beecee Posted June 6, 2019 Posted June 6, 2019 https://phys.org/news/2019-06-most-detailed-ever-simulations-black-hole-longstanding.html An international team has constructed the most detailed, highest resolution simulation of a black hole to date. The simulation proves theoretical predictions about the nature of accretion disks—the matter that orbits and eventually falls into a black hole—that have never before been seen. The research will publish on June 5 in the Monthly Notices of the Royal Astronomical Society. Among the findings, the team of computational astrophysicists from Northwestern University, the University of Amsterdam and the University of Oxford found that the inner-most region of an accretion disk aligns with its black hole's equator. This discovery solves a longstanding mystery, originally presented by Nobel Prize-winning physicist John Bardeen and astrophysicist Jacobus Petterson in 1975. At the time, Bardeen and Petterson argued that a spinning black hole would cause the inner region of a tilted accretion disk to align with its black hole's equatorial plane. more at link..... the paper: https://academic.oup.com/mnras/article/487/1/550/5420428 Bardeen–Petterson alignment, jets, and magnetic truncation in GRMHD simulations of tilted thin accretion discs: ABSTRACT: Prevalent around luminous accreting black holes, thin discs are challenging to resolve in numerical simulations. When the disc and black hole angular momentum vectors are misaligned, the challenge becomes extreme, requiring adaptive meshes to follow the disc proper as it moves through the computational grid. With our new high-performance general relativistic magnetohydrodynamic (GRMHD) code H-AMR, we have simulated the thinnest accretion disc to date, of aspect ratio H/R ≈ 0.03 ≈ 1.7°, around a rapidly spinning (a ≈ 0.9) black hole, using a cooling function. Initially tilted at 10°, the disc warps inside ∼5 rg into alignment with the black hole, where rg is the gravitational radius. This is the first demonstration of Bardeen–Petterson alignment in MHD with viscosity self-consistently generated by magnetized turbulence. The disc develops a low-density high-viscosity (αeff ∼ 1.0) magnetic-pressure–dominated inner region at r ≲ 25rg that rapidly empties itself into the black hole. This inner region may, in reality, due to thermal decoupling of ions and electrons, evaporate into a radiatively inefficient accretion flow if, as we propose, the cooling time exceeds the accretion time set by the order unity effective viscosity. We furthermore find the unexpected result that even our very thin disc can sustain large-scale vertical magnetic flux on the black hole, which launches powerful relativistic jets that carry 20−50 per cent20−50 per centof the accretion power along the angular momentum vector of the outer tilted disc, providing a potential explanation for the origin of jets in radio-loud quasars.
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