The quasi-star model for Little Red Dots: potential and challenges
Abstract
(Abridged) Little Red Dots (LRDs) are a class of sources discovered by JWST observationally defined by a "V-shaped" rest-frame UV-Optical SED, a compact or unresolved morphology, and for having, frequently, broad hydrogen emission lines. Among various models, those involving a quasi-star interpret LRDs as an intermediate stage in the evolution of a super-massive black hole (SMBH) seed into a classic AGN. In this paper, we employ the radiative-transfer code \texttt{Cloudy} to study whether this model is able to reproduce the spectral features commonly observed in LRDs. The model consists of an accreting SMBH (MBH∼105−6 M⊙) surrounded by a convective layer where a black-body (BB) spectrum with T∼5000 K and L∼1044.4 erg s−1 is produced. This BB is then reprocessed by a concentric thick (ΔR∼1000 AU) shell of dense (nH∼1011 cm−3) gas partially ionised by thermal collisions. The emerging radiation is further reprocessed by a diffuse clumpy medium surrounding the quasi-star. We fit this model to JWST/NIRSpec spectra of LRDs from the literature, deriving the main physical parameters and the SMBH masses. Once coupled with the UV emission from a host galaxy, this model is able to reproduce the shape of the UV-to-NIR continuum, including the presence of a Balmer break, as well as the luminosity of the hydrogen emission lines. However, this quasi-star model does not natively account for the presence of broad helium lines and for the possible presence of hot dust, needing additional components to match these observables. Our main result is to show how some LRDs can be modeled as quasi-stars, highlighting that a significant degeneracy exists among different LRD models. This has important consequences for our understanding of the mechanisms driving black hole growth in the early Universe.
Related
- A Spectral Framework for Testing the Quasi-Star Hypothesis in Little Red Dots I: Weighing LRDs by Their Super-Eddington Luminosity Ratios---No Signs of Overmassive Black Holes
- A Cosmological Framework for Stellar Collisions at High Redshift in Proto-globular Clusters, Nuclear Star Clusters, and Little Red Dots
- Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots
- From Feedback-free Star Clusters to Little Red Dots via Compaction
- Towards Self-consistent Modeling of Quasi-Stars and their NLTE Spectra: Implications for Little Red Dots
BibTeX
@misc{gentile2026quasistar,
title = {{The quasi-star model for Little Red Dots: potential and challenges}},
author = {Fabrizio Gentile and Mauro Giavalisco and Emanuele Daddi and David Elbaz and Jean-Baptiste Billand and Maximilen Franco and Benjamin Magnelli and Guillermo Barro and Yingjie Cheng and Nikko J. Cleri and Kelcey Davis and Ivan Delvecchio and Mark Dickinson and Steven L. Finkelstein and Giovanni Gandolfi and Michaela Hirschmann and Weida Hu and Dale Kocevski and Anton M. Koekemoer and Ray Lucas and Sara Mascia and Lorenzo Napolitano and Casey Papovich and Borja Pérez-Díaz and Pablo Perez-Gonzalez and Jonathan R. Trump and Xin Wang and L. Y. Aaron Yung},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.06575},
eprint = {2606.06575},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.06575},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The quasi-star model for Little Red Dots: potential and challenges
AU - Fabrizio Gentile
AU - Mauro Giavalisco
AU - Emanuele Daddi
AU - David Elbaz
AU - Jean-Baptiste Billand
AU - Maximilen Franco
AU - Benjamin Magnelli
AU - Guillermo Barro
AU - Yingjie Cheng
AU - Nikko J. Cleri
AU - Kelcey Davis
AU - Ivan Delvecchio
AU - Mark Dickinson
AU - Steven L. Finkelstein
AU - Giovanni Gandolfi
AU - Michaela Hirschmann
AU - Weida Hu
AU - Dale Kocevski
AU - Anton M. Koekemoer
AU - Ray Lucas
AU - Sara Mascia
AU - Lorenzo Napolitano
AU - Casey Papovich
AU - Borja Pérez-Díaz
AU - Pablo Perez-Gonzalez
AU - Jonathan R. Trump
AU - Xin Wang
AU - L. Y. Aaron Yung
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2606.06575
UR - https://arxiv.org/abs/2606.06575
AB - (Abridged) Little Red Dots (LRDs) are a class of sources discovered by JWST observationally defined by a "V-shaped" rest-frame UV-Optical SED, a compact or unresolved morphology, and for having, frequently, broad hydrogen emission lines. Among various models, those involving a quasi-star interpret LRDs as an intermediate stage in the evolution of a super-massive black hole (SMBH) seed into a classic AGN. In this paper, we employ the radiative-transfer code \texttt{Cloudy} to study whether this model is able to reproduce the spectral features commonly observed in LRDs. The model consists of an accreting SMBH (M_BH∼10^5−6 M_⊙) surrounded by a convective layer where a black-body (BB) spectrum with T∼5000 K and L∼10^44.4 erg s^−1 is produced. This BB is then reprocessed by a concentric thick (ΔR∼1000 AU) shell of dense (n_H∼10^11 cm^−3) gas partially ionised by thermal collisions. The emerging radiation is further reprocessed by a diffuse clumpy medium surrounding the quasi-star. We fit this model to JWST/NIRSpec spectra of LRDs from the literature, deriving the main physical parameters and the SMBH masses. Once coupled with the UV emission from a host galaxy, this model is able to reproduce the shape of the UV-to-NIR continuum, including the presence of a Balmer break, as well as the luminosity of the hydrogen emission lines. However, this quasi-star model does not natively account for the presence of broad helium lines and for the possible presence of hot dust, needing additional components to match these observables. Our main result is to show how some LRDs can be modeled as quasi-stars, highlighting that a significant degeneracy exists among different LRD models. This has important consequences for our understanding of the mechanisms driving black hole growth in the early Universe.
ER -