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EP: Fachverband Extraterrestrische Physik
EP 15: Astrophysics III
EP 15.3: Vortrag
Freitag, 4. April 2025, 14:15–14:30, ZHG101
Neutrino-cooled accretion disks around massive black holes and their potential as sites for r-process nucleosynthesis — •Javiera Hernández Morales and Daniel M. Siegel — Institute of Physics, University of Greifswald
The astrophysical origin of about half of the elements heavier than iron, synthesized through rapid neutron-capture (the r-process), is still uncertain. Among proposed sites—neutron-star mergers and collapsars—a common scenario is the formation of a black hole surrounded by an accretion disk. A necessary condition for the r-process to occur in outflows from such disks is a neutron-rich environment, which these disks can achieve through neutrino-cooling. However, the minimum rate at which a black hole needs to accrete to activate this mechanism is still an open question. We employ a one-dimensional, general-relativistic model of accretion disks with weak interactions to explore the parameter space of black-hole mass, accretion rate, and α-viscosity, and study the effect of these parameters on the accretion flow and the presence of neutron-rich material. We find that disks with larger accretion rates reach a lower proton fraction Ye, with neutron-rich plasma extending over increasingly wider ranges in radii. We show that the characteristic accretion rates that describe the efficiency of cooling, the opaqueness to neutrinos and the trapping of neutrinos in the accretion flow follow power-law relations with black-hole mass and α-viscosity. Our results suggest that disks around black holes with masses ranging from ∼3M⊙ to ∼103M⊙ could launch neutron-rich outflows and thus be possible sites for the nucleosynthesis of the heaviest elements in the Universe.
Keywords: r-process nucleosynthesis; accretion disks; compact objects; collapsars; black holes