Coevolution of Dust Growth and Gravitational Instability in Massive Protostellar Disks

Ryota Yamamuro; Ryoki Matsukoba; Kei E. I. Tanaka; Eduard I. Vorobyov

doi:10.3847/1538-4357/aeacdd

AI summary · arXiv: 2610.28331v1 · astro-ph.SR

Coevolution of Dust Growth and Gravitational Instability in Massive Protostellar Disks

Ryota Yamamuro, Ryoki Matsukoba, Kei E. I. Tanaka, Eduard I. Vorobyov

Original paper · DOI 10.3847/1538-4357/aeacdd Submitted to arXiv on 20 Oct. 2026 Published in The Astrophysical Journal (30 Oct. 2026) Accepted on 25 Sep. 2026 21 pages, 9 figures,accepted for publication to The Astrophysical Journal License: CC BY 4.0 Also in: fr

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The essentials

The study models how dust growth and gravitational instability interact in massive protostellar disks, using self-consistent, two-dimensional gas-and-dust simulations of a collapsing 30-solar-mass cloud core.
Two otherwise identical models compare evolving dust grains with grains fixed at a maximum radius of 1 micrometer.
Dust grows to millimeter–centimeter sizes within a few thousand years of disk formation, with substantial growth across most of the inner 300 astronomical units by 150,000 years.
Grain growth lowers infrared opacity by one to two orders of magnitude, enhancing cooling in the mostly optically thick disk and promoting fragmentation.
Final stellar masses remain similar—approximately 19 solar masses with dust growth and 18 without—but dust growth greatly increases accretion variability.
Peak accretion rates reach 0.2 solar masses per year with dust growth versus 0.006 without; high-rate episodes contribute approximately 20 percent versus 6 percent of the final stellar mass.
The dust-growth model produces 248 luminosity bursts versus 44 without growth, with peak luminosities of approximately 10,000–10 million solar luminosities and durations from one year to several tens of years.
Frequent collisions generally limit grain growth through fragmentation in dense regions, supporting azimuthally averaged steady models; grains in low-density regions can exceed the local fragmentation limit because destructive collisions are infrequent.
Dust growth intensifies fragmentation and episodic accretion and may encourage multiple-star formation, but it is not necessary for accretion bursts.
Quantitative predictions remain limited by two-dimensional geometry, unresolved processes within 5 astronomical units, simplified dust physics, uncertain fragmentation thresholds, and omitted magnetic and radiative processes.

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AI-generated keywords: Dust growth; Gravitational instability; Massive protostellar disks; Episodic accretion; Disk fragmentation

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Original abstract

This paper investigates the interplay between dust growth and gravitational instability in massive protostellar disks. These disks must transport material rapidly enough to sustain the high accretion rates required for massive-star formation. Their self-gravity can produce spiral arms, fragmentation, and episodic accretion, while dust growth alters opacity and cooling efficiency. Earlier steady, axisymmetric models suggested that dust growth could promote instability but could not capture how evolving spiral arms and clumps regulate grain growth. This study therefore examines these feedback processes self-consistently in a dynamically evolving disk. The authors use FEOSAD, a two-dimensional hydrodynamics code employing the thin-disk approximation, to simulate the collapse of a rotating, 30-solar-mass cloud core and the subsequent formation of a protostar and disk. Gas and dust are modeled as interacting fluids, with separate small- and grown-grain components. Grain sizes evolve through coagulation, fragmentation, and transport, with fragmentation occurring over finite collision times rather than instantaneously. Grain-size-dependent opacities govern radiative heating and cooling. The simulations employ a 512-by-512 polar grid spanning 5–30,000 astronomical units, a turbulence parameter of 0.01, and a dust fragmentation threshold of 10 meters per second. Two otherwise identical models are compared: one allows dust growth, while the other fixes the maximum grain radius at 1 micrometer. The disk forms approximately 37,000 years after collapse begins, and dust reaches millimeter–centimeter sizes within the next few thousand years. By 150,000 years, substantial grain growth extends across most of the inner 300 astronomical units. At temperatures above approximately 100 kelvin, which characterize most of the disk, grain growth reduces infrared opacity. Opacities in the dust-growth model are one to two orders of magnitude lower than in the fixed-grain model. Because most of the disk remains optically thick, this reduction enhances cooling, lowers temperatures, and promotes fragmentation. Despite these differences, overall stellar growth remains similar: the final stellar masses are approximately 19 solar masses with dust growth and 18 solar masses without it. The strongest differences appear in accretion variability. During the main accretion phase, between 37,000 and 150,000 years, both models typically accrete at approximately 0.0001 solar masses per year. Peak rates, however, reach 0.2 solar masses per year with dust growth, compared with 0.006 solar masses per year without it. Accretion at rates above 0.001 solar masses per year contributes approximately 20 percent of the final stellar mass in the dust-growth model, versus 6 percent in the fixed-grain model. The dust-growth simulation produces 248 luminosity bursts, compared with 44 in the model without growth. Peak burst luminosities range from approximately 10,000 to 10 million solar luminosities, with durations spanning one year to several tens of years. Some bursts resemble observed outbursts from massive protostars. In dense regions, grain growth is generally fragmentation-limited because collisions occur frequently enough to constrain grain sizes before transport removes the grains. Despite nonaxisymmetric gas structures, grain sizes can therefore approach an azimuthally averaged fragmentation limit, supporting the usefulness of steady models. Newly formed outer regions have insufficient time for substantial growth. Conversely, grains transported into low-density regions can exceed the local fragmentation limit because destructive collisions are infrequent. The authors conclude that dust growth can intensify disk fragmentation and episodic accretion and may encourage multiple-star formation, although it is not required for accretion bursts to occur. Important limitations include the two-dimensional geometry, unresolved processes within 5 astronomical units, simplified grain compositions and size distributions, and uncertain fragmentation thresholds. The simulations also omit bouncing, sublimation, radiation pressure, photoevaporation, and magnetic effects. These limitations constrain quantitative predictions and motivate more comprehensive three-dimensional studies.

How Growing Dust Grains Can Fuel Outbursts From Massive Young Stars

Building a massive star requires a sustained supply of material, but the journey from cloud to star is anything but smooth. Gas collects in a rotating disk, where gravity can create spiral arms and dense clumps. When material rushes inward, the young star can flare dramatically. New simulations explore how a seemingly small ingredient—growing dust grains—can make these feeding episodes much more extreme.

The study connects dust evolution with the changing structure of a massive protostellar disk. Its central finding is that grain growth can lower opacity, help the disk cool, and encourage fragmentation. The result is not a substantially heavier star, but a more turbulent path to assembling one.

Why Dust Matters to a Self-Gravitating Disk

Massive protostellar disks must move material inward quickly enough to sustain rapid stellar growth. Their own gravity helps drive that transport, producing spiral structures and sometimes breaking the disk into clumps. Whether the disk fragments depends partly on how effectively it can lose heat: pressure resists gravitational collapse, while cooling weakens that support.

Dust helps control this thermal balance by absorbing and emitting radiation. As grains grow, their opacity changes, altering how radiation moves through the disk. Earlier steady, axisymmetric models suggested that growth could promote gravitational instability. But those calculations could not fully capture the feedback between evolving spiral arms, moving clumps, and grains that grow or break apart along the way.

Simulating a Disk That Evolves With Its Dust

The researchers used FEOSAD, a two-dimensional hydrodynamics code with a thin-disk approximation, to follow the collapse of a rotating cloud core containing 30 solar masses. The calculation tracked the formation of a protostar and its surrounding disk, treating gas and dust as interacting fluids.

Dust was divided into small- and grown-grain components. Grain sizes changed through coagulation, fragmentation, and transport. Crucially, destructive collisions took a finite amount of time rather than instantly forcing grains below a prescribed size. Grain-size-dependent opacities linked this evolution to radiative heating and cooling.

Two otherwise identical simulations provided the comparison: one allowed dust growth, while the other kept the maximum grain radius fixed at one micrometer. Both used a 512-by-512 polar grid covering distances from 5 to 30,000 astronomical units, a turbulence parameter of 0.01, and a fragmentation threshold of 10 meters per second.

Larger Grains, Cooler Disks, Stronger Fragmentation

The disk formed approximately 37,000 years after collapse began. Within the next few thousand years, dust reached millimeter-to-centimeter sizes. By 150,000 years, substantial growth extended across most of the inner 300 astronomical units.

At temperatures above roughly 100 kelvin—conditions found throughout most of this disk—grain growth reduced infrared opacity. Opacities in the growth simulation were one to two orders of magnitude lower than in the fixed-grain model.

Lower opacity does not always mean faster cooling, but most of the simulated disk remained optically thick. Under those conditions, reduced opacity allowed heat to escape more effectively. The disk became cooler and more susceptible to fragmentation, strengthening the supply of dense structures that could trigger intense accretion events.

Similar Stellar Masses, Very Different Feeding Histories

Despite their different disk behavior, the simulations produced similar final stellar masses: approximately 19 solar masses with dust growth and 18 without it. The sharper contrast was how that mass arrived.

During the main accretion phase, from about 37,000 to 150,000 years, both models typically supplied material at roughly 0.0001 solar masses per year. Their extremes differed dramatically:

Peak accretion reached 0.2 solar masses per year with dust growth, compared with 0.006 without growth.
Accretion above 0.001 solar masses per year supplied about 20 percent of the final stellar mass in the growth model, versus 6 percent in the comparison model.
The dust-growth simulation produced 248 luminosity bursts, compared with 44 in the fixed-grain simulation.

Peak burst luminosities ranged from approximately 10,000 to 10 million solar luminosities, with events lasting from one year to several tens of years. Some resembled observed outbursts from massive protostars, although resemblance alone does not establish an identical physical origin.

Where Grain Growth Meets Its Limits

In dense regions, frequent destructive collisions generally limited grain sizes before transport could remove them. Despite the disk’s irregular structures, grain sizes could therefore approach an azimuthally averaged fragmentation limit, supporting the usefulness of simpler steady models in those conditions.

Elsewhere, timing mattered. Newly formed outer regions had too little time for substantial growth. Grains transported into low-density regions could instead exceed the local fragmentation limit because destructive collisions were too infrequent to break them down promptly.

A Powerful Feedback, With Important Caveats

The study suggests that dust growth can intensify fragmentation and episodic accretion, and may encourage multiple-star formation. It is not essential for bursts, however: the fixed-grain model also produced them.

Quantitative predictions remain limited by the two-dimensional geometry, unresolved processes inside 5 astronomical units, simplified dust properties, and uncertain fragmentation thresholds. Bouncing, sublimation, radiation pressure, photoevaporation, and magnetic effects were also omitted. More comprehensive three-dimensional studies will be needed, but the message is clear: dust evolution can reshape the dramatic way massive stars acquire their mass.

Created on 21 Oct. 2026

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Coevolution of Dust Growth and Gravitational Instability in Massive Protostellar Disks

The essentials

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Definitions

How Growing Dust Grains Can Fuel Outbursts From Massive Young Stars

Why Dust Matters to a Self-Gravitating Disk

Simulating a Disk That Evolves With Its Dust

Larger Grains, Cooler Disks, Stronger Fragmentation

Similar Stellar Masses, Very Different Feeding Histories

Where Grain Growth Meets Its Limits

A Powerful Feedback, With Important Caveats

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