The collapse to a black hole

Now we have a broad view of the Milky Way, we turn back to the stars within the framework of general relativity. The purpose of this chapter is to review some of the astrophysical aspects of stellar black hole formation. When the nuclear fuel is exhausted, stars contract inwards under the influence of their own gravity Our knowledge about the final stages of this collapse suggests that sufficiently massive stars inevitably leave black hole remnants, i.e. regions of spacetime in which gravity is so strong that neither matter nor light can ever escape. We discuss two collapse solutions of the Einstein equations. Whereas the Oppenheimer-Snyder model conveys the principal understanding of the dynamical transition to a (spherically symmetric) non-rotating black hole (collapse time, formation of the event horizon, communication problems of different observers), the parametric collapse of a rotating disk of dust suggests a preference for the extremely rotating (Kerr) black hole and a separation of spacetime domains.