This textbook introduces the current astrophysical observations of black holes and discusses
the leading techniques to study the strong gravity region around these objects with
electromagnetic radiation. More importantly it provides the basic tools for writing an
astrophysical code and testing the Kerr paradigm. Astrophysical black holes are an ideal
laboratory for testing strong gravity. According to general relativity the spacetime geometry
around these objects should be well described by the Kerr solution. The electromagnetic
radiation emitted by the gas in the inner part of the accretion disk can probe the metric of
the strong gravity region and test the Kerr black hole hypothesis. With exercises and examples
in each chapter as well as calculations and analytical details in the appendix the book is
especially useful to the beginners or graduate students who are familiar with general
relativity while they do not have any background in astronomy or astrophysics.
