Research Highlights

Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 6782

(VLBI Observation of Relativistic Jets)

The structure of the M87 jet, from milliarcsecond to arcsecond scales, is extensively investigated, utilizing the images taken with the European VLBI Network, MERLIN, and Very Long Baseline Array. We discover that the jet maintains a parabolic streamline over a range in size scale equal to 10^5 times the Schwarzschild radius. The jet then transitions into a conical shape farther downstream. This suggests that the magnetohydrodynamic jet is initially subjected to the confinement by the external gas which is dominated by the gravitational influence of the supermassive black hole. Afterward the jet then freely expands with a conical shape. This geometrical transition indicates that the origin of the HST-1 complex may be a consequence of the overcollimation of the jet. Our result suggests that when even higher angular resolution is provided by a future submillimeter very long baseline interferometry experiments, we will be able to explore the origin of active galactic nucleus jets and the spin of supermassive black holes.

Distribution of the radius of the M87 jet as a function of the deprojected distance from the core in units of r_s (Schwarzschild radius).

The jet is described by two different shapes. The solid line indicates a parabolic structure with a power-law index a of 1.7, while the dashed line indicates a conical structure with a of 1.0. HST-1 is located around 5 $B!_(B 10^5 r_s. The black area shows the size of the minor axis of the event horizon of the spinning black hole with maximum spin. The gray area indicates the size of the major axis of the event horizon of the spinning black hole with maximum spin, and corresponds to the size of the event horizon of the Schwarzschild black hole. The dotted line indicates the size of the inner stable circular orbit (ISCO) of the accretion disk for the Schwarzschild black hole. (Asada, K. & Nakamura, M., 2012, ApJL, 745, L28)