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AGN & Black Hole Binaries

Manuscript will be submitted soon

When two galaxies merge, their central supermassive black holes sink toward each other and form a gravitationally bound binary. Detecting these binaries before they merge is one of the open challenges in extragalactic astronomy, because their gravitational wave signal is too low-frequency for current detectors and their electromagnetic signatures are ambiguous.

One candidate that attracted enormous attention is the quasar J1430+2303, which showed periodic optical variability that some interpreted as the signature of two black holes orbiting each other with a shrinking period, a system on the verge of coalescence.

Is it a binary - or just a restless disk?
A binary black hole produces a clean, periodic light curve. But an ordinary accretion disk flickers with stochastic "red noise" that can mimic a few cycles of a periodic signal. This ambiguity is exactly what the Tick Tock analysis had to untangle. Flip between the two and see if you could tell them apart.
Tick Tock analysis of J1430+2303
Spectroscopic analysis of J1430+2303 from Saad et al.

In Tick Tock, I investigated this claim using UV-optical spectra from the Hubble Space Telescope and ground-based facilities. The spectral analysis told a different story. The broad emission line profiles, their variability, and the continuum behavior are more naturally explained by changes in the accretion disk itself - not by a binary. My final analysis proposed an alternative explanation, and the manuscript has been submitted for publication.

In a related project on J0950+5128, I participated in line-profile decomposition and accretion disk modeling to understand why some AGN show deviations from the standard thin-disk picture. The goal is to constrain whether binary-induced perturbations leave detectable imprints on the disk kinematics, or whether the variability has a simpler origin.