A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7
11 affiliations
- 1Institute of Science and Technology Austria (ISTA)
- 2University of Geneva
- 3MIT Kavli Institute for Astrophysics and Space Research
- 4Princeton University
- 5University of Massachusetts
- 6Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138,
- 7Max-Planck-Institut für Astronomie
- 8Cosmic Dawn Center (DAWN)
- 9University of Copenhagen
- 10NSF-DOE Vera C. Rubin Observatory/NSF NOIRLab
- 11University of Arizona
Abstract
Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature T eff ≈ 4800 K. The broad H α emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s −1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data ( r eff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with r eff = 1 . 0 − 0.3 + 0.5 kpc, which we interpret as a host galaxy with a stellar mass of ∼10 8 M ⊙ , in line with the narrow H α emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.
Related
- Origins of the UV Continuum and Balmer Emission Lines in Little Red Dots: Observational Validation of Dense Gas Envelope Models Enshrouding the Active Galactic Nucleus
- An (in)complete NIRSpec census of Balmer absorption in Type 1 AGN – radiation-driven outflows in little red dots, quasars and variable stars
- Gone with the wind? Potential gas inflow in the broad-line region of a QSO at z=0.287 traced by time-varying Balmer absorption
- Balmer Absorption Series and Broad Metal Lines in Two Luminous Little Red Dots
- Signatures of photospheric convection throughout the solar atmosphere: the EVE Sun-as-a-star mHz continuum
BibTeX
@article{torralba2026black,
title = {{A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7}},
author = {Alberto Torralba and Jorryt Matthee and Andrea Weibel and Rohan P. Naidu and Yilun Ma and Aidan P. Cloonan and Aayush Desai and Anna de Graaff and Jenny E. Greene and Christian Kragh Jespersen and Ivan Kramarenko and Sara Mascia and Pascal A. Oesch and Wendy Q. Sun and Christina C. Williams},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = jun,
doi = {10.3847/2041-8213/ae7bfd},
url = {https://doi.org/10.3847/2041-8213/ae7bfd},
note = {CC BY},
}
RIS
TY - JOUR
TI - A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7
AU - Alberto Torralba
AU - Jorryt Matthee
AU - Andrea Weibel
AU - Rohan P. Naidu
AU - Yilun Ma
AU - Aidan P. Cloonan
AU - Aayush Desai
AU - Anna de Graaff
AU - Jenny E. Greene
AU - Christian Kragh Jespersen
AU - Ivan Kramarenko
AU - Sara Mascia
AU - Pascal A. Oesch
AU - Wendy Q. Sun
AU - Christina C. Williams
PY - 2026
DA - 2026/06/30
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/ae7bfd
UR - https://doi.org/10.3847/2041-8213/ae7bfd
AB - Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature T eff ≈ 4800 K. The broad H α emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s −1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data ( r eff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with r eff = 1 . 0 − 0.3 + 0.5 kpc, which we interpret as a host galaxy with a stellar mass of ∼10 8 M ⊙ , in line with the narrow H α emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.
SN - 2041-8205
SN - 2041-8213
ER -