SDSSJ092712.65+294344.0: a candidate massive black hole binary

TL;DR

This paper investigates the quasar SDSSJ092712.65+294344.0 as a potential massive black hole binary, providing estimates of its properties and arguing it is more likely a binary than a recoiling black hole.

Contribution

It presents the first detailed analysis supporting the binary black hole hypothesis for this quasar, including mass estimates and likelihood comparisons.

Findings

Binary hypothesis is 100 times more probable than ejection hypothesis.

Estimated primary black hole mass is ~2 billion solar masses.

Binary has a semi-major axis of 0.34 parsecs and an orbital period of 370 years.

Abstract

In this Letter we explore the hypothesis that the quasar SDSSJ092712.65+294344.0 is hosting a massive black hole binary embedded in a circumbinary disc. The lightest, secondary black hole is active, and gas orbiting around it is responsible for the blue-shifted broad emission lines with velocity off-set of 2650 km/s, relative to the galaxy rest frame. As the tidal interaction of the binary with the outer disc is expected to excavate a gap, the blue-shifted narrow emission lines are consistent with being emitted from the low-density inhomogeneous gas of the hollow region. From the observations we infer a binary mass ratio q ~ 0.3, a mass for the primary of M1 ~ 2 billion Msun and a semi-major axis of 0.34 pc, corresponding to an orbital period of 370 years. We use the results of cosmological merger trees to estimate the likely-hood of observing SDSSJ092712.65+294344.0 as recoiling black hole or as a binary. We find that the binary hypothesis is preferred being one hundred times more probable than the ejection hypothesis. If SDSSJ092712.65+294344.0 hosts a binary, it would be the one closest massive black hole binary system ever discovered.