Hunting for Wandering Massive Black Holes

Abstract

We investigate low-density accretion flows onto massive black holes (BHs) with masses of ≳105 orbiting around in the outskirts of their host galaxies, performing 3D hydrodynamical simulations. Those wandering BHs are populated via ejection from the galactic nuclei through multibody BH interactions and gravitational wave recoils associated with galaxy and BH coalescences. We find that when a wandering BH is fed with hot and diffuse plasma with density fluctuations, the mass accretion rate is limited at ∼10%–20% of the canonical Bondi–Hoyle–Littleton rate owing to a wide distribution of inflowing angular momentum. We further calculate radiation spectra from radiatively inefficient accretion flows onto the wandering BH using a semianalytical two-temperature disk model and find that the predicted spectra have a peak at the millimeter band, where the Atacama Large Millimeter/submillimeter Array (ALMA) has the highest sensitivity and spatial resolution. Millimeter observations with ALMA and future facilities such as the next-generation Very Large Array (ngVLA) will enable us to hunt for a population of wandering BHs and push the detectable mass limit down to M • ≃ 2 × 107 for massive nearby ellipticals, e.g., M87, and M • ≃ 105 for the Milky Way. This radiation spectral model, combined with numerical simulations, will be applied to give physical interpretations of off-nuclear BHs detected in dwarf galaxies, which may constrain BH seed formation scenarios.

Interstellar Gas Heating by Primordial Black Holes

“…At high Mach number, the BH accretion rate is expected to be limited to ∼ 10-20% of the canonical Bondi-Hoyle-Lyttleton accretion rate of Eq. (2.1) [66], as shown by recent 3D hydrodynamical simulations. However, the resulting system behavior is sensitive to assumed initial conditions.…”

Unveiling the Population of Wandering Black Holes via Electromagnetic Signatures

“…An important caveat for this work is the underlying assumption of Bondi-like accretion, a sub-grid prescription used in most cosmological simulations. Higher resolution simulations have demonstrated that the accretion rate onto wanderers may be limited to ∼ 10 − 20% the Bondi rate due to the wide distribution of angular momentum encountered moving through the halo (Guo et al 2020). Furthermore, if SMBH accretion rates are low enough for their disks to be in the advection dominated regime, then the accumulation of magnetic flux around their horizons may further suppress accretion rates by orders of magnitude (Igumenshchev & Narayan 2002;Perna et al 2003;Pellegrini 2005;Ressler et al 2021).…”

A Search for Wandering Black Holes in the Milky Way with Gaia and DECaLS

“…It is possible that wandering black holes in more massive halos (e.g., the Virgo Cluster) may encounter sufficient gas to be detected via accretion of intercluster medium (e.g., Guo et al 2020). This detection channel is highly unlikely in Milky Way-mass systems.…”