arXiv subjects

Chi-Hang Ng

Publications and source records attributed to Chi-Hang Ng.

2 recordsLinked to original sources

arXiv2025

Investigating the influence of the radiative torque disruption on the size evolution of dust in the heliosphere

In this paper, we conduct a detailed study on the effect of Radiative Torque Disruption (RATD) mechanism on the fragmentation of micrometer-sized dust grains into nanoparticles within the heliosphere. We start by estimating the disruption timescales for dust grains under various centrifugal stresses. Our numerical calculations demonstrate that RATD is a highly effective mechanism for breaking down micrometer-sized grains, producing nanoparticles more efficiently than other fragmentation processes. RATD also prevents micrometer-sized grains from being expelled by radiation pressure. Our findings indicate that the location of the present water snow line depends not only on temperature but also on the size of dust grains. For smaller grains, the snow line can shift outward beyond the position defined by thermal sublimation. Furthermore, we model the size distribution of dust grains modified by the RATD mechanism using a simplified model, showing that rotational disruption significantly decreases the number density of micrometer-sized grains while substantially increasing the number density of sub-micrometer-sized grains. However, the fraction of dust grains aligned at high-$J$ attractors by radiative torques less than 80\% can considerably weaken the effect of RATD on the grain size distribution. Finally, we suggest several experiments that could potentially test the RATD mechanism and discuss the uncertainties of our model in more realistic applications to heliospheric dust.

astro-ph.EP↗

arXiv2021

Effect of Dust Rotational Disruption by Radiative Torques and Implications for F-corona decrease revealed by the Parker Solar Probe

The first-year results from the Parker Solar Probe (PSP) reveal a gradual decrease of F-coronal dust from distances of $D=0.166-0.336$ AU (or the inner elongations of $\sim 9.22- 18.69~R_{\odot}$) to the Sun (Howard et al. 2019). Such a F-corona decrease cannot be explained by the dust sublimation scenario of the popular silicate composition that implies a dust-free-zone of boundary at heliocentric radius $R\lesssim 4-5R_{\odot}$, but may be explained by appealing to various dust compositions with different sublimation fronts. In this paper, we present an additional explanation for the F-corona decrease using our newly introduced mechanism of dust destruction so-called Radiative Torque Disruption (RATD) mechanism. We demonstrate that RATD rapidly breaks large grains into nanoparticles so that they can be efficiently destroyed by nonthermal sputtering induced by bombardment of energetic protons from slow solar winds, which extends the dust-free-zone established by thermal sublimation to $R_{dfz}\sim 8R_{\odot}$. Beyond this extended dust-free-zone, we find that the dust mass decreases gradually from $R\sim 42R_{\odot}$ toward the Sun due to partial removal of nanodust by nonthermal sputtering. The joint effect of RATD and nonthermal sputtering can successfully reproduce the gradual decrease of the F-corona between $19-9R_{\odot}$ observed by the PSP. Finally, the RATD mechanism can efficiently produce nanoparticles usually observed in the inner solar system.

astro-ph.SR↗