Nakamura, M., Asada, K.: The parabolic jet structure in M87 as a magnetohydrodynamic nozzle. ApJ 775, 118 (2013). arXiv:1308.1436 Narayan, R., Yi, I., Mahadevan, R.: Explaining the spectrum of Sagittarius A∗ with a model of an accreting black hole. Nature 374, 623–625 (1995...