A "Black Hole Star" Reveals the Remarkable Gas-Enshrouded Hearts of the Little Red Dots

Rohan P. Naidu, Jorryt Matthee, Harley Katz, Anna de Graaff, Pascal Oesch, Aaron Smith, Jenny E. Greene, Gabriel Brammer, Andrea Weibel, Raphael Hviding, John Chisholm, Ivo Labbé, Robert A. Simcoe, Callum Witten, Hakim Atek, Josephine F. W. Baggen, Sirio Belli, Rachel Bezanson, Leindert A. Boogaard, Sownak Bose, Alba Covelo-Paz, Pratika Dayal, Yoshinobu Fudamoto, Lukas J. Furtak, Emma Giovinazzo, Andy Goulding, Max Gronke, Kasper E. Heintz, Michaela Hirschmann, Garth Illingworth, Akio K. Inoue, Benjamin D. Johnson, Joel Leja, Ecaterina Leonova, Ian McConachie, Michael V. Maseda, Priyamvada Natarajan, Erica Nelson, David J. Setton, Irene Shivaei, David Sobral, Mauro Stefanon, Sandro Tacchella, Sune Toft, Alberto Torralba, Pieter van Dokkum, Arjen van der Wel, Marta Volonteri, Fabian Walter, Bingjie Wang, Darach Watson

First listed 2025-03-20 | Last updated 2025-03-20

Abstract

The physical processes that led to the formation of billion solar mass black holes within the first 700 million years of cosmic time remain a puzzle. Several theoretical scenarios have been proposed to seed and rapidly grow black holes, but direct observations of these mechanisms remain elusive. Here we present a source 660 million years after the Big Bang that displays singular properties: among the largest Hydrogen Balmer breaks reported at any redshift, broad multi-peaked H$β$ emission, and Balmer line absorption in multiple transitions. We model this source as a "black hole star" (BH*) where the Balmer break and absorption features are a result of extremely dense, turbulent gas forming a dust-free "atmosphere" around a supermassive black hole. This source may provide evidence of an early black hole embedded in dense gas -- a theoretical configuration proposed to rapidly grow black holes via super-Eddington accretion. Radiation from the BH* appears to dominate almost all observed light, leaving limited room for contribution from its host galaxy. We demonstrate that the recently discovered "Little Red Dots" (LRDs) with perplexing spectral energy distributions can be explained as BH*s embedded in relatively brighter host galaxies. This source provides evidence that black hole masses in the LRDs may be over-estimated by orders of magnitude -- the BH* is effectively dust-free contrary to the steep dust corrections applied while modeling LRDs, and the physics that gives rise to the complex line shapes and luminosities may deviate from assumptions underlying standard scaling relations.

Short digest

JWST/NIRSpec spectroscopy of the point-like source MoM-BH*-1, observed ~660 Myr after the Big Bang, reveals an enormous Balmer break, broad multi-peaked Hβ, and deep Balmer-line absorption. The authors model it as a “black hole star”: a supermassive black hole enshrouded by extremely dense, turbulent, dust-free gas whose atmosphere imprints the break and absorption while dominating the observed light; narrow [OIII] and residual UV are attributed to a faint host. The data are well matched by a simple Cloudy setup that reproduces the break strength, Balmer EWs, UV faintness, and MIRI continuum, with line ratios consistent with high densities that can collisionally suppress [OIII] and a hint of variability reinforcing the SMBH interpretation. They further argue that Little Red Dots can be explained as BH*s embedded in comparably bright hosts, implying current LRD black hole masses—derived with steep dust corrections and standard scaling relations—may be overestimated by orders of magnitude.

Key figures to inspect

• Figure 1: Inspect the NIRCam/MIRI cutouts and NIRSpec prism+G395M spectra to see the sharp Balmer break causing the red NIRCam colors and the deep, aligned Balmer absorption (e.g., Hγ, Hδ) with broad multi-peaked Hβ; note [OIII]-based systemic redshift and the nearly identical slit positions.
• Figure 2: Compare MoM-BH*-1’s break strength against quiescent and LRD samples using the [3620–3720]Å and [4000–4100]Å windows; confirm it exceeds the dust-free stellar-population maximum, effectively ruling out a stellar-origin continuum.
• Figure 3: Check how the BH* Cloudy model reproduces the smooth Balmer break, Balmer EWs, UV faintness, and MIRI flux with dense, turbulent, dust-free gas; note that narrow [OIII] and extra UV are left to the host and that any excess around H is a modeling artifact from finite Hydrogen levels.
• Figure 4: See the BH*+galaxy superposition that mimics an archetypal LRD (V-shaped SED, complex Hβ profile) and the host-subtraction exercise where the residual resembles a BH*; this visually underpins the claim that LRD BH masses and dust estimates are biased high.
• Extended Data (variability panel): If present, check the reported ~56-day brightening at rest-optical wavelengths as further SMBH evidence and to gauge any short-timescale changes.