Laboratory Experiments on Rotation and Alignment of the Analogs of Interstellar Dust Grains by Radiation

Abstract

The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models, and numerical studies of grain rotation and alignment with respect to the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in grain rotation and alignment has not been achieved. As there appear to be no experimental data available on this subject, we have carried out some unique experiments to illuminate the processes involved in the rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron /submicron-sized, nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of $10 À3 to 10 À5 torr. The particles are illuminated by laser light at 5320 8, and the grain rotation rates are obtained by analyzing the low-frequency ($0-100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in light of the current theories of alignment.

Dusty Plasma Effects in Near Earth Space and Interplanetary Medium

“…For the dust species and interplanetary medium conditions considered Mukai and Schwehm find that the dust particles suffer only moderate erosion by sputtering before reaching the dust sublimation zone (see Section 5.2.5 related laboratory studies). Dust near the Sun can also be destroyed by rotational bursting (Misconi 1993, Abbas 2004). The dust PR effect varies and is enhanced during coronal mass ejections (Ragot and Kahler 2003).…”

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

“…In outer parts of the coma and in the tail, the alignment via radiative torques and interaction with solar wind could be important. For the comet environment the most important are mechanical alignment of grains rotating thermally (Gold, 1952;Purcell, 1979;Dolginov and Mytrophanov, 1976;Lazarian, 1994Lazarian, , 1997aLazarian, ,1997bRoberge et al, 1995) and suprathermally (Lazarian, 1995;Lazarian et al, 1996;Lazarian and Draine, 1997;Lazarian and Efroimsky, 1999) and radiative torque alignment (Dolginov, 1972;Dolginov and Mytrophanov, 1976;Weingartner, 1996, 1997;Weingartner and Draine, 2003;Abbas et al, 2004;Cho and Lazarian, 2005). For the review of the mechanisms of grain alignment see Lazarian ( 2003).…”

Simulations of polarized dust emission

“…Draine & Weingartner (1996) demonstrated the efficiency of radiative torques using numerical simulations, while Abbas et al (2004) demonstrated it in a laboratory setup. The radiative torque mechanism means the transfer of momentum by collisions of photons onto the grain, causing a torque which makes the grain rotate around its axis.…”