Abstract
Large black holes of millions of solar masses are known to be present in the centre of galaxies. Their mass is negligible compared to the mass of the luminous matter, but their entropy far exceeds the entropy of the latter by 10 orders of magnitude. Strong gravitational fields make them 'black' - but at the same time, they cause them to emit radiation so they are not 'dark'. What is the meaning of their borders that may only be crossed once and that leads to the information paradox and what are the properties of their interiors? In discussing these and related questions (is it possible that the volume of a black hole might be infinite?), we uncover the unexpected meaning of the term 'strong gravity'.
Highlights
Black holes (BHs) are sources of the strongest gravitational fields in the Universe
This allows us to estimate that the matter confined within black holes is many orders of magnitude smaller than the luminous matter (LM) in each galaxy, rBH ≤ 10À3rLM
We shall consider that the space outside and inside the horizon is empty—the mass of the black hole is confined at r 1⁄4 0—a singularity
Summary
Black holes (BHs) are sources of the strongest gravitational fields in the Universe. On the other hand, they are the outcomes of these strong gravitational fields. In the centre of Milky Way, there is a BH of mass 4:3∙106M⊙; one of the largest BHs with a mass of a billion solar masses has been found in the centre of the Sombrero galaxy This allows us to estimate that the matter confined within black holes is many orders of magnitude smaller than the luminous matter (LM) in each galaxy, rBH ≤ 10À3rLM (1). Some 20 orders of magnitude smaller than the maximal entropy of our Universe The purpose of this exposition is to illuminate the properties of strong gravitational fields. This will be achieved via a discussion of particular processes and phenomena in the vicinity of the event horizon of black holes, on both sides of this horizon
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