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

article 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 published yes Alberto Torralba Torregrosa author 018f0249-0e87-11f0-b167-cbce08fbd5410000-0001-5586-6950 Jorryt J Matthee author 7439a258-f3c0-11ec-9501-9df22fe067200000-0003-2871-127X Andrea Weibel author Rohan P. Naidu author Yilun Ma author Aidan P. Cloonan author Aayush A Desai author 502cfd30-32c1-11ee-a9a4-d8dad5c6739e Anna De Graaff author Jenny E. Greene author Christian Kragh Jespersen author Ivan Kramarenko author 9a9394cb-3200-11ee-973b-f5ba2a8b16e40000-0001-5346-6048 Sara Mascia author edaf889c-c7cd-11ef-ab1b-bb28c431bd29 Pascal A. Oesch author Wendy Q. Sun author Christina C. Williams author JoMa department IlCa department GradSch department Young galaxies as tracers and agents of cosmic reionization project 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 Teff ≈ 4800 K. The broad Hα 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 (reff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with (formular displayed) kpc, which we interpret as a host galaxy with a stellar mass of ∼10^8 M⊙, in line with the narrow Hα 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. https://research-explorer.ista.ac.at/download/22263/22274/2026_AstrophysicalJourLetters_Torralba.pdf application/pdfno IOP Publishing2026 eng The Astrophysical Journal Letters 2041-8205 2041-8213 2603.2833510.3847/2041-8213/ae7bfd 10052 A. Torralba Torregrosa et al., “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,” The Astrophysical Journal Letters, vol. 1005, no. 2. IOP Publishing, 2026. Torralba Torregrosa A, Matthee JJ, Weibel A, et al. 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. The Astrophysical Journal Letters. 2026;1005(2). doi:<a href="https://doi.org/10.3847/2041-8213/ae7bfd">10.3847/2041-8213/ae7bfd</a> Torralba Torregrosa A, Matthee JJ, Weibel A, Naidu RP, Ma Y, Cloonan AP, Desai AA, De Graaff A, Greene JE, Jespersen CK, Kramarenko I, Mascia S, Oesch PA, Sun WQ, Williams CC. 2026. 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. The Astrophysical Journal Letters. 1005(2), L37. Torralba Torregrosa, Alberto, Jorryt J Matthee, Andrea Weibel, Rohan P. Naidu, Yilun Ma, Aidan P. Cloonan, Aayush A Desai, et al. “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.” The Astrophysical Journal Letters. IOP Publishing, 2026. <a href="https://doi.org/10.3847/2041-8213/ae7bfd">https://doi.org/10.3847/2041-8213/ae7bfd</a>. Torralba Torregrosa, A., Matthee, J. J., Weibel, A., Naidu, R. P., Ma, Y., Cloonan, A. P., … Williams, C. C. (2026). 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. The Astrophysical Journal Letters. IOP Publishing. <a href="https://doi.org/10.3847/2041-8213/ae7bfd">https://doi.org/10.3847/2041-8213/ae7bfd</a> A. Torralba Torregrosa, J.J. Matthee, A. Weibel, R.P. Naidu, Y. Ma, A.P. Cloonan, A.A. Desai, A. De Graaff, J.E. Greene, C.K. Jespersen, I. Kramarenko, S. Mascia, P.A. Oesch, W.Q. Sun, C.C. Williams, The Astrophysical Journal Letters 1005 (2026). Torralba Torregrosa, Alberto, et al. “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.” The Astrophysical Journal Letters, vol. 1005, no. 2, L37, IOP Publishing, 2026, doi:<a href="https://doi.org/10.3847/2041-8213/ae7bfd">10.3847/2041-8213/ae7bfd</a>. 222632026-07-12T22:02:17Z2026-07-13T08:08:41Z