# Minidisks in Binary Black Hole Accretion

## Abstract

Newtonian simulations have demonstrated that accretion onto binary black holes produces accretion disks around each black hole (“minidisks”), fed by gas streams flowing through the circumbinary cavity from the surrounding circumbinary disk. We study the dynamics and radiation of an individual black hole minidisk using 2D hydrodynamical simulations performed with a new general relativistic version of the moving-mesh code Disco. We introduce a comoving energy variable that enables highly accurate integration of these high Mach number flows. Tidally induced spiral shock waves are excited in the disk and propagate through the innermost stable circular orbit, providing a Reynolds stress that causes efficient accretion by purely hydrodynamic means and producing a radiative signature brighter in hard X-rays than the Novikov–Thorne model. Disk cooling is provided by a local blackbody prescription that allows the disk to evolve self-consistently to a temperature profile where hydrodynamic heating is balanced by radiative cooling. We find that the spiral shock structure is in agreement with the relativistic dispersion relation for tightly wound linear waves. We measure the shock-induced dissipation and find outward angular momentum transport corresponding to an effective alpha parameter of order 0.01. We perform ray-tracing image calculations from the simulations to produce theoretical minidiskmore »

- Authors:

- Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

- Publication Date:

- OSTI Identifier:
- 22663886

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ANGULAR MOMENTUM; BINARY STARS; BLACK HOLES; COMPARATIVE EVALUATIONS; DISPERSION RELATIONS; DISPERSIONS; HARD X RADIATION; HEATING; HYDRODYNAMICS; MACH NUMBER; RADIATIVE COOLING; RELATIVISTIC RANGE; REYNOLDS NUMBER; SHOCK WAVES; SIMULATION; SPECTRA; STARS; STREAMS

### Citation Formats

```
Ryan, Geoffrey, and MacFadyen, Andrew, E-mail: gsr257@nyu.edu.
```*Minidisks in Binary Black Hole Accretion*. United States: N. p., 2017.
Web. doi:10.3847/1538-4357/835/2/199.

```
Ryan, Geoffrey, & MacFadyen, Andrew, E-mail: gsr257@nyu.edu.
```*Minidisks in Binary Black Hole Accretion*. United States. doi:10.3847/1538-4357/835/2/199.

```
Ryan, Geoffrey, and MacFadyen, Andrew, E-mail: gsr257@nyu.edu. Wed .
"Minidisks in Binary Black Hole Accretion". United States.
doi:10.3847/1538-4357/835/2/199.
```

```
@article{osti_22663886,
```

title = {Minidisks in Binary Black Hole Accretion},

author = {Ryan, Geoffrey and MacFadyen, Andrew, E-mail: gsr257@nyu.edu},

abstractNote = {Newtonian simulations have demonstrated that accretion onto binary black holes produces accretion disks around each black hole (“minidisks”), fed by gas streams flowing through the circumbinary cavity from the surrounding circumbinary disk. We study the dynamics and radiation of an individual black hole minidisk using 2D hydrodynamical simulations performed with a new general relativistic version of the moving-mesh code Disco. We introduce a comoving energy variable that enables highly accurate integration of these high Mach number flows. Tidally induced spiral shock waves are excited in the disk and propagate through the innermost stable circular orbit, providing a Reynolds stress that causes efficient accretion by purely hydrodynamic means and producing a radiative signature brighter in hard X-rays than the Novikov–Thorne model. Disk cooling is provided by a local blackbody prescription that allows the disk to evolve self-consistently to a temperature profile where hydrodynamic heating is balanced by radiative cooling. We find that the spiral shock structure is in agreement with the relativistic dispersion relation for tightly wound linear waves. We measure the shock-induced dissipation and find outward angular momentum transport corresponding to an effective alpha parameter of order 0.01. We perform ray-tracing image calculations from the simulations to produce theoretical minidisk spectra and viewing-angle-dependent images for comparison with observations.},

doi = {10.3847/1538-4357/835/2/199},

journal = {Astrophysical Journal},

number = 2,

volume = 835,

place = {United States},

year = {Wed Feb 01 00:00:00 EST 2017},

month = {Wed Feb 01 00:00:00 EST 2017}

}