JWST's Little Red Dots as collapsed Supermassive Dark Stars

Abstract: The nature of the ``Little Red Dots'' (LRDs) is one of the most profound mysteries posed by the JWST data. One promising class of models that can reproduce the observed LRDs spectra and morphology are quasi-stars: massive envelopes surrounding accreting black holes formed via the collapse of supermassive stars (SMSs). However, the canonical SMS pathway relies on a highly restricted set of environmental and structural conditions: strong Lyman--Werner (LW) backgrounds to suppress H$2$ cooling, high and sustained gas inflow rates to enforce entropy stratified envelopes, and assume non-zero rotational support in order to prevent GR instability collapse before $\sim 10^6 M{\odot}$. Here we show that supermassive dark stars (SMDSs), powered by dark matter (DM) annihilation rather than nuclear burning, naturally satisfy the key structural and energetic requirements for quasi-star (QS) formation while relaxing {\it all} of those restrictive conditions listed above. Moreover, quasi-stars formed through the SMDS pathway are born with prompt BH masses ($\gtrsim 10\%$) of the progenitor mass. They therefore enter directly into a late-stage quasi-star regime; subsequently the envelope expands and cools until its photosphere reaches the zero-metallicity opacity limit $(T_{\rm eff}\sim3000$-$6000\,{\rm K}$). Those cool, optically thick, unresolved photospheres can reproduce key features of many JWST LRDs.

• The paper presents a model where collapsed dark stars powered by dark matter annihilation trigger prompt ~10^6 M☉ black hole formation and luminous, weakly bound envelopes matching JWST observations.
• It employs detailed MESA modeling to quantify the GR instability onset, envelope binding energy, and the transition to inflated quasistar states.
• The SMDS pathway circumvents extreme accretion and environmental constraints, offering a robust alternative mechanism for early supermassive black hole seed formation.

Supermassive Dark Stars as Progenitors of JWST’s Little Red Dots: Collapse, Quasi-star Formation, and Observational Implications

Overview and Motivation

This paper rigorously addresses the enigmatic “Little Red Dots” (LRDs) detected at $z \gtrsim 7$ by JWST, whose SEDs, luminosities, and morphologies challenge conventional interpretations based on stellar populations or AGN accretion phenomena. The study systematically explores the hypothesis that collapsed supermassive dark stars (SMDSs), powered by DM annihilation rather than nuclear fusion, offer an energetically and structurally consistent progenitor pathway for quasi-star-like remnants capable of reproducing LRD observables. This analysis provides a technical comparison to canonical quasi-star formation via supermassive stars (SMSs) and quantifies the advantages introduced in the SMDS-driven scenario.

Stellar Collapse and Structural Properties

The study utilizes detailed MESA modeling to track SMDS evolution powered by 100 GeV WIMP annihilation, identifying the onset of Feynman–Chandrasekhar GR instability at $M_\star \approx 2.6 \times 10^6\,M_\odot$ and $R_\star \approx 1.7 \times 10^4\,R_\odot$, with $T_{\rm eff} \approx 2.6 \times 10^4\,$K and $$L \approx L_{\rm Edd}(M_\star) \approx 10^{11}\,L_\odot$$. The internal structure is radiation-pressure dominated, convective, and closely approximated by $n = 3$ polytropic behavior. The paper analytically and numerically verifies that the SMDS sequence crosses the GR-stability threshold, confirming the collapse endpoint.

Unlike SMSs, which require fine-tuned environmental parameters—such as strong LW backgrounds to suppress H$_2$ cooling, rapid baryonic accretion, and rotational support—the SMDS route naturally achieves these conditions via DM heating. This allows for massive, extended envelopes to persist at modest baryonic accretion rates, obviating the need for extreme inflow rates and specialized halo environments.

Prompt BH Formation and Envelope Survival

A salient result of this analysis is the demonstration that SMDS collapse produces a prompt BH mass $M_{\rm BH,0} \sim 10^6\,M_\odot$, representing $\gtrsim 0.5$ of the progenitor mass—a stark departure from canonical SMS quasi-stars where $M_{\rm BH,0}/M_\star \lesssim 0.01$. The study quantifies the binding energy of the remaining envelope ($M_\star \approx 2.6 \times 10^6\,M_\odot$0erg) and calculates the energetics of collapse ($M_\star \approx 2.6 \times 10^6\,M_\odot$1erg for typical coupling parameters), finding that survival and subsequent inflation of the envelope are robustly achievable for plausible feedback and deposition efficiencies.

The envelope’s weak binding, a direct consequence of distributed DM heating, facilitates inflation to quasi-star radii ($M_\star \approx 2.6 \times 10^6\,M_\odot$2 for $M_\star \approx 2.6 \times 10^6\,M_\odot$3~K), requiring a moderate energy input relative to pre-collapse conditions. Time-integrated accretion feedback during the quasi-star phase, combined with collapse-generated heating, provides sufficient energy on rapid timescales ($M_\star \approx 2.6 \times 10^6\,M_\odot$4~yr) to reach the required large radii and effective temperatures.

Quasi-star Formation: Comparative Pathways

The paper offers a systematic comparison between SMS-based and SMDS-based quasi-star formation. Key findings are:

• Environmental Robustness: SMDS formation is not restricted to atomically cooled halos or extreme LW backgrounds; it operates over a broader range of early-universe environments.
• Accretion Rates: SMDSs reach $M_\star \approx 2.6 \times 10^6\,M_\odot$5 at $M_\star \approx 2.6 \times 10^6\,M_\odot$6, whereas SMSs require $M_\star \approx 2.6 \times 10^6\,M_\odot$7 to avoid fragmentation.
• Envelope Structure: SMDS envelopes are convective and weakly bound, favoring inflation and quasi-star formation; SMS envelopes require hylotropic stratification.
• BH-to-envelope Ratio: The SMDS channel enables $M_\star \approx 2.6 \times 10^6\,M_\odot$8, realizing late-stage quasi-star regimes immediately post-collapse.

Recent saturated-convection quasi-star models [Coughlin_Begelman_2024] demonstrate stability for envelopes at large BH fractions ($M_\star \approx 2.6 \times 10^6\,M_\odot$9), supporting the physical plausibility of these late-stage remnants.

Observational Connections: JWST Little Red Dots

The quasi-star-like remnants from SMDS collapse match LRD observables with $R_\star \approx 1.7 \times 10^4\,R_\odot$0--$R_\star \approx 1.7 \times 10^4\,R_\odot$1, $R_\star \approx 1.7 \times 10^4\,R_\odot$2--$R_\star \approx 1.7 \times 10^4\,R_\odot$3~K, and compact, unresolved morphologies. The required envelope inflation is energetically favored, and the resulting surface mass density guarantees deep Compton thickness ($R_\star \approx 1.7 \times 10^4\,R_\odot$4--$R_\star \approx 1.7 \times 10^4\,R_\odot$5), efficiently obscuring the central BH and reproducing the red colors and SED shapes seen in JWST LRDs. The inflation factor ($R_\star \approx 1.7 \times 10^4\,R_\odot$6) from SMDS birth to quasi-star state is markedly less stringent than SMS channels ($R_\star \approx 1.7 \times 10^4\,R_\odot$7--$R_\star \approx 1.7 \times 10^4\,R_\odot$8).

SMDS remnants also provide seeds for early supermassive BHs, consistent with the existence of luminous high-$R_\star \approx 1.7 \times 10^4\,R_\odot$9 quasars and potentially contributing to GW backgrounds from SMBH mergers [ghodla2025reconstructingptameasurementsearly].

Theoretical and Practical Implications

The SMDS pathway circumvents the environmental and structural bottlenecks of SMS-based quasi-star formation, and the energetic analysis confirms envelope survival and observability. This supports a physically viable mechanism for producing both unresolved luminous LRD components and massive BH seeds in the early universe. The theoretical implications extend to DM–stellar interactions and the rapid emergence of massive BHs without the canonical requirements for extreme inflow or rotation. Practically, this scenario strengthens the interpretation of JWST LRDs as late-stage quasi-stars and motivates future modeling via GR-hydrodynamics and radiative transfer calculations for direct comparison with JWST spectroscopy.

Conclusion

This paper demonstrates that supermassive dark stars, powered by DM annihilation, are compelling progenitors for late-stage quasi-star-like remnants consistent with JWST’s Little Red Dots. By removing the environmental and structural fine-tuning required in the SMS pathway and enabling large BH-to-envelope mass fractions and weak envelope binding, the SMDS route provides robust theoretical foundations for the LRD phenomenon and early SMBH formation. Future work should integrate multi-dimensional collapse, feedback, and radiative transfer studies to refine and validate this model in the context of JWST observations and early-universe cosmology.

(2606.02539)