arXiv subjects

Wenrui Xu

Publications and source records attributed to Wenrui Xu.

At least 19 recordsLinked to original sources

arXiv2026

DCRA: Diffusion-Conditioned Representation Alignment for Robust Time-Series Learning

Learning robust representations for time-series signals under noise and distribution shifts remains challenging, especially in clinical applications such as electroencephalogram (EEG) and electrocardiogram (ECG) analysis. We propose Diffusion-Conditioned Representation Alignment (DCRA), a training framework that repurposes the forward diffusion process as a structured corruption scheduler for representation learning. Different from conventional augmentation and consistency-based methods that rely on independently sampled perturbations, DCRA introduces a structured corruption trajectory via the diffusion forward process, which enables continuous and controlled representation evolution across noise levels. We introduce a feature-level consistency objective that aligns representations across noise levels while preserving class-discriminative structure. This mechanism promotes structure-preserving consistency, which enables smooth and semantically coherent feature trajectories in latent space. The proposed framework is encoder-agnostic and can be integrated with state space models and Transformer architectures. The seizure detection experiments on the CHB-MIT EEG dataset show that DCRA consistently improves performance under multiple noise conditions and achieves higher sensitivity at low false-positive rates. Analysis reveals that DCRA produces more balanced and structured representations compared to baseline and diffusion-only models. These findings highlight the benefit of combining structured corruption with representation alignment for robust time-series learning.

cs.LG↗

arXiv2026

Modeling the Evolution of Protoplanetary Disks: Two Pathways from Gravitational Instability to MHD Wind-Driven Accretion

The global evolution of protoplanetary disks sets the initial conditions for planet formation. However, most models focus on individual evolutionary phases, with idealized initial conditions and oversimplified prescriptions for angular momentum transport and thermodynamics. We present a more realistic semi-two-dimensional ($1+1$D) model incorporating gravitational instability (GI), magnetohydrodynamic (MHD) winds, magneto-rotational instability (MRI), stellar irradiation, self-shadowing, and radiation transport. The radial distribution of large-scale magnetic flux drives two different pathways of disk evolution. When the vertical field is spatially uniform, a puffed-up, MRI-heated inner rim shadows the disk beyond it, sustaining a massive, gravitationally unstable region for $\sim 1$ Myr and, for several Myr, a compact ($\lesssim 10$ AU), cold ($\sim10$ K), low-turbulence ($α_\mathrm{SS}\sim10^{-4}$), high-density ($Σ\gtrsim300\,\mathrm{g\,cm^{-2}}$), optically thick reservoir, so that the disk mass inferred from mm-continuum emission can be greatly underestimated. When the field instead scales with midplane gas pressure, it drives stronger transport in the inner disk and eventually strips the shadow, leaving an extended, flared disk whose observable mass closely traces the true mass. Our results connect GI-dominated Class~0/I disks to MHD wind-driven Class~II disks, and point to three broader conclusions: (i) disk physics is strongly inhomogeneous in space and time, so constant-$α$ treatments miss essential physics; (ii) thermodynamics plays an active role, with self-shadowing simultaneously preserving GI and weakening MHD winds; and (iii) the distribution of large-scale magnetic flux is the key uncertainty, closely linked to whether the shadow is maintained. The two pathways align, respectively, with observations of compact, shadowed disks and extended, irradiated disks.

astro-ph.EP↗

arXiv2026

A Vision Toward Energy-Efficient Domain-Specific Artificial Intelligence Models and Agents

The field of artificial intelligence (AI) has taken a tight hold on broad aspects of society, industry, business, and governance in ways that dictate the prosperity and might of the world's economies. The AI market size is projected to grow from {\$}189 billion in 2023 to {\$}4.8 trillion by 2033. Currently, AI is dominated by large language models (LLMs) that exhibit linguistic and visual intelligence. However, training these models requires a massive amount of data scraped from the web as well as large amounts of energy (50-60 GWh to train GPT-4). Despite these costs, these models often hallucinate, a characteristic that prevents them from being deployed in critical application domains. In contrast, the human brain consumes only 20W of power. What is needed is the next level of AI evolution in which lightweight domain-specific multimodal models, especially compact models with 10--20B parameters for bounded domains, with higher levels of intelligence can reason, plan, and make decisions in dynamic environments with real-time data and prior knowledge, while learning continuously and evolving in ways that enhance future decision-making capability. This will define the next wave of AI, progressing from today's large models, trained with vast amounts of data, to nimble energy-efficient domain-specific agents that can reason and think in a world full of uncertainty. To support such agents, hardware will need to be reimagined to allow system-level energy efficiencies $\geq {1000X}$ over the state of the art for targeted domain tasks, subject to accuracy, latency, and coverage constraints. Such a vision of future AI systems is developed in this work.

cs.AI↗

arXiv2026

Turbulent infall onto class 0 disks as cause of CAI brief condensation episode in the solar system

Calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondritic meteorites are the oldest relics in the solar system. Notably, their radiogenic age feature a brief (100 kyr) condensation episode. In contrast, the reservoirs of the short-lived isotopes in CAIs, presumably supernovae or asymptotic giant stars, pollutes star-forming regions in giant molecular cloud complexes (GMC) over much longer (Myr) duration. Through a series of numerical simulations, we show here the possibility that, within an extended region (2$\sim$3 AU), nearly all ``pre-solar'' CAI-loaded grains in the infall clouds were sublimated and re-condensed during the early ($ \lesssim 10^5$ yr) infall and formation of class-0 disks. We adopt a set of initial conditions from a previous hydrodynamic simulation of the collapse of GMC and the formation of young stellar clusters. We analyze the evolution of the disk's thermal distribution and dynamical structure resulting from the interaction between circumstellar disks and infalling gas. Our follow-up simulations, with much higher resolution, show significant and rapid changes in the disk orientation and morphology due to the dynamic infall of external streamers. Warps and global spiral density waves commonly appear. They lead to intense dissipation which heats the gas to sufficiently high temperature to sublimate prior-generation CAIs. This solid-to-gas phase transition is followed by subsequent cooling and re-condensation. The CAI contained in the meteorites today could be the relics of the last episode of major infall onto class 0 disks.

astro-ph.EP↗

arXiv2025

Higher-Order Mean-Motion Resonances Can Form in Type-I Disk Migration

Type-I disk migration can form a chain of planets engaged in first-order mean-motion resonances (MMRs) parked at the disk inner edge. However, while second- or even third-order resonances were deemed unlikely due to their weaker strength, they have been observed in some planetary systems (e.g. TOI-178 bc: 5:3, TOI-1136 ef: 7:5, TRAPPIST-1 bcd: 8:5-5:3). We performed $>6,000$ Type-I simulations of multi-planet systems that mimic the observed {\it Kepler} sample in terms of stellar mass, planet size, multiplicity, and intra-system uniformity over a parameter space encompassing transitional and truncated disks. We found that Type-I migration coupled with a disk inner edge can indeed produce second- and third-order resonances (in a state of libration) in $\sim 10\%$ and 2\% of resonant-chain systems, respectively. Moreover, the relative occurrence of first- and second-order MMRs in our simulations is consistent with observations (e.g. 3:2 is more common than 2:1; while second-order 5:3 is more common than 7:5). The formation of higher-order MMRs favors slower disk migration and a smaller outer planet mass. Higher-order resonances do not have to form with the help of a Laplace-like three-body resonance as was proposed for TRAPPIST-1. Instead, the formation of higher-order resonance is assisted by breaking a pre-existing first-order resonance, which generates small but non-zero initial eccentricities ($e\approx10^{-3}$ to 10$^{-2}$). We predict that 1) librating higher-order resonances have higher equilibrium $e$ ($\sim 0.1$); 2) are more likely found as an isolated pair in an otherwise first-order chain; 3) more likely emerge in the inner pairs of a chain.

astro-ph.EP↗

arXiv2025

A Survey of Attacks on Large Language Models

Large language models (LLMs) and LLM-based agents have been widely deployed in a wide range of applications in the real world, including healthcare diagnostics, financial analysis, customer support, robotics, and autonomous driving, expanding their powerful capability of understanding, reasoning, and generating natural languages. However, the wide deployment of LLM-based applications exposes critical security and reliability risks, such as the potential for malicious misuse, privacy leakage, and service disruption that weaken user trust and undermine societal safety. This paper provides a systematic overview of the details of adversarial attacks targeting both LLMs and LLM-based agents. These attacks are organized into three phases in LLMs: Training-Phase Attacks, Inference-Phase Attacks, and Availability & Integrity Attacks. For each phase, we analyze the details of representative and recently introduced attack methods along with their corresponding defenses. We hope our survey will provide a good tutorial and a comprehensive understanding of LLM security, especially for attacks on LLMs. We desire to raise attention to the risks inherent in widely deployed LLM-based applications and highlight the urgent need for robust mitigation strategies for evolving threats.

cs.CR↗

arXiv2025

Global Simulations of Gravitational Instability in Protostellar Disks with Full Radiation Transport II. Locality of Gravitoturbulence, Clumpy Spirals, and Implications for Observable Substructure

Spiral perturbations in a gravitationally unstable accretion disk regulate disk evolution through angular-momentum transport and heating and provide an observational signature of gravitational instability (GI). We use global 3D simulations to systematically characterize and understand these spiral perturbations. The spiral perturbations and the resulting transport are overall insensitive to the cooling type, with the exception that radiative cooling, especially in the optically thick regime, reduces the amplitude of temperature perturbations. Spiral perturbations are localized around corotation, allowing transport to be approximated by a local $α$ viscosity to zeroth order in aspect ratio ($H/R$), but only after averaging over multiple orbits in time and/or multiple scale heights in space. Meanwhile, large-amplitude perturbations from strong gravitoturbulence can cause $\mathcal O(α^{1/2})$ deviation in the cooling rate of the disk. We develop empirical prescriptions for the angular-momentum transport, heating, and cooling in a gravitoturbulent disk that capture the deviation from a viscous, unperturbed disk to first order in $H/R$ and $α^{1/2}$. The spiral perturbations in saturated gravitoturbulence are clumpy, with dense clumps forming through the nonlinear coupling between multiple modes at different $m$. Observationally, the clumpy gravitoturbulence produced by saturated GI can be mistaken with observational noise or embedded companions, especially under finite resolution. Meanwhile, grand-design spirals with $m$-fold symmetry may be uncommon among disks in saturated gravitoturbulence, and we speculate that they may instead be a signature of recently triggered or decaying GI.

astro-ph.EP↗

arXiv2025

The 4-400 GHz Survey for the 32 Class II Disks in the Taurus Molecular Cloud

We have compiled the $\sim$4-400 GHz broad spectra of 32 Class II protoplanetary disks in the Taurus-Auriga region, which represents the brightest one-third of sources detected in the submillimeter band in this region. The spectra at >20 GHz frequency can be described with a piecewise function: (1) a power law with a spectral index $\sim$2 at >200 GHz, (2) a power law with spectral index in the range 0.3-4.2 at 20-50 GHz, and (3) a transition region in between these two power laws which can be characterized by a sigmoid function. This suggests that the flux densities at >200 GHz and <50 GHz are dominated by distinct emission components. At >200 GHz, the emission is likely dominated by the optically thick dust thermal emission in the bulk of the disks. In some sources that were not detected at 6.8 GHz or 10 GHz, embedded high-density dust substructures may contribute to a significant fraction of the flux densities at 30-50 GHz, and the spectral indices are mostly consistent with 2.0. Although, at 30-50 GHz, free-free and/or synchrotron emission may be significant, and some sources in our sample have spectral indices < 2.0. Based on these results, we hypothesize that high-density dust substructures (e.g., vortices) are often found in resolved Class II protoplanetary disks, and are a precursor to the formation of kilometer-sized planetesimals and rocky planets. They may not present high contrast at >200 GHz frequencies owing to the high optical depth. To probe these dust substructures, high angular resolution observations at <100 GHz are necessary to distinguish them from free-free and synchrotron emission sources. Otherwise, in the analyses of the spatially unresolved spectra, one needs to simultaneously constrain the flux densities of free-free, synchrotron, and dust emission with the observations at $\sim$5-50 GHz.

astro-ph.EP↗

arXiv2025

Defining and Evaluating Visual Language Models' Basic Spatial Abilities: A Perspective from Psychometrics

The Theory of Multiple Intelligences underscores the hierarchical nature of cognitive capabilities. To advance Spatial Artificial Intelligence, we pioneer a psychometric framework defining five Basic Spatial Abilities (BSAs) in Visual Language Models (VLMs): Spatial Perception, Spatial Relation, Spatial Orientation, Mental Rotation, and Spatial Visualization. Benchmarking 13 mainstream VLMs through nine validated psychometric experiments reveals significant gaps versus humans (average score 24.95 vs. 68.38), with three key findings: 1) VLMs mirror human hierarchies (strongest in 2D orientation, weakest in 3D rotation) with independent BSAs (Pearson's r<0.4); 2) Smaller models such as Qwen2-VL-7B surpass larger counterparts, with Qwen leading (30.82) and InternVL2 lagging (19.6); 3) Interventions like chain-of-thought (0.100 accuracy gain) and 5-shot training (0.259 improvement) show limits from architectural constraints. Identified barriers include weak geometry encoding and missing dynamic simulation. By linking psychometric BSAs to VLM capabilities, we provide a diagnostic toolkit for spatial intelligence evaluation, methodological foundations for embodied AI development, and a cognitive science-informed roadmap for achieving human-like spatial intelligence.

cs.CV↗

arXiv2024

Grain Size in the Class I Protostellar System TMC-1A Constrained with ALMA and VLA Observations

The disk mass and substructure in young stellar objects suggest that planet formation may start at the protostellar stage through the growth of dust grains. To accurately estimate the grain size at the protostellar stage, we have observed the Class I protostar TMC-1A using the Jansky Very Large Array (VLA) at the Q (7 mm) and Ka (9 mm) bands at a resolution of ~0.2" and analyzed archival data of Atacama Large Millimeter/submillimeter Array (ALMA) at Band 6 (1.3 mm) and 7 (0.9 mm) that cover the same spatial scale. The VLA images show a compact structure with a size of ~25 au and a spectral index of ~2.5. The ALMA images show compact and extended structures with a spectral index of ~2 at the central ~40 au region and another index of ~3.3 in the outer region. Our SED analysis using the observed fluxes at the four bands suggests one branch with a small grain size of ~0.12 mm and another with a grown grain size of ~4 mm. We also model polarized dust continuum emission adopting the two grain sizes and compare them with an observational result of TMC-1A, suggesting that the small grain size is preferable to the grown grain size. The small grain size implies gravitational instability in the TMC-1A disk, which is consistent with a spiral-like component recently identified.

astro-ph.GA↗

arXiv2024

Global Simulations of Gravitational Instability in Protostellar Disks with Full Radiation Transport. I. Stochastic Fragmentation with Optical-depth-dependent Rate and Universal Fragment Mass

Fragmentation in a gravitationally unstable accretion disk can be an important pathway for forming stellar/planetary companions. To characterize quantitatively the condition for and outcome of fragmentation under realistic thermodynamics, we perform global 3D simulations of gravitationally unstable disks at various cooling rates and cooling types, including the first global simulations of gravitational instability that employ full radiation transport. We find that fragmentation is a stochastic process, with the fragment generation rate per disk area $p_{\rm frag}$ showing an exponential dependence on the parameter $β\equivΩ_K t_{cool}$, where $Ω_K$ is the Keplerian rotation frequency and $t_{cool}$ is the average cooling timescale. Compared to a prescribed constant $β$, radiative cooling in the optically thin/thick regime makes $p_{\rm frag}$ decrease slower/faster in $β$; the critical $β$ corresponding to $\sim 1$ fragment per orbit is $\approx$3, 5, 2 for constant $β$, optically thin, and optically thick cooling, respectively. The distribution function of the initial fragment mass is remarkably insensitive to disk thermodynamics. Regardless of cooling rate and optical depth, the typical initial fragment mass is $m_{frag} \approx 40 M_{tot}h^3$, with $M_{tot}$ being the total (star+disk) mass and $h=H/R$ being the disk aspect ratio. Applying this result to typical Class 0/I protostellar disks, we find $m_{frag}\sim 20 M_J$, suggesting that fragmentation more likely forms brown dwarfs. Given the finite width of the $m_{frag}$ distribution, forming massive planets is also possible.

astro-ph.EP↗

arXiv2024

Recent Surge in Public Interest in Transportation: Sentiment Analysis of Baidu Apollo Go Using Weibo Data

Urban mobility and transportation systems have been profoundly transformed by the advancement of autonomous vehicle technologies. Baidu Apollo Go, a pioneer robotaxi service from the Chinese tech giant Baidu, has recently been widely deployed in major cities like Beijing and Wuhan, sparking increased conversation and offering a glimpse into the future of urban mobility. This study investigates public attitudes towards Apollo Go across China using Sentiment Analysis with a hybrid BERT model on 36,096 Weibo posts from January to July 2024. The analysis shows that 89.56\% of posts related to Apollo Go are clustered in July. From January to July, public sentiment was mostly positive, but negative comments began to rise after it became a hot topic on July 21. Spatial analysis indicates a strong correlation between provinces with high discussion intensity and those where Apollo Go operates. Initially, Hubei and Guangdong dominated online posting volume, but by July, Guangdong, Beijing, and international regions had overtaken Hubei. Attitudes varied significantly among provinces, with Xinjiang and Qinghai showing optimism and Tibet and Gansu expressing concerns about the impact on traditional taxi services. Sentiment analysis revealed that positive comments focused on technology applications and personal experiences, while negative comments centered on job displacement and safety concerns. In summary, this study highlights the divergence in public perceptions of autonomous ride-hailing services, providing valuable insights for planners, policymakers, and service providers. The model is published on Hugging Face at https://huggingface.co/wsqstar/bert-finetuned-weibo-luobokuaipao and the repository on GitHub at https://github.com/GIStudio/trb2024.

cs.SI↗

arXiv2024

SMA 200-400 GHz Survey for Dust Properties in the Icy Class II Disks in the Taurus Molecular Cloud

We present a new SMA survey of 47 Class II sources in the Taurus-Auriga region. Our observations made 12 independent samples of flux densities over the 200-400 GHz frequency range. We tightly constrained the spectral indices of most sources to a narrow range of $2.0\pm0.2$; only a handful of spatially resolved (e.g., diameter $>$250 au) disks present larger spectral indices. The simplest interpretation for this result is that the (sub)millimeter luminosities of all of the observed target sources are dominated by very optically thick (e.g., $τ\gtrsim$5) dust thermal emission. Some previous works that were based on the optically thin assumption thus might have underestimated optical depths by at least one order of magnitude. Assuming DSHARP dust opacities, this corresponds to underestimates of dust masses by a similar factor. Moreover, some population synthesis models show that to explain the observed, narrowly distributed spectral indices, the disks in our selected sample need to have very similar dust temperatures ($T_{\small{dust}}$). Given a specific assumption of median $T_{\small{dust}}$, the maximum grain sizes ($a_{\small{max}}$) can also be constrained, which is a few times smaller than 0.1 mm for $T_{\small{dust}}\sim$100 K and a few mm for $T_{\small{dust}}\sim$24 K. The results may indicate that dust grain growth outside the water snowline is limited by the bouncing/fragmentation barriers. In the Class II disks, the dust mass budget outside of the water snowline may be largely retained instead of being mostly consumed by planet formation. While Class II disks still possess sufficient dust masses to feed planet formation at a later time, it is unknown whether or not dust coagulation and planet formation can be efficient or natural outside of the water snowline.

astro-ph.EP↗

arXiv2024

Testing a New Model of Embedded Protostellar Disks Against Observation: The Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and Gravitationally Unstable

We formulate a parametrized model of embedded protostellar disks and test its ability to estimate disk properties by fitting dust-continuum observations. The main physical assumptions of our model are motivated by a recent theoretical study of protostellar disk formation; these assumptions include that the disk should be marginally gravitationally unstable, and that the dominant dust heating mechanism is internal accretion heating instead of external protostellar irradiation. These assumptions allow our model to reliably estimate the disk mass even when the observed emission is optically thick and to self-consistently determine disk (dust) temperature. Using our model to fit multi-wavelength observations of 156 disks in the VANDAM Orion survey, we find that the majority (57%) of this sample can be fit well by our model. Using our model, we produce new estimates of Orion protostellar disk properties. We find that these disks are generally warm and massive, with a typical star-to-disk mass ratio $M_{\rm d}/M_\star = \mathcal O(1)$ in Class 0/I. We also discuss why our estimates differ from those in previous studies and the implications of our results on disk evolution and fragmentation.

astro-ph.SR↗

arXiv2024

Earths are not Super-Earths, Saturns are not Jupiters: Imprints of pressure-bump planet formation on planetary architectures

In protoplanetary disks, sufficiently massive planets excite pressure bumps, which can then be preferred locations for forming new planet cores. We discuss how this loop may affect the architecture of multi-planet systems, and compare our predictions with observation. Our main prediction is that low-mass planets and giant planets can each be divided into two subpopulations with different levels of mass uniformity. Low-mass planets that can and cannot reach the pebble isolation mass (the minimum mass required to produce a pressure bump) develop into intra-similar "Super-Earths" and more diverse "Earths", respectively. Gas giants that do and do not accrete envelope quickly develop into intra-similar "Jupiters" and more diverse "Saturns", respectively. Super-Earths prefer to form long chains via repeated pressure-bump planet formation, while Jupiter formation is usually terminated at pairs or triplets due to dynamical instability. These predictions are broadly consistent with observations. In particular, we discover a previously overlooked mass uniformity dichotomy among the observed populations of both low-mass planets (Earths vs. Super-Earths) and gas giants (Saturns vs. Jupiters). For low-mass planets, planets well below the pebble isolation mass ($\lesssim 3M_\oplus$ or $\lesssim 1.5 R_\oplus$ for sun-like stars) show significantly higher intra-system pairwise mass difference than planets around the pebble isolation mass. For gas giants, the period ratios of intra-system pairs show a bimodal distribution, which can be interpreted as two subpopulations with different levels of mass uniformity. These findings suggest that pressure-bump planet formation could be an important ingredient in shaping planetary architectures.

astro-ph.EP↗

arXiv2023

Gravitational instability, spiral substructure, and modest grain growth in a typical protostellar disk: Modeling multi-wavelength dust continuum observation of TMC1A

Embedded, Class 0/I protostellar disks represent the initial condition for planet formation. This calls for better understandings of their bulk properties and the dust grains within them. We model multi-wavelength dust continuum observations of the disk surrounding the Class I protostar TMC1A to provide insight on these properties. The observations can be well fit by a gravitationally self-regulated (i.e., marginally gravitationally unstable and internally heated) disk model, with surface density $Σ\sim 1720 (R/10au)^{-1.96} g/cm^2$ and midplane temperature $T_{mid} \sim 185 (R/10au)^{-1.27} K$. The observed disk contains a $m=1$ spiral substructure; we use our model to predict the spiral's pitch angle and the prediction is consistent with the observations. This agreement serves as both a test of our model and strong evidence of the gravitational nature of the spiral. Our model estimates a maximum grain size $a_{max}\sim 196(R/10au)^{-2.45} μm$, which is consistent with grain growth being capped by a fragmentation barrier with threshold velocity $\sim 1 m/s$. We further demonstrate that observational properties of TMC1A are typical among the observed population of Class 0/I disks, which hints that traditional methods of disk data analyses based on Gaussian fitting and the assumption of the optically thin dust emission could have systematically underestimated disk size and mass and overestimated grain size.

astro-ph.SR↗

arXiv2023

Simple convective accretion flows (SCAFs): Explaining the $\approx-1$ density scaling of hot accretion flows around compact accretors

Recent simulations find that hot gas accretion onto compact accretors are often highly turbulent and diskless, and show power-law density profiles with slope $α_ρ\approx-1$. These results are consistent with observational constraints, but do not match existing self-similar solutions of radiatively inefficient accretion flows. We develop a theory for this new class of accretion flows, which we dub simple convective accretion flows (SCAFs). We use a set of hydrodynamic simulations to provide a minimalistic example of SCAFs, and develop an analytic theory to explain and predict key flow properties. We demonstrate that the turbulence in the flow is driven locally by convection, and argue that radial momentum balance, together with an approximate up-down symmetry of convective turbulence, yields $α_ρ=-1\pm~{\rm few}~0.1$. Empirically, for an adiabatic hydrodynamic flow with $γ\approx 5/3$, we get $α_ρ\approx-0.8$; the resulting accretion rate (relative to the Bondi accretion rate), $\dot M/\dot M_{\rm B}\sim (r_{\rm acc}/r_{\rm B})^{0.7}$, agrees very well with the observed accretion rates in Sgr A*, M87*, and a number of wind-fed SgXBs. We also argue that the properties of SCAFs are relatively insensitive to additional physical ingredients such as cooling and magnetic field; this explains its common appearance across simulations of different astrophysical systems.

astro-ph.HE↗

arXiv2023

Revisiting collisional dust growth in Class 0/I protostellar disks: Sweep-up can convert a few $10 M_\oplus$ of dust into kg pebbles in 0.1 Myr

Recent observations suggest that the first stages of planet formation likely take place in the Class 0/I phase of Young Stellar Object evolution, when the star and the disk are still embedded in an infalling envelope. In this study we perform grain coagulation calculations to investigate the very first stage of planet formation, the collisional growth of dust grains, in Class 0/I disks. We find that the slow increase in grain mass by high-velocity collision with much smaller grains ("sweep-up") allows $\sim 50 M_\oplus$ of grains to grow well beyond the fragmentation barrier into $\sim$kg pebbles by the end of Class 0/I (0.1 Myr). We analyze the linear growth and saturation of sweep-up to understand our results quantitatively, and test whether the sweep-up outcome is sensitive to disk parameters and details of the grain coagulation model. The sweep-up pebble population could be important for planet formation, because they are less well-coupled to the gas (compared to the main population below the fragmentation barrier) and therefore more favorable to known mechanisms of dust clump formation (which initiate planetesimal formation). It also contains enough mass to form all planet cores, based on observational estimates of the planet mass budget. Our findings motivate future studies of grain growth and planetesimal formation in Class 0/I disks, including the subsequent evolution of this sweep-up population.

astro-ph.EP↗