Research Highlights

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Global structure of the M87 jet is examined by multi-frequency observations. Figure shows that distribution of the radius ($r$) of the jet as a function of the de-projected distance ($z$) from the core in units of $r_{\rm s}$: $z \propto r^{a}$. Three data points of mm/sub-mm VLBI cores (at 43, 86, and 230 GHz) are added as the most inner jet emissions at each frequency (Blandford & Konigl 1979). The solid line is the linear least-square for data points except three inner cores (VLBA at 43/86 GHz and EHT at 230 GHz), indicating the parabolic streamline with a power-law index $a$ of $1.73 \pm 0.05$. On the other hand, the dashed line indicates the conical streamline with $a$ of $0.96 \pm 0.1$. HST-1 is located around $5 \times 10^{5}\,r_{\rm s}$, where $r_{\rm s}$ is the Schwarzschild radius. The vertical dashed line indicates the Bondi radius, which is determined by the black hole mass, indicating the jet structural transition occurs beyond the share of the gravitational influence of the supermassive black hole.

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. Expected positions of VLBI cores at 340 GHz and 690 GHz by future sub-mm observations are also plotted. Thus, our GLT project will seek the innermost part of the relativistic jet in M87, where the jet is launched, at a few $r_{\rm s}$ scale (Asada, K & Nakamura, M., 2012, ApJ, 745, L28; Nakamura, M. & Asada, K., 2013, ApJ, 775, 118).