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Register a new userThe Dynamics, Destruction, and Survival of Supernova-Formed Dust Grains
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Observations have demonstrated that supernovae efficiently produce dust. This is consistent with the hypothesis that supernovae and asymptotic giant branch stars are the primary producers of dust in the Universe. However, there has been a longstanding question of how much of the dust detected in the interiors of young supernova remnants can escape into the interstellar medium. We present new hydrodynamical calculations of the evolution of dust grains that were formed in dense ejecta clumps within a Cas A-like remnant. We follow the dynamics of the grains as they decouple from the gas after their clump is hit by the reverse shock. They are subsequently subject to destruction by thermal and kinetic sputtering as they traverse the remnant. Grains that are large enough ($sim 0.25,mu$m for silicates and $sim 0.1,mu$m for carbonaceous grains) escape into the interstellar medium while smaller grains get trapped and destroyed. However, grains that reach the interstellar medium still have high velocities, and are subject to further destruction as they are slowed down. We find that for initial grain size distributions that include large ($sim 0.25 - 0.5,mu$m) grains, 10--20% of silicate grains can survive, while 30--50% of carbonaceous grains survive even when the initial size distribution cuts off at smaller ($0.25,mu$m) sizes. For a 19 M$_{odot}$ star similar to the progenitor of Cas A, up to 0.1 M$_{odot}$ of dust can survive if the dust grains formed are large. Thus we show that supernovae under the right conditions can be significant sources of interstellar dust.
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Supernovae (SNe) have been proposed to be the main production sites of dust grains in the Universe. Our knowledge on their importance to dust production is, however, limited by observationally poor constraints on the nature and amount of dust particles produced by individual SNe. In this paper, we present a spectrum covering optical through near-Infrared (NIR) light of the luminous Type IIn supernova (SN IIn) 2010jl around one and half years after the explosion. This unique data set reveals multiple signatures of newly formed dust particles. The NIR portion of the spectrum provides a rare example where thermal emission from newly formed hot dust grains is clearly detected. We determine the main population of the dust species to be carbon grains at a temperature of ~1,350 - 1,450K at this epoch. The mass of the dust grains is derived to be ~(7.5 - 8.5) x 10^{-4} Msun. Hydrogen emission lines show wavelength-dependent absorption, which provides a good estimate on the typical size of the newly formed dust grains (~0.1 micron, and most likely <~0.01 micron). We attribute the dust grains to have been formed in a dense cooling shell as a result of a strong SN-circumstellar media (CSM) interaction. The dust grains occupy ~10% of the emitting volume, suggesting an inhomogeneous, clumpy structure. The average CSM density is required to be >~3 x 10^{7} cm^{-3}, corresponding to a mass loss rate of >~0.02 Msun yr^{-1} (for a mass loss wind velocity of ~100 km s^{-1}). This strongly supports a scenario that SN 2010jl and probably other luminous SNe IIn are powered by strong interactions within very dense CSM, perhaps created by Luminous Blue Variable (LBV)-like eruptions within the last century before the explosion.
We report the discovery of an SN1988Z-like type IIn supernova KISS15s found in a low-mass star-forming galaxy at redshift z=0.038 during the course of the Kiso Supernova Survey (KISS). KISS15s shows long-duration optical continuum and emission line light curves, indicating that KISS15s is powered by a continuous interaction between the expanding ejecta and dense circumstellar medium (CSM). The H$alpha$ emission line profile can be decomposed into four Gaussians of narrow, intermediate, blue-shifted intermediate, and broad velocity width components, with a full width at half maximum of $lesssim 100$, $sim 2,000$, and $sim 14,000$ km s${}^{-1}$ for the narrow, intermediate, and broad components, respectively. The presence of the blue-shifted intermediate component, of which the line-of-sight velocity relative to the systemic velocity is about $-5,000$ km s${}^{-1}$, suggests that the ejecta-CSM interaction region has an inhomogeneous morphology and anisotropic expansion velocity. We found that KISS15s shows increasing infrared continuum emission, which can be interpreted as hot dust thermal emission of $T sim 1,200$ K from newly formed dust in a cool, dense shell in the ejecta-CSM interaction region. The progenitor mass-loss rate, inferred from bolometric luminosity, is $dot{M} sim 0.4 M_{odot} text{yr}^{-1} (v_{w}/40 text{km}~text{s}^{-1})$, where $v_{w}$ is the progenitors stellar wind velocity. This implies that the progenitor of KISS15s was a red supergiant star or a luminous blue variable that had experienced a large mass-loss in the centuries before the explosion.
The presence of short-lived radioisotopes (SLRs) in solar system meteorites has been interpreted as evidence that the solar system was exposed to a supernova shortly before or during its formation. Yet results from hydrodynamical models of SLR injection into the proto-solar cloud or disc suggest that gas-phase mixing may not be efficient enough to reproduce the observed abundances. As an alternative, we explore the injection of SLRs via dust grains as a way to overcome the mixing barrier. We numerically model the interaction of a supernova remnant containing SLR-rich dust grains with a nearby molecular cloud. The dust grains are subject to drag forces and both thermal and non-thermal sputtering. We confirm that the expanding gas shell stalls upon impact with the dense cloud and that gas-phase SLR injection occurs slowly due to hydrodynamical instabilities at the cloud surface. In contrast, dust grains of sufficient size (> 1 micron) decouple from the gas and penetrate into the cloud within 0.1 Myr. Once inside the cloud, the dust grains are destroyed by sputtering, releasing SLRs and rapidly enriching the dense (potentially star-forming) regions. Our results suggest that SLR transport on dust grains is a viable mechanism to explain SLR enrichment.
In Spitzer observations of Tauri stars and their disks, PAH features are detected in less than 10% of the objects, although the stellar photosphere is sufficiently hot to excite PAHs. To explain the deficiency, we discuss PAH destruction by photons assuming that the star has beside its photospheric emission also a FUV, an EUV and an X-ray component with fractional luminosity of 1%, 0.1% and 0.025%, respectively. As PAH destruction process we consider unimolecular dissociation and present a simplified scheme to estimate the location from the star where the molecules become photo-stable. We find that soft photons with energies below ~20eV dissociate PAHs only up to short distances from the star (r < 1AU); whereas dissociation by hard photons (EUV and X-ray) is so efficient that it would destroy all PAHs (from regions in the disk where they could be excited). As a possible path for PAH survival we suggest turbulent motions in the disk. They can replenish PAHs or remove them from the reach of hard photons. For standard disk models, where the surface density changes like 1/r and the mid plane temperature like 1/r^{0.5}, the critical vertical velocity for PAH survival is proportional to r^{-3/4} and equals ~5m/s at 10AU which is in the range of expected velocities in the surface layer. The uncertainty in the parameters is large enough to explain both detection and non-detection of PAHs. Our approximate treatment also takes into account the presence of gas which, at the top of the disk, is ionized and at lower levels neutral.
We study the dust evolution in the supernova remnant Cassiopeia A. We follow the processing of dust grains that formed in the Type II-b supernova by modelling the sputtering of grains. The dust is located in dense ejecta clumps crossed by the reverse shock. Further sputtering in the inter-clump medium once the clumps are disrupted by the reverse shock is investigated. The dust evolution in the dense ejecta clumps of Type II-P supernovae and their remnants is also studied. We study oxygen-rich clumps that describe the ejecta oxygen core, and carbon-rich clumps that correspond to the outermost carbon-rich ejecta zone. We consider the dust components formed in the supernova, several reverse shock velocities and inter-clump gas temperatures, and derive dust grain size distributions and masses as a function of time. We find that non-thermal sputtering in clumps is important and accounts for reducing the grain population by ~ 40% to 80% in mass, depending on the clump gas over-density and the grain type and size. A Type II-b supernova forms small grains that are sputtered within clumps and in the inter-clump medium. For Cas A, silicate grains do not survive thermal sputtering in the inter-clump medium. Our derived masses of currently processed silicate, alumina and carbon grains in Cas A agree well with values derived from observations. Grains produced by Type II-P supernovae better survive the remnant phase. For dense ejecta clumps, dust survival efficiencies range between 42% and 98% in mass. For the SN1987A model, the derived surviving dust mass is in the range ~ 0.06-0.13 Msolar. This type of dense supernovae may efficiently provide galaxies with dust. Specifically, silicate grains over 0.1 micron and other grains over 0,05 micron survive thermal sputtering in the remnant. Therefore, pre-solar grains of supernova origin possibly form in the dense ejecta clumps of Type II-P supernovae.
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