and negative partial (Mulliken) atomic charges of any electrically neutral diamagnetic dust paricle carrying an electric dipole moment (Papoular 2016) ....
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...Assume the molar susceptibilities to be the same as those measured for the trioS molecule (Papoular 2016): V χ1,2,3 = −2.3,−2.39,−2 10−29 cm3 (Gauss system), which are close to those of graphite....
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...As in Papoular (2016), assume therefore, as a mathematical approximation, that, for each vibrating charge, the number of superimposed normal modes is so large that the vector sum of all corresponding velocities averages out, leaving only the local angular velocity....
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References

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Abstract: 3rd edition, complete modern revision C. Kittel London: John Wiley. 1966. Pp. 648. Price £4 14s. Kind's new edition is to be welcomed. There is a revised format and attractive illustrations, and with the inclusion of much new material this book has become one of the best sources for undergraduate teaching. It is above all an interesting book, likely to give the student a wish to dig deeper into the solid state.

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TL;DR: In this paper, the authors present an overview of the physical properties of Grains and their properties in terms of elastic collisions, grain alignment, and overall equilibrium in a stellar environment.

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Abstract: Interstellar Matter-- An Overview. Elastic Collisions and Kinetic Equilibrium. Radiative Processes. Excitation. Ionization and Dissociation. Kinetic Temperature. Optical Properties of Grains. Polarization and Grain Alignment. Physical Properties of Grains. Dynamical Principles. Overall Equilibrium. Explosive Motions. Gravitational Motion. Symbols. Index.

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2,462 citations

"On the dissipation of the rotation ..." refers background or methods in this paper

...A number of interpretations of this phenomenon were offered (see, for instance, reviews and bibliography by Spitzer 1978, Hildebrand 1988, Roberge 2004, Lazarian and Cho 2005 and Lazarian 2007)....
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...The resulting angular velocity, ω, is generally taken to be as high as 109 s−1 (see Spitzer 1978 ) for grain sizes of 10−5 cm....
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...This paradigm has been elaborated on (see Jones and Spitzer 1967 and Spitzer 1978, Purcell 1969 and 1979, for instance) and several variants were later proposed, especially in relation to the observed so-called anomalous microwave emission (AME), in particular those involving rapidly spinning ultra…...
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