A direct black-hole mass measurement in a little red dot at high redshift

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad Hα emitters with optically red continua, named little red dots (LRDs)¹, which comprise 15–30% of the high-redshift broad-line AGN population². Owing to their peculiar properties^3,4,5,6, modelling LRDs with standard AGN scenarios has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black-hole masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to two orders of magnitude^{7,https://arxiv.org/abs/2503.16596 (2025)." data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref">8,https://doi.org/10.1038/s41550-026-02813-w (2026)." data-track="click" data-track-action="reference anchor" data-track-label="link" data-test="citation-ref">9,10}. Here we report a direct, dynamical black-hole mass measurement in a strongly lensed LRD at a redshift of 7.04. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million solar masses, consistent with virial black-hole mass estimates. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer M_BH/M_⁎ > 2 (where M_BH is the black-hole mass and M_⁎ is the stellar mass). Such a ‘naked’ black hole, together with its near-pristine environment¹¹, indicates that this LRD is a massive black-hole seed caught in its earliest accretion phase.