Dark-to-black super accretion as a mechanism for early supermassive black hole growth

The discovery of supermassive black holes with masses 10⁹ M_ at redshifts z 10 challenges conventional formation scenarios based on baryonic accretion and mergers within the first few hundred million years. We propose an alternative channel in which ultralight scalar dark matter undergoes dark-to-black conversion via quasi-bound state depletion around black hole seeds. We estimate the accretion rate of the scalar field as a function of the boson mass parameter $μ$ and the black hole mass MBH, and integrate this rate over cosmological timescales. Our results show that once a critical value of μMBH is reached, scalar field accretion becomes highly efficient, enabling substantial black hole growth even from relatively small initial seed masses. For boson masses μ~ 10⁻¹⁹-10⁻¹⁶\,eV, black hole seeds of 10²-10⁵ M_ can reach 10⁶-10⁸ M_ within ~ 10⁸ yr. This dark-to-black mechanism provides a natural pathway for the rapid formation of massive black holes in the early universe, offering a potential probe of the microphysical nature of dark matter.