[W84] Scott C. Noble: Investigating the Variability of Accreting Binary Black Holes

Wednesday 25th July 2019, 15.00 UTC

Investigating the Variability of Accreting Binary Black Holes

Scott C. Noble
NASA-GSFC and The University of Tulsa, USA

Alejandro Cárdenas Avendaño


Supermassive binary black holes accreting mass offer a rare
opportunity to probe the strong-field limit of dynamical gravity by
using the ambient gas as a sort of lighthouse. They are important
multi-messenger sources, emitting nHz-mHz gravitational waves (GWs)
and electromagnetic (EM) waves from radio wavelengths to cosmic rays.
Even though such binaries in the GW dominant regime have not been
found yet, prospects for finding them soon are high because they are
bright over a large bandwidth. A key challenge still exists to
distinguish their emission from that of accreting single black holes,
or active galactic nuclei (AGN). Over the past decade of simulating
these sources, using Newtonian and general relativistic codes with
hydrodynamics or magnetohydrodynamics, the community has found that
inhomogeneities or overdensities in the circumbinary disk can modulate
the EM signal with a period related to the binary’s orbital period.
The hope is that this quasi-periodicity may be used, in conjunction
with other evidence, to identify and characterize these systems with
EM waves even before they are found in the GW sector. We will present
our latest general relativistic magnetohydrodynamics simulations of
accreting black hole binaries and show how a binary’s EM and accretion
variability depends on the binary’s mass ratio and separation, and
even on the gas’s thermodynamic properties. Our latest post-process
general relativistic radiative transfer analysis will also be
communicated to demonstrate the importance of using a consistent
thermodynamics-radiation model, and illustrate the roles Doppler
boosting and accretion modulation play in producing a binary’s
variable emission.

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