Orbit Tomography of Binary Supermassive Black Holes with Very Long Baseline Interferometry

Abstract

Abstract In this work, we study how to infer the orbit of a supermassive black hole binary (SMBHB) by time-dependent measurements with very long baseline interferometry, such as the Event Horizon Telescope (EHT). Assuming a pointlike luminosity image model, we show that with multiple years of observations by EHT, it is possible to recover the SMBHB orbital parameters—eccentricity, (rescaled) semimajor axis, orbital frequency, and orbital angles—from their time-varying visibilities even if the binaries’ orbital periods are a few times longer than the duration of observation. Together with the future gravitational wave detections of resolved sources of SMBHBs with the pulsar timing array, and/or the detections of optical-band light curves, we will be able to further measure the individual mass of the binary, and also determine the Hubble constant if the total mass of the binary is measured through the light curves of the two black holes or measured by alternative methods.