2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/111138We study Einstein gravity coupled to a massless scalar field in a static spherically symmetric space-time in four dimensions. Black hole solutions exist when the kinetic energy of the scalar field is negative, that is, for a phantom field. These ``scalar black holes'' have an infinite horizon area and zero temperature. They are related through a conformal transformation with similar objects in the Jordan frames of scalar-tensor theories of gravity. The thermodynamical properties of these solutions are discussed. It is proved that any \ssph \bhs with an infinite horizon area have zero Hawking temperature.Latex file, 9 pages, no figure. To appear in the "Prof. José Pl\'ınio Baptista Festschrift"General Relativity and Quantum Cosmologytext