Wednesday, June 28, 2023

Werner Israel theorem (1967): nonrotating black hole must have a spherical horizon

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Let us try to find an intuitive explanation for the theorem of Werner Israel (1967). The theorem states that a nonrotating static black hole...
Monday, June 26, 2023

Merger of two black holes

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Our previous blog post suggests that a Schwarzschild black hole is a perfectly rigid object and its movement has to happen through "fra...
Monday, June 19, 2023

Moving a very heavy neutron star in general relativity

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Suppose that we have a Schwarzschild black hole. We have observers very close to the event horizon. In the Schwarzschild time coordinate, it...
Friday, June 16, 2023

A mass approaches a black hole: where is the horizon?

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Suppose that we have a black hole in the process of an Oppenheimer-Snyder (1939) collapse. The (forming) event horizon is at the distance of...
Sunday, June 11, 2023

Black hole no-hair theorems: an electric charge close to the horizon

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Our previous blog post asked what happens if the collapsing dust ball is not symmetric. Furthermore, what happens if two black holes merge. ...
Saturday, June 3, 2023

The Schwarzschild metric behind the horizon never forms?

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In our blog we have held the view that there cannot exist "infinite" forces. An example of an infinite force is gravity at the hor...
Saturday, May 6, 2023

General relativity has problems defining the kinetic energy in matter lagrangians

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Let us consider the Einstein-Hilbert action once again. It contains the ordinary matter lagrangian density L_M. The ordinary matter lagrangi...