The Experts below are selected from a list of 3987 Experts worldwide ranked by ideXlab platform

Hoang Thiem - One of the best experts on this subject based on the ideXlab platform.

  • Rotational disruption of dust grains by mechanical torques for high-velocity gas-grain collisions
    'American Astronomical Society', 2020
    Co-Authors: Hoang Thiem, Lee Hyeseung
    Abstract:

    Dust grains moving at hypersonic velocities of $v_{d}\gtrsim 100\rm km~s^{-1}$ through an ambient gas are known to be destroyed by nonthermal sputtering. Yet, previous studies of nonthermal sputtering disregarded the fact that dust grains can be spun-up to suprathermal rotation by stochastic mechanical torques from gas-grain collisions. In this paper, we show that such grain suprathermal rotation can disrupt a small grain into small fragments because induced Centrifugal Stress exceeds the maximum tensile strength of grain material, $S_{\rm max}$. We term this mechanism {\it MEchanical Torque Disruption} (METD). We find that METD is more efficient than nonthermal sputtering in destroying smallest grains ($a

  • Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL
    2020
    Co-Authors: Tram, Le Ngoc, Hoang Thiem, Lee Hyeseung, Michail, Joseph M., Chuss, David T., Nickerson Sarah, Rangwala Naseem, Reach, William T.
    Abstract:

    Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of $T_{\rm d}\gtrsim 100\,\rm K$. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to Centrifugal Stress induced by radiative torques (RATs) is proposed by Hoang & Tram 2020 that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of three representative COMs which have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for $T_{\rm d}\gtrsim 71\,\rm K$. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.Comment: 13 pages, 9 figures, 1 table, accepted to Ap

  • Rotational Desorption of Ice Mantles and Complex Molecules from Suprathermally Rotating Dust Grains around Young Stellar Objects
    'American Astronomical Society', 2020
    Co-Authors: Hoang Thiem, Tram, Le Ngoc
    Abstract:

    Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from $T_{d}\sim 10\rm K$ to $\gtrsim 100$ K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects (YSOs) on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by Centrifugal Stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius $a \lesssim 10$\AA~ exhibit transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain or the same rate but with temperatures of $\sim 20-40$ K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to $T_{\rm gas}\sim 40\rm K$ and $n_{\rm H}\sim 10^{4}\rm cm^{-3}$. We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via rotational disruption mechanism, followed by rotational desorption of ice mantles.Comment: 17 pages, 11 figures; accepted to Ap

  • Dust Rotational Dynamics in C-shocks: Rotational Disruption of Nanoparticles by Stochastic Mechanical Torques and Spinning Dust Emission
    'American Astronomical Society', 2019
    Co-Authors: Hoang Thiem, Tram, Le Ngoc
    Abstract:

    Polycyclic aromatic hydrocarbons (PAHs) and nanoparticles are expected to play an important role in many astrophysical processes due to its dominant surface area, including gas heating, chemistry, star formation , and anomalous microwave emission. In dense magnetized molecular clouds where C-shocks are present, PAHs and nanoparticles are widely believed to originate from grain shattering due to grain-grain collisions. The remaining question is whether these nanoparticles can survive in the dense and hot shocked regions, and how to constrain their size and abundance with observations. In this paper, we present a new mechanism to destroy nanoparticles in C-shocks based on Centrifugal Stress within rapidly spinning nanoparticles spun-up by stochastic atomic bombardment, which is termed rotational disruption. We find that, due to supersonic neutral gas-charged grain drift in C-shocks, nanoparticles can be spun-up to suprathermal rotation by stochastic torques exerted by supersonic neutral flow. The resulting Centrifugal Stress within suprathermally rotating nanoparticles can exceed the maximum tensile strength of grain material ($S_{\max}$), resulting in rapid disruption of nanoparticles smaller than $a\sim 1$ nm for $S_{\max}\sim 10^{9}\erg\cm^{-3}$. The proposed disruption mechanism is shown to be more efficient than thermal sputtering in controlling the lower cutoff of grain size distribution in C-shocks. We model microwave emission from spinning nanoparticles in C-shocks subject to supersonic neutral drift and rotational disruption. We find that suprathermally rotating nanoparticles can emit strong microwave radiation, and both peak flux and peak frequency increase with increasing the shock velocity. We suggest spinning dust as a new method to constrain nanoparticles and trace shock velocities in dense, shocked regions.Comment: 18 pages, 14 figures; Published in Ap

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    International audienceMassive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈ 1–5 μm) emission excess from H ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR−MIR excess and unusual dust properties is the predominance of small grains (size a ≲ 0.05 μm) relative to large grains (a ≳ 0.1 μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L ≈ 10$^{4}$ L$_{⊙}$, where L$_{⊙}$ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR−MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H ii regions surrounding young massive star clusters

Tram, Le Ngoc - One of the best experts on this subject based on the ideXlab platform.

  • Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL
    2020
    Co-Authors: Tram, Le Ngoc, Hoang Thiem, Lee Hyeseung, Michail, Joseph M., Chuss, David T., Nickerson Sarah, Rangwala Naseem, Reach, William T.
    Abstract:

    Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of $T_{\rm d}\gtrsim 100\,\rm K$. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to Centrifugal Stress induced by radiative torques (RATs) is proposed by Hoang & Tram 2020 that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of three representative COMs which have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for $T_{\rm d}\gtrsim 71\,\rm K$. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.Comment: 13 pages, 9 figures, 1 table, accepted to Ap

  • Rotational Desorption of Ice Mantles and Complex Molecules from Suprathermally Rotating Dust Grains around Young Stellar Objects
    'American Astronomical Society', 2020
    Co-Authors: Hoang Thiem, Tram, Le Ngoc
    Abstract:

    Ice mantles on dust grains play a central role in astrochemistry. Water and complex organic molecules (COMs) are thought to first form on the ice mantles and subsequently are released into the gas phase due to star formation activity. However, the critical question is whether ice mantles can survive stellar radiation when grains are being heated from $T_{d}\sim 10\rm K$ to $\gtrsim 100$ K. In this paper, we first study the effect of suprathermal grain rotation driven by the intense radiation of young stellar objects (YSOs) on the ice mantles. We find that the entire ice mantles can be disrupted into small fragments by Centrifugal Stress before the water ice and COMs desorb via thermal sublimation. We then study the consequence of resulting ice fragments and find that tiny fragments of radius $a \lesssim 10$\AA~ exhibit transient release of COMs due to thermal spikes, whereas larger fragments can facilitate thermal sublimation at much higher rates than from the original icy grain or the same rate but with temperatures of $\sim 20-40$ K lower. We find that rotational desorption is efficient for hot cores/corinos from the inner to outer regions where the temperature drops to $T_{\rm gas}\sim 40\rm K$ and $n_{\rm H}\sim 10^{4}\rm cm^{-3}$. We discuss the implications of this mechanism for desorption of COMs and water ice in various environments, including outflow cavity walls, photodissociation regions, and protoplanetary disks. Finally, we show that very large aggregate grains can be disrupted into individual icy grains via rotational disruption mechanism, followed by rotational desorption of ice mantles.Comment: 17 pages, 11 figures; accepted to Ap

  • Dust Rotational Dynamics in C-shocks: Rotational Disruption of Nanoparticles by Stochastic Mechanical Torques and Spinning Dust Emission
    'American Astronomical Society', 2019
    Co-Authors: Hoang Thiem, Tram, Le Ngoc
    Abstract:

    Polycyclic aromatic hydrocarbons (PAHs) and nanoparticles are expected to play an important role in many astrophysical processes due to its dominant surface area, including gas heating, chemistry, star formation , and anomalous microwave emission. In dense magnetized molecular clouds where C-shocks are present, PAHs and nanoparticles are widely believed to originate from grain shattering due to grain-grain collisions. The remaining question is whether these nanoparticles can survive in the dense and hot shocked regions, and how to constrain their size and abundance with observations. In this paper, we present a new mechanism to destroy nanoparticles in C-shocks based on Centrifugal Stress within rapidly spinning nanoparticles spun-up by stochastic atomic bombardment, which is termed rotational disruption. We find that, due to supersonic neutral gas-charged grain drift in C-shocks, nanoparticles can be spun-up to suprathermal rotation by stochastic torques exerted by supersonic neutral flow. The resulting Centrifugal Stress within suprathermally rotating nanoparticles can exceed the maximum tensile strength of grain material ($S_{\max}$), resulting in rapid disruption of nanoparticles smaller than $a\sim 1$ nm for $S_{\max}\sim 10^{9}\erg\cm^{-3}$. The proposed disruption mechanism is shown to be more efficient than thermal sputtering in controlling the lower cutoff of grain size distribution in C-shocks. We model microwave emission from spinning nanoparticles in C-shocks subject to supersonic neutral drift and rotational disruption. We find that suprathermally rotating nanoparticles can emit strong microwave radiation, and both peak flux and peak frequency increase with increasing the shock velocity. We suggest spinning dust as a new method to constrain nanoparticles and trace shock velocities in dense, shocked regions.Comment: 18 pages, 14 figures; Published in Ap

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    International audienceMassive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈ 1–5 μm) emission excess from H ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR−MIR excess and unusual dust properties is the predominance of small grains (size a ≲ 0.05 μm) relative to large grains (a ≳ 0.1 μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L ≈ 10$^{4}$ L$_{⊙}$, where L$_{⊙}$ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR−MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H ii regions surrounding young massive star clusters

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the universe. Observations usually show near- to mid-infrared (NIR--MIR, $\lambda\sim 1-5~\mu$m) emission excess from H\,{\sc ii} regions around young massive star clusters (YMSCs). Early phase observations in optical to NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The popular explanation for such NIR-MIR excess and unusual dust properties is the predominance of small grains (size $a\lesssim 0.05~\mu$m) relative to large grains ($a\gtrsim 0.1~\mu$m) in the local environment of these strong radiation sources. The question of why small grains are predominant in these environments remains a mystery. Here we report a new mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term the RAdiative Torque Disruption (RATD) mechanism. We find that RATD can disrupt large grains located within a distance of $\sim 1$ pc from a massive star of luminosity $L\sim 10^{4}L_{\odot}$ or a supernova. This effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR-MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within $\sim$ 0.1 pc would be dominated by small grains. Small grains produced by RATD can also explain the steep far-UV rise in extinction curves toward starburst and high redshift galaxies, and the decrease of the escape fraction of Ly$\alpha$ photons from H\,{\sc ii} regions surrounding YMSCs.Comment: Published on 6 May, 201

Lee Hyeseung - One of the best experts on this subject based on the ideXlab platform.

  • Rotational disruption of dust grains by mechanical torques for high-velocity gas-grain collisions
    'American Astronomical Society', 2020
    Co-Authors: Hoang Thiem, Lee Hyeseung
    Abstract:

    Dust grains moving at hypersonic velocities of $v_{d}\gtrsim 100\rm km~s^{-1}$ through an ambient gas are known to be destroyed by nonthermal sputtering. Yet, previous studies of nonthermal sputtering disregarded the fact that dust grains can be spun-up to suprathermal rotation by stochastic mechanical torques from gas-grain collisions. In this paper, we show that such grain suprathermal rotation can disrupt a small grain into small fragments because induced Centrifugal Stress exceeds the maximum tensile strength of grain material, $S_{\rm max}$. We term this mechanism {\it MEchanical Torque Disruption} (METD). We find that METD is more efficient than nonthermal sputtering in destroying smallest grains ($a

  • Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL
    2020
    Co-Authors: Tram, Le Ngoc, Hoang Thiem, Lee Hyeseung, Michail, Joseph M., Chuss, David T., Nickerson Sarah, Rangwala Naseem, Reach, William T.
    Abstract:

    Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of $T_{\rm d}\gtrsim 100\,\rm K$. However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to Centrifugal Stress induced by radiative torques (RATs) is proposed by Hoang & Tram 2020 that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of three representative COMs which have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for $T_{\rm d}\gtrsim 71\,\rm K$. This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.Comment: 13 pages, 9 figures, 1 table, accepted to Ap

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    International audienceMassive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈ 1–5 μm) emission excess from H ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR−MIR excess and unusual dust properties is the predominance of small grains (size a ≲ 0.05 μm) relative to large grains (a ≳ 0.1 μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L ≈ 10$^{4}$ L$_{⊙}$, where L$_{⊙}$ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR−MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H ii regions surrounding young massive star clusters

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the universe. Observations usually show near- to mid-infrared (NIR--MIR, $\lambda\sim 1-5~\mu$m) emission excess from H\,{\sc ii} regions around young massive star clusters (YMSCs). Early phase observations in optical to NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The popular explanation for such NIR-MIR excess and unusual dust properties is the predominance of small grains (size $a\lesssim 0.05~\mu$m) relative to large grains ($a\gtrsim 0.1~\mu$m) in the local environment of these strong radiation sources. The question of why small grains are predominant in these environments remains a mystery. Here we report a new mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term the RAdiative Torque Disruption (RATD) mechanism. We find that RATD can disrupt large grains located within a distance of $\sim 1$ pc from a massive star of luminosity $L\sim 10^{4}L_{\odot}$ or a supernova. This effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR-MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within $\sim$ 0.1 pc would be dominated by small grains. Small grains produced by RATD can also explain the steep far-UV rise in extinction curves toward starburst and high redshift galaxies, and the decrease of the escape fraction of Ly$\alpha$ photons from H\,{\sc ii} regions surrounding YMSCs.Comment: Published on 6 May, 201

Ahn Sang-hyeon - One of the best experts on this subject based on the ideXlab platform.

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    International audienceMassive stars, supernovae, and kilonovae are among the most luminous radiation sources in the Universe. Observations usually show near- to mid-infrared (NIR–MIR, λ ≈ 1–5 μm) emission excess from H ii regions around young massive star clusters. Early-phase observations in optical-to-NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The most common explanation for such NIR−MIR excess and unusual dust properties is the predominance of small grains (size a ≲ 0.05 μm) relative to large grains (a ≳ 0.1 μm) in the local environment of these strong radiation sources. However, why small grains might be predominant in these environments is unclear. Here we report a mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term radiative torque disruption (RATD). We find that RATD can disrupt large grains located within a distance of about a parsec from a massive star of luminosity L ≈ 10$^{4}$ L$_{⊙}$, where L$_{⊙}$ is the solar luminosity, or from a supernova. This disruption effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR−MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within about 0.1 parsec would be dominated by small grains. Small grains produced by RATD can also explain the steep far-ultraviolet rise in extinction curves towards starburst and high-redshift galaxies, and the decrease of the escape fraction of Lyman α photons from H ii regions surrounding young massive star clusters

  • Rotational Disruption of Dust Grains by Radiative Torques in Strong Radiation Fields
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Hoang Thiem, Lee Hyeseung, Tram, Le Ngoc, Ahn Sang-hyeon
    Abstract:

    Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the universe. Observations usually show near- to mid-infrared (NIR--MIR, $\lambda\sim 1-5~\mu$m) emission excess from H\,{\sc ii} regions around young massive star clusters (YMSCs). Early phase observations in optical to NIR wavelengths of type Ia supernovae also reveal unusual properties of dust extinction and dust polarization. The popular explanation for such NIR-MIR excess and unusual dust properties is the predominance of small grains (size $a\lesssim 0.05~\mu$m) relative to large grains ($a\gtrsim 0.1~\mu$m) in the local environment of these strong radiation sources. The question of why small grains are predominant in these environments remains a mystery. Here we report a new mechanism of dust destruction based on Centrifugal Stress within extremely fast-rotating grains spun-up by radiative torques, which we term the RAdiative Torque Disruption (RATD) mechanism. We find that RATD can disrupt large grains located within a distance of $\sim 1$ pc from a massive star of luminosity $L\sim 10^{4}L_{\odot}$ or a supernova. This effect increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR-MIR excess and anomalous dust extinction/polarization. We apply the RATD mechanism for kilonovae and find that dust within $\sim$ 0.1 pc would be dominated by small grains. Small grains produced by RATD can also explain the steep far-UV rise in extinction curves toward starburst and high redshift galaxies, and the decrease of the escape fraction of Ly$\alpha$ photons from H\,{\sc ii} regions surrounding YMSCs.Comment: Published on 6 May, 201

Weifeng Wang - One of the best experts on this subject based on the ideXlab platform.

  • spinoculation triggers dynamic actin and cofilin activity that facilitates hiv 1 infection of transformed and resting cd4 t cells
    Journal of Virology, 2011
    Co-Authors: Jia Guo, Weifeng Wang
    Abstract:

    Centrifugal inoculation, or spinoculation, is widely used in virology research to enhance viral infection. However, the mechanism remained obscure. Using HIV-1 infection of human T cells as a model, we demonstrate that spinoculation triggers dynamic actin and cofilin activity, probably resulting from cellular responses to Centrifugal Stress. This actin activity also leads to the upregulation of the HIV-1 receptor and coreceptor, CD4 and CXCR4, enhancing viral binding and entry. We also demonstrate that an actin inhibitor, jasplakinolide, diminishes spin-mediated enhancement. In addition, small interfering RNA (siRNA) knockdown of LIMK1, a cofilin kinase, decreases the enhancement. These results suggest that spin-mediated enhancement cannot be explained simply by a virus-concentrating effect; rather, it is coupled with spin-induced cytoskeletal dynamics that promote receptor mobilization, viral entry, and postentry processes. Our results highlight the importance of cofilin and a dynamic cytoskeleton for the initiation of viral infection. Our results also indicate that caution needs to be taken in data interpretation when cells are spinoculated; some of the spin-induced cellular permissiveness may be beyond the natural capacity of an infecting virus.