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Updated: May 29, 2026

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
Published on: February 4, 2017
A direct black-hole mass measurement in a little red dot at high redshift
Ignas Juodžbalis1,2, Cosimo Marconcini3,4, Francesco D'Eugenio5,6
1Kavli Institute for Cosmology, University of Cambridge, Cambridge, UK. ij284@cam.ac.uk.
Abstract:
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 properties3-6, 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 magnitude7-10. 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 MBH/M⁎ > 2 (where MBH 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.
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