Astronomers used a detailed cosmic simulation to show how “overmassive” black-hole galaxies at redshift about 10 can form naturally from very large black hole seeds. These galaxies, found by the James Webb Space Telescope, host black holes that are much heavier compared with their stars than in nearby galaxies. In the simulation a direct-collapse black hole (DCBH) of about 70,000 solar masses, born at redshift z = 25.7, grows to about 6.0 × 10^6 solar masses by z = 10.1 while its galaxy reaches roughly 4 × 10^8 solar masses in stars. The resulting black-hole to stellar mass ratio (MBH/M*) of order 0.01 matches objects such as GN-z11, UHZ1 and GHZ9 observed near z ≃ 10.

The team ran the first cosmological calculation that follows a DCBH and its host galaxy together for several hundred million years while resolving star formation in tiny early halos. They used the ENZO code with adaptive mesh refinement and included gas chemistry, X-ray and ultraviolet radiation, and supernova feedback from both Population III (first-generation) and later Population II stars. The simulation had dark matter particles of about 3,600 solar masses and a smallest cell size of 4 parsecs, which the authors say is fine enough to resolve star formation in the smallest early halos and the Bondi radius (a measure used to estimate gas capture) for a 10^5‑solar-mass black hole.

The key physical story in the run is a two-stage effect. Early on the black hole’s X-rays heat gas near it and delay star formation for roughly ten million years. That suppression lets the black hole grow without being swamped by local star formation. Later, brief but powerful explosions from massive Population III stars (pair-instability supernovae) blast metals far from the center. Those events make star formation bursty and then, once metals build up above a tiny threshold (about 10^−4 times the Sun’s metal fraction), continuous Population II star formation begins. That sequence — early suppression of stars followed by later metal-driven starbursts — produces the high black-hole to stellar mass ratios seen in observed overmassive black-hole galaxies.