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Recent observations of compact astrophysical objects have opened the possibility to probe the nature of gravity in its strong-field regime. Such observations could reveal deviations from general relativity or the standard model. Spontaneous scalarization, which is controlled by scalar-field couplings to gravity, leads to a behavior that resembles a phase transition: the scalar induces measurable effects in the strong-field regime while remaining undetectable in weak-field gravitational experiments. This review presents the spontaneous scalarization mechanism, several scalarization models considered in the literature, and their astrophysical implications for neutron stars and black holes. It also discusses the generalization of such models to other types of fields and instabilities.
Doneva et al. (Thu,) studied this question.