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Abstract

Definition and properties of quasi black holes

Objects that are on the verge of being extremal black holes but actually are distinct in many ways are called quasiblack holes. Quasiblack holes are defined here and treated in a unified way through the displaying of their properties. The main ones are (i) their geometry remains perfectly regular everywhere, in spite of the existence of infinite redshifts, (ii) in the limit, outer and inner regions become mutually impenetrable and disjoint, although, in contrast to the usual black holes, this separation is of a dynamical nature, rather than purely causal. It is also shown that quasiblack holes have to be extremal, if we accept only finite surface stresses. If, however, such unbound stresses are allowed, we derived a mass formula for the quasiblack hole that coincides with the mass formula for black holes but is obtained from different physical assumptions.

Differential geometry, general relativity, and unitary theories in the work of Mira Fernandes

Mira Fernandes (1884-1958) was professor at Instituto Superior Técnico (Lisbon) from 1911 to 1953. He worked in a number of mathematical and physics topics, namely, group theory, differential geometry, unitary theories, and classical mechanics, publishing his papers in Italian and Portuguese journals. He has an extended correspondence with Levi-Civita. In unitary theories of the gravitational and electromagnetic fields he published, in Rendiconti della Accademia dei Lincei in the years 1931-1933, one paper in some properties of Schouten's affine connections and another two papers on Straneo's (a mathematical physicist from Genoa) unification scheme

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