Three Active Black Holes Identified in z=5.02 Galaxy J0148-4214

The finding rests on JWST/NIRSpec integral-field spectroscopy of hydrogen emission lines in J0148-4214. Spectro-astrometry resolved two central sources separated by 620 light-years whose velocity fields cannot be explained by a single rotating disk; a third source 5,500 light-years out shows independent broad-line emission. Masses are estimated at 80 million, 2 million, and 600,000 solar masses, with the smallest exceeding the Eddington limit.

Galaxy mergers were expected to be frequent at z>5, yet simultaneous triple AGN activity supplies direct evidence that dynamical friction and gas inflows can rapidly assemble multiple massive black holes before reionization ends. This configuration is a plausible progenitor for the tight binaries LISA will target and for the over-massive black holes already seen in other z>6 quasars.

No comparable triple-AGN system at z>4 has been confirmed; earlier claims relied on unresolved X-ray or radio data. The current result is limited by the absence of multi-epoch astrometry that could demonstrate orbital motion and by the single sight-line, leaving open whether such triples are common or rare. A statistically meaningful sample from upcoming wide-field IFU surveys will be required.

Future gravitational-wave detections combined with JWST and ELT follow-up can test whether the observed mass ratios and separations match predictions from cosmological simulations that include efficient black-hole seeding.