On Black Hole Structures in Scalar-Tensor Theories of Gravity
  We review some properties of black hole structures appearing in gravity with a massless scalar field, with both minimal and nonminimal coupling. The main properties of the resulting cold black holes are described. The study of black holes in scalar-gravity systems is extended to $k$-essence theories, and some examples are explicitly worked out. In these cases, even while the existence of horizons is possible, the metric regularity requirement on the horizon implies either a cold black type structure or a singular behavior of the scalar field. 
Kirill A. Bronnikov, J\'ulio C. Fabris, Denis C. Rodrigues
gr-qc astro-ph.HE hep-th