The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets from accretion flows onto black holes involve magnetohydrodynamical (MHD) processes. We have investigated the role of magnetic field in relativistic jets and accretion flows onto black hole via general-relativistic MHD simulations. I found that relativistic jets involving helical magnetic field are unstable via a current-driven kink instability, which leads to helically distorted structure in relativistic jets and dissipates the jet's magnetic energy through magnetic reconnection. I found that an over-pressured relativistic jet leads to the generation of a series of stationary recollimation shocks and rarefaction structures which corresponds to stationary emission components observed in relativistic jets. I also present our new 3D AMR-GRMHD code BHAC and its application to black-hole accretion flows onto a black hole to capture the observational signatures of a black-hole, so-called black hole shadow observed by EHT and future space VLBI.

Yosuke Mizuno obtained a PhD in astrophysics with a thesis on general relativistic magnetohydrodynamic simulations of collapsar as a central engine of gamma-ray bursts. Since April 2004, he was a postdoc at Department of Astronomy, Kyoto University, Japan (2004-05), NASA postdoctoral program fellow at NASA Marshall space flight center, USA (2005-08), research scientist at University of Alabama in Huntsville, USA (2008-11), and assistant research scholar at National Tsing-Hua University, Taiwan (2011-2014). From October 2014, he is a research associate at Institute for Theoretical Physics, Goethe University Frankfurt, Germany. He is a Theory & Simulation Working Group coordinator (2017-present) on Event Horizon Telescope collaboration. He has worked on relativistic astrophysics, black hole astrophysics, plasma astrophysics, and high-energy astrophysics by using numerical simulations. The research object is black hole, active galactic nuclei, gamma-ray bursts, astrophysical jets, and accretion flow. The research area is covered fundamental plasma physics including shocks, instabilities, turbulence, magnetic reconnection and particle acceleration. Recently he has also studied theory of gravity via black hole shadow.