Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots
- 1Princeton University
- 2Max-Planck-Institut für extraterrestrische Physik
- 3Flatiron Institute
Abstract
We revisit the spectral appearance of extended self-gravitating accretion disks surrounding compact central objects such as supermassive black holes. Using dust-poor opacities, we show that all optically thick disk solutions possess a universal outer effective temperature of T eff ∼ 4000–4500K, closely resembling compact, high-redshift sources known as little red dots (LRDs). Assuming the extended disk is primarily heated by stellar sources, this “disk Hayashi limit” fixes the dominant optical continuum temperature of the disk spectrum independent of accretion rate M ̇ , central mass M • , and disk viscosity α , and removes the parameter-tuning required in previous disk interpretations of LRDs. The formation and accretion of embedded stellar objects can both power the emission of the outer disk and hollow out the inner disk, suppressing variable UV/X-ray associated with a standard quasar. The resulting disk emission is dominated by a luminous optical continuum, while a separate, nonvariable UV component arises from stellar populations on the nuclear to galaxy scale. We map the optimal region of parameter space for such systems and show that LRD-like appearances naturally emerge for M ̇ / α ≳ 0.1 M ⊙ yr - 1 , a threshold insensitive to M • , below which the system may transition into classical non-self-gravitating active galactic nucleus (AGN) disks, potentially a later evolution stage. We expect this transition to be accompanied by the enhancement of metallicity and production of dust, giving rise to far-infrared emission. This picture offers a physically motivated and quantitative framework connecting LRDs with AGNs and their associated nuclear stellar population.
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BibTeX
@article{chen2026spectral,
title = {{Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots}},
author = {Yi-Xian Chen and Hanpu Liu and Ruancun Li and Bingjie Wang and Yilun Ma and Yan-Fei Jiang and Jenny E. Greene and Eliot Quataert and Jeremy Goodman},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = may,
doi = {10.3847/2041-8213/ae6b69},
url = {https://doi.org/10.3847/2041-8213/ae6b69},
note = {CC BY},
}
RIS
TY - JOUR
TI - Spectral Appearance of Self-gravitating Disks Powered by Stellar Objects: Universal Effective Temperature in the Optical Continuum and Application to Little Red Dots
AU - Yi-Xian Chen
AU - Hanpu Liu
AU - Ruancun Li
AU - Bingjie Wang
AU - Yilun Ma
AU - Yan-Fei Jiang
AU - Jenny E. Greene
AU - Eliot Quataert
AU - Jeremy Goodman
PY - 2026
DA - 2026/05/29
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/ae6b69
UR - https://doi.org/10.3847/2041-8213/ae6b69
AB - We revisit the spectral appearance of extended self-gravitating accretion disks surrounding compact central objects such as supermassive black holes. Using dust-poor opacities, we show that all optically thick disk solutions possess a universal outer effective temperature of T eff ∼ 4000–4500K, closely resembling compact, high-redshift sources known as little red dots (LRDs). Assuming the extended disk is primarily heated by stellar sources, this “disk Hayashi limit” fixes the dominant optical continuum temperature of the disk spectrum independent of accretion rate M ̇ , central mass M • , and disk viscosity α , and removes the parameter-tuning required in previous disk interpretations of LRDs. The formation and accretion of embedded stellar objects can both power the emission of the outer disk and hollow out the inner disk, suppressing variable UV/X-ray associated with a standard quasar. The resulting disk emission is dominated by a luminous optical continuum, while a separate, nonvariable UV component arises from stellar populations on the nuclear to galaxy scale. We map the optimal region of parameter space for such systems and show that LRD-like appearances naturally emerge for M ̇ / α ≳ 0.1 M ⊙ yr - 1 , a threshold insensitive to M • , below which the system may transition into classical non-self-gravitating active galactic nucleus (AGN) disks, potentially a later evolution stage. We expect this transition to be accompanied by the enhancement of metallicity and production of dust, giving rise to far-infrared emission. This picture offers a physically motivated and quantitative framework connecting LRDs with AGNs and their associated nuclear stellar population.
SN - 2041-8205
SN - 2041-8213
ER -