Radiation Hydrodynamics of Self-gravitating Protoplanetary Disks II. Accretion, Migration, Spin, and Internal Structure of GI Fragments
Abstract
In the first paper of this series, we showed that gravitational instability (GI) in protoplanetary disks can produce fragments of planetary rather than brown-dwarf mass, leaving the subsequent evolution and ultimate fates of such fragments an open question. Here, we follow every bound object in a global three-dimensional radiation hydrodynamic simulation of a fragmenting 0.196 M⊙ disk around a 1 M⊙ star: seven surviving fragments, one disrupted clump, and one merged clump, followed for $1.2$\,kyr. The fragments form at $1.4−−3.0\,M_\mathrm{J}$, consistent with the normalized initial-mass distribution of Paper~I. Mass growth follows a single Hill-limited scaling ∝ ΣΩRH2, regulated by the delivery of gas into draining feeding zones, while the latest-forming fragments experience supply starvation. Migration is bidirectional and governed by gravitational interactions with both the disk and neighboring clumps. Accretion supplies most of the fragments' spin, which aligns with their orbits and provides roughly a tenth of the support against gravity. The interiors are entropy-stratified, largely convectively stable, and accumulate mass far faster than they can radiatively cool: compression is quasi-adiabatic, and central entropies near 12 kB per baryon favor hot-start initial conditions for fragments that evolve into gas giants. Integrating the measured growth law against the measured gas budget, we predict that the disk produces gas giants, brown dwarfs, and a possible low-mass stellar companion, while one scattered fragment may become a free-floating planet: the outcome of disk fragmentation is determined not merely at birth, but by the subsequent mass supply and dynamics.
Related
- Secular evolution of viscous and self-gravitating protoplanetary discs with magnetic winds
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- The Limited Lifetime of Self-Gravitating Accretion Disks In Galactic Centers
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BibTeX
@misc{ni2026radiation,
title = {{Radiation Hydrodynamics of Self-gravitating Protoplanetary Disks II. Accretion, Migration, Spin, and Internal Structure of GI Fragments}},
author = {Yang Ni and Hongping Deng and Xue-Ning Bai},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.37984},
eprint = {2609.37984},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.37984},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Radiation Hydrodynamics of Self-gravitating Protoplanetary Disks II. Accretion, Migration, Spin, and Internal Structure of GI Fragments
AU - Yang Ni
AU - Hongping Deng
AU - Xue-Ning Bai
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.37984
UR - https://arxiv.org/abs/2609.37984
AB - In the first paper of this series, we showed that gravitational instability (GI) in protoplanetary disks can produce fragments of planetary rather than brown-dwarf mass, leaving the subsequent evolution and ultimate fates of such fragments an open question. Here, we follow every bound object in a global three-dimensional radiation hydrodynamic simulation of a fragmenting 0.196 M_⊙ disk around a 1 M_⊙ star: seven surviving fragments, one disrupted clump, and one merged clump, followed for $1.2$\,kyr. The fragments form at $1.4−−3.0\,M_\mathrm{J}$, consistent with the normalized initial-mass distribution of Paper~I. Mass growth follows a single Hill-limited scaling ∝ ΣΩR_H^2, regulated by the delivery of gas into draining feeding zones, while the latest-forming fragments experience supply starvation. Migration is bidirectional and governed by gravitational interactions with both the disk and neighboring clumps. Accretion supplies most of the fragments' spin, which aligns with their orbits and provides roughly a tenth of the support against gravity. The interiors are entropy-stratified, largely convectively stable, and accumulate mass far faster than they can radiatively cool: compression is quasi-adiabatic, and central entropies near 12 k_B per baryon favor hot-start initial conditions for fragments that evolve into gas giants. Integrating the measured growth law against the measured gas budget, we predict that the disk produces gas giants, brown dwarfs, and a possible low-mass stellar companion, while one scattered fragment may become a free-floating planet: the outcome of disk fragmentation is determined not merely at birth, but by the subsequent mass supply and dynamics.
ER -