Little Red Dots as Globular Clusters in Formation

John Chisholm, Danielle A. Berg, Michael Boylan-Kolchin, Anna de Graaff, Lukas J. Furtak, Vasily Kokorev, Jorryt Matthee, Julian B. Muñoz, Rohan P. Naidu, Andreas A. C. Sander

First listed 2026-02-17 | Last updated 2026-02-22

Abstract

Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive ($>10^4$ M$_\odot$) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick, continuum-driven winds not fully captured by current models. The LRD $z\sim5-7$ UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at $\log_{10}(M_\ast$/$M_\odot)=5.3$ and an exponential cutoff at high masses, consistent with local globular-cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be $\approx0.3$ Mpc$^{-3}$, similar to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na-O and Al-Mg anti-correlations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe.

Short digest

Proposes Little Red Dots as globular clusters caught in formation, where a very young cluster supplies the rest-UV while a short-lived supermassive star powers the cool, optical modified blackbody that creates the hallmark V-shaped SED. Using the z≈5–7 UV luminosity function and standard evolutionary mass loss, the authors evolve LRDs into a present-day GC mass function with a turnover at log10(M*/Msun)=5.3 and an exponential high-mass cutoff, and infer a total number density ≈0.3 Mpc^-3 consistent with local GCs. The observed LRD redshift window aligns with ages of metal-poor GCs and predicts multiple-population chemistry (He, N enhanced; Na–O and Al–Mg anti-correlations) as a test. A key caveat is that the required temperatures and bolometric luminosities likely demand optically thick, continuum-driven winds not fully captured by current SMS models.

Key figures to inspect

• Figure 1: Inspect the SED decomposition of A2744-45924 to see how a young cluster plus an SMS reproduces the V-shape; note the mismatch near ~3500 Å that points to the need for cooler SMS/wind treatments.
• Figure 2: Check LRDs in the Teff–Lbol plane against SMS tracks and the Hayashi/Eddington lines to gauge the implied radii (~500–2500 au) and near/super-Eddington output, underscoring missing dense-wind physics.
• Figure 3: Follow the transformation from the observed LRD UV LF to the z=0 GC mass function; verify the turnover at log10(M*/Msun)=5.3 and high-mass exponential cutoff against MW and Virgo data.
• Figure 4: Compare LRD redshift distribution to GC age/metallicity bins to see the demographic match to metal-poor GCs and the absence of an obvious metal-rich counterpart.