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

Nicolas Sanchis-Gual, Juan Barranco, Juan Carlos Degollado, Darío Nuñez

Abstract

The discovery of supermassive black holes with masses $\gtrsim 10^9 M_\odot$ at redshifts $z\gtrsim 10$ 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 $M_{\rm BH}$, and integrate this rate over cosmological timescales. Our results show that once a critical value of $μM_{\rm BH}$ is reached, scalar field accretion becomes highly efficient, enabling substantial black hole growth even from relatively small initial seed masses. For boson masses $μ\sim 10^{-19}-10^{-16}\,\mathrm{eV}$, black hole seeds of $10^2-10^5 M_\odot$ can reach $10^6-10^8 M_\odot$ within $\sim 10^8$ 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.

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

Abstract

The discovery of supermassive black holes with masses at redshifts 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 and the black hole mass , and integrate this rate over cosmological timescales. Our results show that once a critical value of is reached, scalar field accretion becomes highly efficient, enabling substantial black hole growth even from relatively small initial seed masses. For boson masses , black hole seeds of can reach within 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.

Paper Structure

This paper contains 2 equations, 4 figures, 1 table.

Figures (4)

  • Figure 1: Top panel: Characteristic timescale (e-folding time) in years for different scalar field particle masses $\mu$ as a function of the black hole mass. Bottom panel: ratio $\lambda=|\Gamma|/\Gamma_{\rm Eddington}$ between the scalar field and Eddington accretion rates.
  • Figure 2: Top panel: Black hole mass as a function of the accretion time for $\mu=1.73\times10^{-17}$ eV. Bottom panel: Same for the e-folding time in years.
  • Figure 3: Same as Fig. \ref{['fig2']} for the accretion rate (top panel) and the parameter $\mu M_{\rm BH}$ (bottom panel).
  • Figure 4: Depletion time (solid line) and e-folding time (dashed lines) as a function of the initial black hole seed mass $M^{\rm seed}_{\rm BH}$ for different boson masses $\mu$ and initial boson cloud masses $M_c$. Increasing $M_c$ reduces the total absorption time at fixed $\mu$ by accelerating the early growth of the black hole.