Black Holes and Neutron Stars in Modified Theories of Gravity

This book provides an up-to-date introduction to (extended) scalar-tensor theories of gravity, from their theoretical motivations to the physics of compact objects in such modifications of general relativity. Key topics include black holes and neutron stars beyond general relativity, spontaneous scalarization, hairy compact objects, and their stability and dynamics. The exposition follows the natural development of the field, beginning with the fundamental ideas and early results that sparked broad interest in the community and progressing toward recent advances. Particular attention is given to nonlinear dynamics, gravitational-wave signatures, and astrophysical constraints on modified gravity. Combining physical insight with derivations of selected key results, the book offers a pedagogical introduction suitable for beginning graduate students and advanced undergraduate students in theoretical physics. It also serves as a useful reference for researchers working in modified gravity, compact objects, gravitational-wave physics, and related areas.