Course 8: The Black Hole Environments

Abstract.

Compact objects are astrophysical entities with radii smaller than about 10 Schwarzschild radii. The mass spectrum of these objects ranges from the Chandrasekhar mass of neutron stars to a few solar masses for stellar Black Holes to hundreds of millions of solar masses for supermassive Black Holes in the centers of galaxies. Besides mass, all these objects also carry angular momentum with known spin periods for neutron stars, but unknown spin periods for Black Holes. Black Holes represent exact solutions to Einstein’s equations having a horizon, they are characterized by only two parameters, the mass M and the angular momentum J which is restricted to be $J \le GM^2/c$. Noncollapsed objects dispose however of at least three parameters; in addition to mass and angular momentum, the mass quadrupole moment Q ₂ is not completely arbitrary, but essentially determined by rotation and the equation of state. In the last years, new analytical solutions for rapidly rotating neutron stars have been worked out.

Black Holes in galactic nuclei form now a huge class of compact objects. Jet sources represent an interesting sub-sample of active galaxies. According to the spin paradigm, the rotational energy of the central compact object is the ultimate source of energy for the jet launch. There is some progress in the understanding of large-scale structure of jets in the last years, in particular for sources propagating in a dense cluster environment. In distinction to these macro-jets, the formation of the micro-jets on the parsec-scale is still largely unknown. A magnetic coupling between the rotation of the central object and the out.owing disk plasma is the most probable process. Due to the complexity of modelling this process, we are still not able to present time-dependent simulations proving the evidence for this process. This certainly one of the major challenge of future research in relativistic Astrophysics.

Max Camenzind: This work is partially supported by the Sonderforschungsbereich 439 in Heidelberg, Germany.