Physical black holes in fourth-order gravity

Understand

The existence of black holes is a central prediction of general relativity and thus serves as a basic consistency test for modified theories of gravity.

• In spherical symmetry, only two classes of dynamic solutions are compatible with the formation of an apparent horizon in finite time of a distant observer.
• Moreover, the formation of black holes follows a unique scenario involving both types of solutions.
• To be compatible with their existence, any self-consistent theory of modified gravity must satisfy several constraints.