Viscous evolution of a massive disk surrounding stellar-mass black holes in full general relativity

Long-term viscous neutrino-radiation hydrodynamics simulations in full general relativity are performed for a massive disk surrounding spinning stellar-mass black holes with mass M_BH=4 , 6, and 10 M_⊙ and initial dimensionless spin χ ≈0.8 . The initial disk is chosen to have mass M_disk≈0.1 or 3 M_⊙ as plausible models of the remnants for the merger of black hole-neutron star binaries or the stellar core collapse from a rapidly rotating progenitor, respectively. For M_disk≈0.1 M_⊙ with the outer disk edge initially located at r_out∼200 km , we find that 15%-20% of M_disk is ejected and the average electron fraction of the ejecta is ⟨Y_e⟩=0.30 - 0.35 as found in the previous study. For M_disk≈3 M_⊙, we find that approximately 10 %- 20 % of M_disk is ejected for r_out≈200 - 1000 km . In addition, the average electron fraction of the ejecta can be enhanced to ⟨Y_e⟩≳0.4 because the electron fraction is increased significantly during the long-term viscous expansion of the disk with high neutrino luminosity until the mass ejection sets in. Our results suggest that not heavy r -process elements but light trans-iron elements would be synthesized in the matter ejected from a massive torus surrounding stellar-mass black holes. We also find that the outcomes of the viscous evolution for the high-mass disk case is composed of a rapidly spinning black hole surrounded by a torus with a narrow funnel, which appears to be suitable for generating gamma-ray bursts.