Binary black hole accretion during inspiral and merger

Abstract

We present the results of 2D, moving mesh, viscous hydrodynamical simulations of accretion onto merging supermassive black hole (SMBH) binaries. We include viscous heating, shock heating, and radiative cooling, and simulate the transition from the "pre-decoupling" epoch, where the inspiral timescale is longer than the viscous timescale, to the "post-decoupling" epoch, where the inspiral timescale is shorter than the viscous timescale. We find that there is no abrupt halt to the accretion at decoupling, but rather the accretion shows a slow decay, with significant accretion well after the expected decoupling. Moreover, we find that the luminosity in X-rays is significantly higher prior to the merger, as orbital energy from the SMBH binary is converted to heat via strong shocks inside the cavity, and radiated away. Following the merger, the cavity refills viscously and the accretion rate relaxes to the Shakura-Sunyaev value, while the X-ray luminosity drops as the shocks quickly dissipate.

Multiple periods in the variability of the supermassive black hole binary candidate quasar PG1302-102?

“…D 'Orazio et al (2015) showed that, under the assumption that the optical period corresponds to the longer period of the hotspot in the accretion disk, PG1302 would be in the gravitational inspiral regime. This would confirm that SMBHBs can produce bright electromagnetic emission even at these late stages of the merger (Noble et al 2012;Farris et al 2015).…”

Relativistic Dynamics and Mass Exchange in Binary Black Hole Mini-disks

“…In contrast, recent Newtonian simulations (see, e.g. (Farris et al 2014;Muñoz & Lai 2016)) have clearly demonstrated that individual "mini-disks" form around each BH over many binary orbital periods.…”

“…However, a few years ago multi-dimensional numerical simulations of circumbinary disks with internal stresses showed that streams of gas are, in fact, readily peeled off the inner edges of such disks (MacFadyen & Milosavljević 2008;Shi et al 2012;Noble et al 2012;D'Orazio et al 2013). More recently, simulations with carefully defined external accretion rates have shown that essentially all the mass passing through the circumbinary disk is conveyed to the binary (Farris et al 2014;Shi & Krolik 2015). Shi & Krolik (2015) showed in detail how binary torques acting on streams in the gap can drive gas back out to the circumbinary disk, where a portion of the streams' mass loses enough of its angular momentum by shock deflection that it then falls directly to the binary.…”

A reduced orbital period for the supermassive black hole binary candidate in the quasar PG 1302-102?

“…Recent simulations (Noble et al 2012;Farris et al 2015a) show that high levels of accretion can persist well past the decoupling phase, delivering gas to the binary efficiently until much closer to coalescence. These simulations also exhibit the lopsided cavity which generates the χt bin variability considered here.…”