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Protostars grow through gas accretion from the surrounding disk. In the early protostellar evolution, the disk extends down to the protostellar surface, forming a narrow layer in which the angular velocity of the accreting gas adjusts to the rotational speed of the protostar. This accretion mode is called boundary layer accretion. The mass and angular momentum transfer in boundary layer accretion, an expected accretion mode in the early protostellar evolution, has been poorly understood. To reveal the process, we present and analyze results of a global, three-dimensional magnetohydrodynamic model of boundary layer accretion around a strongly magnetized, convective protostar. The simulation found a new accretion mode which is involved with stellar magnetic fields. Our findings could provide a solution to a long-standing problem about the angular momentum transfer mechanism in the boundary layer. We also discuss some observational implications such as the protostellar luminosity problem.
F608
Since the invention of the laser in 1960, lasers have been applied as a tool for research in our surroundings and in advanced technology and basic science. Today, I will give talks on the following two physics topics in our research field. Finally, I would like to describe a project for which an open call has been launched. 1. Study of astrophysical plasmas by intense laser 2. Research on laser fusion using the world's largest NIF facility 3. Formation of an interdisciplinary research group for the fusion energy project. (Full text here)
F608
Accretion disk winds in compact objects in X-ray binaries, suggested by the blue-shifted absorption lines in spectroscopic data, are important phenomena to address the understanding of the physics of AGN feedback. Those objects show strong X-ray radiation from the accretion flows and clear absorption/emission lines of winds without contamination from stellar components and dust extinction of interstellar medium. However, the driving mechanisms of the winds are unclear. To tackle this, we build a comprehensive model for X-ray spectra. The detail line profiles are simulated by Monte-Carlo radiation transfer, whose input density/velocity fields are calculated by the radiation hydrodynamics code. Our models show that the observed spectra are well described by the winds launched at a larger radius driven by radiative heating/acceleration, where the mass/momentum/energy transfer to outer systems is calculable by the observed SED, luminosity, and the disk size. This motivates us to make quantitative models of AGN feedback for galaxy formation by radiative (accelerated/heated) winds determined by fundamental parameters related to black holes, such as mass and accretion rate.
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Ultraluminous X-ray sources (ULXs) are bright, point-like, off-nuclear X-ray sources. Their X-ray luminosity exceeds the Eddington luminosity for the stellar mass black hole, and the energy production mechanism remains a great mystery. We have performed general relativistic radiation magnetohydrodynamics simulations of super-Eddington accretion flows onto neutron stars with dipole and quadrupole magnetic fields, as modeling the neutron-star-powered ULXs. In our simulations, accretion disk, accretion flows along the neutron star’s magnetic field, and optically thick outflows driven by the strong radiation force appear. Such outflows can explain the thermal emission with a temperature of 1E+7 K and a blackbody radius of ~100 km detected in ULX. In this talk, the magnetic field structure (strength and configuration) of the neutron star in the ULXs is also discussed.