The Evolution and Outflows of Accretion Disks Formed from Compact Object Mergers

Brian Metzger, UC Berkeley

Massive, compact accretion disks are thought to form following the merger of two neutron stars or the merger of a neutron star with a black hole. These hyper-accreting disks may power the relativistic jets that produce short duration gamma-ray bursts (GRBs), an idea that has received recent support due to the localization of some short GRBs in host galaxies with little ongoing star formation. I will discuss calculations of the evolution of viscously-spreading disks produced during compact object mergers, emphasizing important transitions in the disk's thermodynamic properties and their implications for the late-time X-ray activity observed by Swift following some short GRBs. I will also discuss the properties of slower outflows from the disk and their ability to synthesize heavy radioactive elements, the decay of which may power an optical or infrared transient $\sim$ 1 day following the merger. I shall further show that late-time outflows from the disk robustly synthesize neutron-rich isotopes which are rare in our solar system. These calculations can be used to place interesting constraints on the short GRB beaming fraction and the rate of compact object mergers in our galaxy.