Image Credit: Asada, K., Nakamura, M., et al. 2014, ApJL, 781, 2
The velocity field of the M87 jet from milli-arcsecond (mas) to arcsecond scales using VLBI observations, and it exhibits a systematic increase from sub-to-superluminal speed in the range from 100 rs to 10^5 rs. The acceleration and
collimation take place simultaneously, which we suggest a characteristic of magnetohydrodynamic
flows.
