Binary black holes gone MAD: Magnetically arrested minidisks around nonspinning black holes

Abstract

We demonstrate the formation of magnetically arrested minidisks (MAM) around equal-mass, nonspinning binary black holes with magnetohydrodynamic simulations of circumbinary disk accretion in full 3+1 general relativity. The initial separation of $d\sim 30\,M$ allows the black holes to host large minidisks that suppress the total rest-mass accretion rate variability, which is modulated primarily at $\sim 1.6 \, f_{\rm orb}$. Each black hole horizon saturates with dimensionless magnetic flux $\phi \sim 30$. Magnetic reconnection near the horizons drives recurrent eruptions which are expected to drive flaring in the infrared and X-ray bands. Our results establish MAMs as a new outcome of circumbinary disk accretion, and a promising source of novel electromagnetic counterparts to gravitational waves from binary black holes.