Weekly issue

Week 17, 2026

Apr 20–26, 2026

Week 17, 2026 includes 5 curated papers, centered on high-z, LRD, JWST AGN.

2604.22924v1

Supermassive stars with embedded stellar black hole cores: dense assembling star clusters as faint multiple Little Red Dot systems

Antti Rantala

Theme match 4/5

Digest

Direct N-body plus stellar-evolution simulations of assembling clusters with Σ_h ≳ 10^6 M⊙ pc^-2 show that stellar BHs (m_bullet ≲ 60 M⊙) rapidly segregate into the influence radius of collision-grown EMSs/SMSs and become embedded in their envelopes, forming quasi-star–like objects. This QS phase lasts orders of magnitude longer than an SMS lifetime, enabling continued mass growth via stellar collisions and, when multiple BHs are captured, creating embedded gravitational-wave sources. The predicted assembly scales (~100 pc), QS masses (≳10^4 M⊙), and association with nearby blue star-forming clumps align with the faint, multiple-component Little Red Dot population. The work links runaway collisional cluster evolution to early black-hole seed growth consistent with LRD phenomenology.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the five interaction categories A–E and how category E (BH+EMS/SMS) separates in stellar and BH mass—this isolates the embedded-BH regime with extreme star–BH mass ratios.
Figure 2: Trace the six EMS/SMS growth tracks in HD9Z1 vs ID9Z1 (stronger vs weaker winds), noting the collisional rejuvenation that extends lifetimes and the timing of first BH formation relative to when BH–EMS/SMS encounters occur.
Figure 3: Examine BH orbits within the SMS sphere of influence at the quoted Myr snapshot; the near-Keplerian trajectories and BH counts inside r_infl illustrate why capture/embedding becomes likely.
Figure 4: Compare scalar resonant and two-body relaxation timescales inside r_infl with the short Myr interaction window; this shows dynamics can deliver stellar BHs onto interaction orbits quickly enough to form QSs.

Tags

2604.19988v1

Pulsational mass loss from supermassive stars creates the compact shells of Little Red Dots

Devesh Nandal, Igor Chilingarian, Chris Nagele, John Chisholm, Franz E. Bauer, Abraham Loeb

Theme match 4/5

Digest

This paper asks whether late pulsational mass loss from supermassive stars can naturally create the compact dense shells inferred around little red dots. The main result is that the final pre-collapse ejection episode can leave behind an optically thick shell on sub-parsec scales, while earlier episodes expand away and become dynamically unimportant for the observed cocoon. The paper matters because it turns the dense-gas requirement of LRDs into a concrete stellar-evolution prediction rather than an external assumption.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 is the must-see plot: it lays out the full supermassive-star pathway from post-accretion evolution to collapse, and shows why the final pre-collapse ejection is the one relevant for the compact LRD cocoon.
Figure 2 is worth checking next: the left panel shows where the model passes through the Balmer-break/LRD corridor, while the right panel shows that the late, discrete ejection episodes dominate the cumulative mass loss.
Figure 3 is where to test whether the eruptions are physically credible rather than numerical noise, because it compares the episode durations and outflow speeds against pulsation and radiative reference scales.
Figure 4 is the key geometry figure: it shows that the earlier shells expand out and become optically thin, while only the final eruption stays compact and optically important at collapse.

Tags

2604.21666v1

Impact of Primordial Black Hole population on 21 cm observables at high redshift

Atrideb Chatterjee, Barun Maity, Koushiki

Theme match 3/5

Digest

This paper studies how a population of primordial-black-hole-seeded AGN would change high-redshift 21-cm observables. The main result is that the predicted global signal and power spectrum depend strongly on the adopted PBH mass function, but the same models still underproduce the JWST-inferred AGN abundances unless extra sources are added. The paper matters because it links the emerging JWST AGN population to a completely different observational probe and clarifies where PBH scenarios are already under pressure.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 3 is the must-see plot: it shows the global 21-cm signal and power spectrum directly, so this is the bottom-line figure for whether the PBH population leaves an observable imprint.
Figure 1 is worth checking early: it compares the PBH-seeded mass functions against the JWST-inferred abundances and shows the main tension, namely that the model underproduces the observed population by orders of magnitude unless extra AGN sources are added.
Figure 2 explains the physics behind the later 21-cm signals by tracking how the X-ray, Ly-alpha, and ionizing backgrounds change across the PBH scenarios.
Figure 4 is useful for sensitivity: it shows how much the 21-cm prediction moves when the width of the lognormal PBH mass function is changed.

Tags

2604.20966v1

Light, heavy, primordial: exploring the diversity of black hole seeding and growth mechanisms in the JWST era

Pratika Dayal

Theme match 2/5

Digest

Dayal cross-compares astrophysical light (~100 M⊙) and heavy (~10^3–10^5 M⊙) seeds (via DELPHI) with cosmological primordial black holes (10^{0.5–6} M⊙; PHANES) against z≈5–10 observables. The only scenario the data rule out is Eddington-limited accretion onto light seeds; high black hole–to–stellar mass ratios (Mbh/M*≈0.3–1) are achievable with PBHs or heavy seeds under super-Eddington growth. Crucially, only PBHs and Eddington-limited heavy seeds can simultaneously recover the observed Mbh, M*, and extremely low host metallicities (Z≤0.01 Z⊙) at z≈7–10. PBHs also predict a distinctive decline of Mbh/M* with increasing halo mass and occupancy of 10^9–10^11 M⊙ halos, motivating a clustering-based test selecting z≈7 systems with Mbh/M*>0.1 and Lbol≈10^{44–46} erg s⁻¹.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare model BH mass functions across z to see why Eddington-limited light seeds underproduce the high-mass tail relative to JWST-era points, while PBH/heavy-seed tracks match counts at the massive end.
Figure 2: Inspect where bolometric luminosity functions diverge (Lbol≈10^{44–46} erg s⁻¹); this is the regime proposed for selection tests and shows whether PBH or heavy-seed channels can reproduce the bright-end space densities.
Figure 3: Read the Mbh–M* panels by halo-mass color to verify Mbh/M*≈0.3–1 loci and, uniquely for PBHs, the negative trend of Mbh/M* with increasing halo mass at all redshifts.
Figure 4: Use metallicity versus Mbh to check which models reach Z≤0.01 Z⊙ at z≈7–10; compare to Abell2744-QSO1, CANUCS-LRD-z8.6, and GHZ9 points/limits to see the PBH and Eddington-limited heavy-seed agreement.

Tags

2604.19075v1

What is Powering the Enigmatic He II Emitter Hebe: The First Stars or Black Holes?

Junehyoung Jeon, Tae Bong Jeong, Saiyang Zhang, Volker Bromm

Theme match 2/5

Digest

This paper asks whether the He II-bright source Hebe is more naturally powered by first stars or by a black-hole engine. The main result is that the authors favor an extreme Pop III stellar population, while still laying out the heavy-seed black-hole configuration that could mimic some of the same observables. The paper matters because Hebe is one of the cleanest laboratories for separating primordial-star and accreting-black-hole interpretations in the JWST era.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 4 is the must-see comparison plot: it puts the accreting-black-hole SEDs and line predictions next to the Pop III benchmark and the observed He II / H constraints, which is where the two scenarios are most directly confronted.
Figure 1 shows the required LW-flux environment and how rare such halos are, so it is the place to look if you want to judge whether the Pop III pathway is cosmologically plausible.
Figure 2 translates that LW requirement into a Pop III burst mass estimate for Hebe, which is the key bridge between the environmental argument and the observed system.
Figure 3 is the geometry figure for the black-hole scenario, illustrating the configuration in which a heavy seed black hole lives near, but not inside, the main stellar component.