Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOne Solution to the Mass Budget Problem for Planet Formation: Optically Thick Disks with Dust Scattering
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
ALMA surveys have suggested that the dust in Class II disks may not be enough to explain the averaged solid mass in exoplanets, under the assumption that the mm disk continuum emission is optically thin. This optically thin assumption seems to be supported by recent DSHARP observations where the measured optical depths of spatially resolved disks are mostly less than one. However, we point out that dust scattering can considerably reduce the emission from an optically thick region. If that scattering is ignored, the optical depth will be considerably underestimated. An optically thick disk with scattering can be misidentified as an optically thin disk. Dust scattering in more inclined disks can reduce the intensity even further, making the disk look even fainter. The measured optical depth of $sim$0.6 in several DSHARP disks can be naturally explained by optically thick dust with an albedo of $sim$0.9 at 1.25 mm. Using the DSHARP opacity, this albedo corresponds to a dust population with the maximum grain size ($s_{max}$) of 0.1-1 mm. For optically thick scattering disks, the measured spectral index $alpha$ can be either larger or smaller than 2 depending on if the dust albedo increases or decreases with wavelength. Using the DSHARP opacity, $alpha<2$ corresponds to $s_{max}$ of 0.03-0.3 mm. We describe how this optically thick scattering scenario could explain the observed scaling between submm continuum sizes and luminosities, and might help ease the tension between the dust size constraints from polarization and dust continuum measurements. We suggest that a significant amount of disk mass can be hidden from ALMA observations at short millimeter wavelengths. For compact disks smaller than 30 au, we can easily underestimate the dust mass by more than a factor of 10. Longer wavelength observations (e.g. VLA or SKA) are desired to probe the dust mass in disks.
rate research
Read More
In this work, we study how the dust coagulation/fragmentation will influence the evolution and observational appearances of vortices induced by a massive planet embedded in a low viscosity disk by performing global 2D high-resolution hydrodynamical simulations. Within the vortex, due to its higher gas surface density and steeper pressure gradients, dust coagulation, fragmentation and drift (to the vortex center) are all quite efficient, producing dust particles ranging from micron to $sim 1.0 {rm cm}$, as well as overall high dust-to-gas ratio (above unity). In addition, the dust size distribution is quite non-uniform inside the vortex, with the mass weighted average dust size at the vortex center ($sim 4.0$ mm) being a factor of $sim10$ larger than other vortex regions. Both large ($sim$ mm) and small (tens of micron) particles contribute strongly to affect the gas motion within the vortex. As such, we find that the inclusion of dust coagulation has a significant impact on the vortex lifetime and the typical vortex lifetime is about 1000 orbits. After the initial gaseous vortex is destroyed, the dust spreads into a ring with a few remaining smaller gaseous vortices with a high dust concentration and a large maximum size ($sim$ mm). At late time, the synthetic dust continuum images for the coagulation case show as a ring inlaid with several hot spots at 1.33 mm band, while only distinct hot spots remain at 7.0 mm.
The characterization of exoplanets and their birth protoplanetary disks has enormously advanced in the last decade. Benefitting from that, our global understanding of the planet formation processes has been substantially improved. In this review, we first summarize the cutting-edge states of the exoplanet and disk observations. We further present a comprehensive panoptic view of modern core accretion planet formation scenarios, including dust growth and radial drift, planetesimal formation by the streaming instability, core growth by planetesimal accretion and pebble accretion. We discuss the key concepts and physical processes in each growth stage and elaborate on the connections between theoretical studies and observational revelations. Finally, we point out the critical questions and future directions of planet formation studies.
In recent years evidence has been building that planet formation starts early, in the first $sim$ 0.5 Myr. Studying the dust masses available in young disks enables understanding the origin of planetary systems since mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities. Using the DIANA opacity model including large grains, with a dust opacity value of $kappa_{rm 9 mm}$ = 0.28 cm$^{2}$ g$^{-1}$, the median dust masses of the embedded disks in Perseus are 158 M$_oplus$ for Class 0 and 52 M$_oplus$ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M$_oplus$ and 12 M$_oplus$ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value $kappa_{rm 1.3mm}$ = 2.3 cm$^{2}$ g$^{-1}$. The dust masses of young Class 0 and I disks are larger by at least a factor of 10 and 3, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of $sim$ 15%. Higher efficiency of $sim$ 30% is necessary if the planet formation is set to start in Class I disks.
Circumstantial evidence suggests that most known extra-solar planetary systems are survivors of violent dynamical instabilities. Here we explore how giant planet instabilities affect the formation and survival of terrestrial planets. We simulate planetary system evolution around Sun-like stars from initial conditions that comprise: an inner disk of planetesimals and planetary embryos, three giant planets at Jupiter-Saturn distances, and a massive outer planetesimal disk. We then calculate dust production rates and debris disk SEDs assuming that each planetesimal particle represents an ensemble of smaller bodies in collisional equilibrium. We predict a strong correlation between the presence of terrestrial planets and debris disks, mediated by the giant planets. Strong giant planet instabilities destroy all rocky material - including fully-formed terrestrial planets if the instabilities occur late - along with the icy planetesimals. Stable or weakly unstable systems allow terrestrial planets to accrete and significant dust to be produced in their outer regions. Stars older than ~100 Myr with bright cold dust emission (at ~70 microns) signpost the dynamically calm environments conducive to efficient terrestrial accretion. We predict that while the typical eccentricities of terrestrial planets are small, there should exist a novel class of terrestrial planet system whose single planet undergoes large amplitude oscillations in eccentricity and inclination. By scaling to the observed semimajor axis distribution of giant exoplanets, we estimate that terrestrial exoplanets in the same systems should be a few times more abundant at 0.5 AU than giant or terrestrial exoplanets at 1 AU. Finally, we discuss the Solar System, which appears to be unusual in combining a rich terrestrial planet system with a low dust content.
Planet formation is thought to occur in discs around young stars by the aggregation of small dust grains into much larger objects. The growth from grains to pebbles and from planetesimals to planets is now fairly well understood. The intermediate stage has however been found to be hindered by the radial-drift and fragmentation barriers. We identify a powerful mechanism in which dust overcomes both barriers. Its key ingredients are i) backreaction from the dust onto the gas, ii) grain growth and fragmentation, and iii) large-scale gradients. The pile-up of growing and fragmenting grains modifies the gas structure on large scales and triggers the formation of pressure maxima, in which particles are trapped. We show that these self-induced dust traps are robust: they develop for a wide range of disc structures, fragmentation thresholds and initial dust-to-gas ratios. They are favored locations for pebbles to grow into planetesimals, thus opening new paths towards the formation of planets.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
