Long Term (250 years) Hydrodynamical Simulation of the Supermassive Black Hole Binary OJ287

TL;DR

This study investigates long-term accretion-driven variability in the candidate SMBH binary OJ287 by performing 3D SPH hydrodynamic simulations with PHANTOM across ~250 years. It compares a canonical high-mass primary with a low-mass secondary, a near-equal-mass setup, and a single-SMBH control to isolate dynamical effects such as spiral density waves, vertical disc perturbations, and orbital precession. The results show that the canonical model produces spiral waves and modest accretion spikes aligned with the 12-year cadence, while the near-equal-mass case disrupts the disc too quickly to match OJ287; radiative transfer is not included, so flux predictions remain indirect. The findings have implications for gravitational-wave searches with pulsar timing arrays and for LSST-era variability studies, providing constraints on system parameters and emphasizing the role of precession in shaping observational signatures.

Abstract

With upcoming facilities capable of detecting photometric and gravitational wave signals from supermassive black hole (SMBH) binaries, studying their long-term accretion-driven variability is timely. OJ287 is a bright, nearby ($z=0.3$), and well-studied candidate for a SMBH binary. As such, it is an excellent case study for how binary dynamics could influence observed active galactic nucleus (AGN) photometric variability. We present 3D hydrodynamic simulations of OJ287, using the code PHANTOM. We simulate two mass ratios: (i) M$_1$ $=$ 1.835$\times$10$^{10}$ M$_\odot$ with M$_2$ $=$ 1.4$\times$10$^{8}$ M$_\odot$, (ii) M$_1\approx$ M$_2$ ($\sim10^{8}$ M$_\odot$) along and (iii) control of a single SMBH and accretion disc. We find that the simulation with masses 1.835$\times$10$^{10}$ M$_\odot$ and 1.4$\times$10$^{8}$ M$_\odot$ evolves consistently with the most currently accepted model of OJ287 as a precessing SMBH binary. The secondary's impacts with the disc result in the formation of spiral density waves and a corresponding $\sim$10-20% increases in the mass accretion rate of the primary SMBH. The impact timings and the mass accretion rate spikes show quasi-periodic variability as a result of the precession of the secondary's orbit with intervals between impacts ranging from $\sim$ 1 year to $\sim$ 10 years. In the near-equal mass case, the disc of the primary becomes tidally disrupted after $\sim$ 2 years. Consequently, the near-equal mass system with a period of 12 years is not a viable candidate for OJ287. This modeling provides insights into the potential signatures of SMBH binaries by both gravitational wave observatories and the Rubin Legacy Survey of Space and Time.

Figures (12)

• Figure 1: A diagram of the geometry of the OJ287 binary black hole system. The secondary SMBH orbits around the primary with a 12 year period. As the secondary passes through the disc of the primary along its orbit (Contact Points), it produces detectable flares.
• Figure 2: The observed optical flux for the OJ287 system from 2005--2022. The wavelength range for this data was $461.5$nm $\leq \lambda \leq 428.6$nm, taken from the MMDC sahakyan2024 catalog. It also contains data from bonning2012. The vertical red lines show when there was a confirmed observed flare from the system. These are 2005.76 valtonen2008, 2007.69 valtonen2008nature, 2015.87 valtonen2016, 2019.36 laine2020 and 2021.9 valtonen2024. Some of these indicate the beginning of the flares.
• Figure 3: Column density snapshots of the three different simulations, in order: A, B and the Control. Simulation A shows disturbance of the disc post impact at 19.2 years, Simulation B shows an almost fully disrupted disc at 2.95 years (the blue dot shows the location of the near-equal mass secondary SMBH) and the Control simulation shows a well-behaved, smooth disc at 57.3 years.
• Figure 4: An illustration of the impact events of the secondary with the disc of the primary. OJ287 is a blazar; its disc is aligned parallel to the observer. During a single orbit of the secondary, one plunge pushes disc material away from us (upper diagram) and the next plunge pushes material away toward us (lower diagram).
• Figure 5: Column density snapshots of Simulation A just before the secondary SMBH (shown as the little black dot) of mass 1.4 $\times$ 10$^8$ M$_\odot$ hits the disc of the primary SMBH of mass 1.835 $\times$ 10$^{10}$ M$_\odot$ in the first panel at 17.2 years. At 17.5 years the secondary has hit the disc producing a point of high density. As the disc rotates a spiral density wave forms, which enables more matter to fall toward the primary SMBH in the following panels. The time from first impact to formation of the spiral is $\sim$ 0.3 years.