Causal structure of a collapsing thin shell and black hole formation
Presenting author: Diogo L. Silva
An infinitesimally thin shell is a useful tool to study the junction of two different spacetimes. Here we analyze a spherically symmetric collapsing massive thin shell made of dust and separating an interior Minkowski spacetime from an exterior Schwarzschild spacetime. We study the dynamics of the collapse and find the complete description of the trajectory of light rays and the full causal structure of the whole spacetime. The collapsing description is performed in four different exterior coordinate systems, namely, Schwarzschild, Lemaître, Eddington-Finkelstein, and Kruskal. The event horizon can be fully displayed from its appearance at the center of the system up to infinity, and the region of trapped surfaces with its outermost surface, the apparent horizon, can be studied. A collapsing thin shell model mimics in a practical manner a collapsing star and the consequent black hole formation, in much the same way as the Oppenheimer-Snyder collapsing model of 1939, of an interior Friedmann universe joined to an exterior Schwarzschild, and of which we are celebrating 80 years, does. Indeed, both models allow for an understanding of the main relevant features of a real star collapse.
Oral presentation: no. Poster: yes.