Boosting Supermassive Black Hole Growth in the Early Universe by Fuzzy Dark Matter Solitons

Abstract: Observations of massive supermassive black holes (SMBHs) in the early universe challenge existing black hole formation models. We propose that soliton cores in fuzzy dark matter (FDM) offer a potential solution to this timing problem. Our FDM cosmological zoom-in simulations confirm that for a particle mass $m_{\rm FDM}\sim 10^{-22}~{\rm eV}$, solitons are well developed at redshift $z \sim 7$ with masses of $\sim10^9~M_\odot$, comparable to the observed SMBHs. We then demonstrate using hydrodynamic simulations that, compared to cold dark matter, these high-$z$ massive FDM solitons with mass $M_s$ can provide additional gravitational potential to accrete gas and boost the Bondi accretion rate of a growing black hole seed with mass $M_{\rm BH}$ by up to two to four orders of magnitude, in the regime of efficient cooling and negligible radiation pressure. This accretion boosting mechanism is effective for $10^{-22}~{\rm eV} \lesssim m_{\rm FDM} \lesssim 10^{-20}~{\rm eV}$ and potentially beyond as long as $M_s > M_{\rm BH}$. The simulation code GAMER is accessible at https://github.com/gamer-project/gamer.

• The paper demonstrates that fuzzy dark matter (FDM) solitons, simulated with a particle mass of ~10^-22 eV, can boost early supermassive black hole accretion rates by two to four orders of magnitude compared to standard cold dark matter.
• The study uses FDM cosmological zoom-in simulations and hydrodynamic accretion simulations employing a hybrid Schrödinger/Hamilton-Jacobi-Madelung scheme to model soliton formation and their impact on black hole seed growth by redshift z~7.
• This mechanism offers a potential solution to the rapid growth of supermassive black holes observed in the early universe, supporting FDM as a viable dark matter candidate capable of explaining primordial quasar masses.

Analyzing Supermassive Black Hole Growth Enhancement through Fuzzy Dark Matter Solitons

The paper "Boosting Supermassive Black Hole Growth in the Early Universe by Fuzzy Dark Matter Solitons" presents an in-depth exploration of the challenges in explaining the formation of supermassive black holes (SMBHs) at high redshifts, notably around $z \gtrsim 7$. The discovery of these massive entities, which possess masses ranging from $10^7$ to $10^9$ solar masses, poses significant problems for conventional black hole growth models. This study proposes a novel mechanism whereby soliton cores in fuzzy dark matter (FDM) provide the necessary potential to enhance early SMBH accretion rates.

Key Insights and Methodology

The authors conduct FDM cosmological zoom-in simulations, using a particle mass of $m_{\text{FDM}} \sim 10^{-22}$ eV, to demonstrate that solitons can be fully formed by redshift $z \sim 7$. These solitons, with masses comparable to the observed SMBHs, can significantly impact the gravitational potential in their vicinity. Accretion simulations further incorporate hydrodynamic simulations to quantify potential enhancements in the Bondi accretion rate for black hole seeds. The simulations suggest that, given efficient cooling and suppressed radiation pressure, FDM solitons with mass $M_s > \MBH$ can boost accretion rates by two to four orders of magnitude compared to standard cold dark matter models.

The study's methodology revolves around a hybrid scheme employing the Schrödinger and Hamilton-Jacobi-Madelung equations. This methodological innovation allows for high-resolution simulations of the early universe's rapidly forming structures, significantly improving the understanding of SMBH accretion dynamics.

Theoretical and Practical Implications

The proposed mechanism provides a potential solution to the rapid growth problem of early SMBHs, where traditional accretion models fail. By surpassing the conventional Eddington limit, the boosting effect could feasibly account for the mass observed in primordial quasars. Theoretically, this supports FDM as a viable dark matter candidate, addressing issues at cosmic and galactic scales beyond the capabilities of cold dark matter models, particularly in the context of small-scale structure formation.

Practically, if ongoing observational campaigns such as those employing the James Webb Space Telescope further validate the high accretion rates suggested by this study, it could underpin a shift in how astrophysical models incorporate dark matter effects in galaxy formation scenarios. Moreover, the findings provide a framework for understanding the peculiarities of high-redshift environments, dominated by intricate interactions between SMBHs, FDM solitons, and baryonic matter.

Future Developments

The study sets the stage for future exploration into varied scenarios, potentially incorporating additional astrophysical processes such as feedback mechanisms, magnetic fields, and photoionization. It also opens new avenues for observational verification, particularly with instruments sensitive to high-redshift galaxy dynamics and SMBH accretion signatures. Extending the computational models to include more complex interactions under varying cosmological contexts would further refine our understanding of early universe dynamics, offering predictions that can be tested as astronomical technology progresses.

In sum, this paper contributes significantly to a nuanced understanding of early SMBH formation, utilizing the interactions within FDM solitons to extend the predictive capacity of existing cosmological models. As future studies build on these foundations, the integration of FDM into broader astrophysical theory may prove increasingly compelling.