LITTLE RED DOT − HOST GALAXY = BLACK HOLE STAR: A GAS-ENSHROUDED HEART AT THE CENTER OF EVERY LITTLE RED DOT

The central engines of Little Red Dots (LRDs) may be “black hole stars” (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [O III]5008Å line arises exclusively from the host. Using a sample of 98 LRDs (z ≈ 2 − 9) with high quality NIRSpec/PRISM spectra, we demonstrate that the host-subtracted median stack displays a Balmer break > 2× stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED (T_eff ≈ 4050 K, log(L_bol) ≈ 43.9 erg s⁻¹, R_eff ≈ 1300 au). We measure a steep Balmer decrement (Hα/Hβ > 10) and numerous density-sensitive features (e.g., Fe II, He I, O I). These are hallmark signatures of dense gas envelopes, providing population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account for ∼ 20% of the UV emission, ∼ 50% at the Balmer break, and ∼ 90% at wavelengths longer than Hα with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies (M_⋆ ≈ 10⁸ M_⊙) undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [O III]5008Å≈ 1100Å, C III]≈ 12Å), thereby favoring BH* origins linked to star-formation. We show V-shaped LRD selections are biased to high BH*/host fractions (≳ 60% at 5500Å) – less dominant BH*s may be powering JWST’s blue broad-line AGN. We find BH*s are so commonplace and transient (duty cycle ∼ 1%, lifetime ∼ 10 Myrs) that every massive black hole may have once shone as a BH*.