Neutrino Fast Flavor Conversions in Neutron-Star Postmerger Accretion Disks

• Published in: Physical review letters Vol. 126; no. 25; pp. 1 - 251101
• Main Authors: Li, Xinyu, Siegel, Daniel M.
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 25-06-2021
• Subjects: Abundance; Accretion disks; Black holes; Collapsars; Flavors; Fluid flow; Magnetohydrodynamic simulation; Neutrinos; Neutron stars; Neutrons; Nuclear capture; Nuclear fusion; Outflow; Radiation; Radiation transport; Star mergers
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.126.251101

A compact accretion disk may be formed in the merger of two neutron stars or of a neutron star and a stellar-mass black hole. Outflows from such accretion disks have been identified as a major site of rapid neutron-capture (r-process) nucleosynthesis and as the source of "red" kilonova emissions following the first observed neutron-star merger GW170817. We present long-term general-relativistic radiation magnetohydrodynamic simulations of a typical postmerger accretion disk at initial accretion rates of ˙ M ∼ 1 M⊙ s−1 over 400 ms postmerger. We include neutrino radiation transport that accounts for the effects of neutrino fast flavor conversions dynamically. We find ubiquitous flavor oscillations that result in a significantly more neutron-rich outflow, providing lanthanide and 3rd-peak r-process abundances similar to solar abundances. This provides strong evidence that postmerger accretion disks are a major production site of heavy r-process elements. A similar flavor effect may allow for increased lanthanide production in collapsars.