# Two Problems Only Computers Can Solve -- Gamma Ray Burst Afterglows and Binary Black Hole Accretion

### APA

Ryan, G. (2021). Two Problems Only Computers Can Solve -- Gamma Ray Burst Afterglows and Binary Black Hole Accretion. Perimeter Institute. https://pirsa.org/21090021

### MLA

Ryan, Geoffrey. Two Problems Only Computers Can Solve -- Gamma Ray Burst Afterglows and Binary Black Hole Accretion. Perimeter Institute, Sep. 16, 2021, https://pirsa.org/21090021

### BibTex

@misc{ pirsa_21090021, doi = {10.48660/21090021}, url = {https://pirsa.org/21090021}, author = {Ryan, Geoffrey}, keywords = {Strong Gravity}, language = {en}, title = {Two Problems Only Computers Can Solve -- Gamma Ray Burst Afterglows and Binary Black Hole Accretion}, publisher = {Perimeter Institute}, year = {2021}, month = {sep}, note = {PIRSA:21090021 see, \url{https://pirsa.org}} }

Geoffrey Ryan Perimeter Institute for Theoretical Physics

## Abstract

In the first half of this talk I will discuss recent developments in Gamma Ray Burst (GRB) afterglows. GRBs associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. Viewing GRBs and their afterglows at large inclination can massively affect the observed electromagnetic emission. I will discuss how we model and reason about GRB afterglows in this new era, and new software tools to aid in this work. With our theoretical tools in hand we will briefly go over some recent applications of these models to both short and long GRBs.

In the second half of this talk I will cover ongoing work on binary black hole accretion with the moving-mesh hydrodynamics code Disco. Gas accretion may hinder or accelerate the merger of supermassive binary black holes, affecting predicted rates for LISA and PTA targets. Determining the magnitude and *sign *of the torque exerted on the black hole binary by surrounding gas is a difficult problem that can only be approached by hydrodynamic simulation. I will discuss recent simulations with Disco that explore the dependence of this torque on the mass ratio of the binary and temperature of the gas, the latter of which can reverse the sign of the torque.