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Energy in Newtonian gravity
Ingemar Bengtsson, Tobias Eklund
In Newtonian gravity it is a moot question whether energy should be localized in the field or inside matter. An argument from relativity suggests a compromise in which the contribu…
The Hawking energy on photon surfaces
Ingemar Bengtsson
The Hawking energy has a monotonicity property under the inverse mean curvature flow on totally umbilic hypersurfaces with constant scalar curvature in Einstein spaces. It grows if…
Black Hole Lattices Under the Microscope
Ingemar Bengtsson, Irina Galstyan
It is known how to choose initial data for Einstein's equations describing an arbitrary number of black holes at a moment of time symmetry. This idea has been used to give insight…
A Toy Penrose Inequality and its Proof
Ingemar Bengtsson, Emma Jakobsson
We formulate and prove a toy version of the Penrose inequality. The formulation mimics the original Penrose inequality in which the scenario is the following: A shell of null dust…
Thermodynamic Metrics and Black Hole Physics
Jan Åman, Ingemar Bengtsson, Narit Pidokrajt
We give a brief survey of thermodynamic metrics, in particular the Hessian of the entropy function, and how they apply to black hole thermodynamics. We then provide a detailed disc…
Black holes: Their large interiors
Ingemar Bengtsson, Emma Jakobsson
Christodoulou and Rovelli have remarked on the large interiors possessed by static black holes. We amplify their remarks, and extend them to the spinning case.
Classics Illustrated: Limits of Spacetimes
Ingemar Bengtsson, Sören Holst, Emma Jakobsson
We carefully study the and limits of the Reissner-Nordström spacetime using Geroch's definition of limits of spacetimes. This is implemented by…
Trapped surfaces in Oppenheimer-Snyder black holes
Ingemar Bengtsson, Emma Jakobsson, José M. M. Senovilla
The Oppenheimer-Snyder solution models a homogeneous round dust cloud collapsing to a black hole. Inside its event horizon there is a region through which trapped surfaces pass. We…
What are extremal Kerr Killing vectors up to?
Jan E. Aman, Ingemar Bengtsson, Helgi F. Runarsson
In the extremal Kerr spacetime the horizon Killing vector field is null on a timelike hypersurface crossing the horizon at a fixed latitude, and spacelike on both sides of the hori…
Some examples of trapped surfaces
Ingemar Bengtsson
We present some simple pen and paper examples of trapped surfaces in order to help visualising this key concept of the theory of gravitational collapse. We collect these examples f…
Trapped surfaces
José M. M. Senovilla
I review the definition and types of (closed) trapped surfaces. Surprising global properties are shown, such as their "clairvoyance" and the possibility that they enter into flat p…
The region with trapped surfaces in spherical symmetry, its core, and their boundaries
Ingemar Bengtsson, José M. M. Senovilla
We consider the region in spacetime containing future-trapped closed surfaces and its boundary $\B$, and derive some of their general properties. We then concentrate…
Where are the trapped surfaces?
Jan E. Aman, Ingemar Bengtsson, José M. M. Senovilla
We discuss the boundary of the spacetime region through each point of which a trapped surface passes, first in some simple soluble examples, and then in the self-similar Vaidya sol…
A Note on trapped Surfaces in the Vaidya Solution
Ingemar Bengtsson, José M. M. Senovilla
The Vaidya solution describes the gravitational collapse of a finite shell of incoherent radiation falling into flat spacetime and giving rise to a Schwarzschild black hole. There…
Anti-de Sitter Quotients: When Are They Black Holes?
Stefan Aminneborg, Ingemar Bengtsson
We point out that the BTZ black holes, and their relatives, can be defined in a cleaner way than they originally were. The covering space can be taken to be anti-de Sitter space, p…
Note on non-metric gravity
Ingemar Bengtsson
We discuss a class of alternative gravity theories that are specific to four dimensions, do not introduce new degrees of freedom, and come with a physical motivation. In particular…
Flat Information Geometries in Black Hole Thermodynamics
J. E. Aman, Ingemar Bengtsson, Narit Pidokrajt
The Hessian of either the entropy or the energy function can be regarded as a metric on a Gibbs surface. For two parameter families of asymptotically flat black holes in arbitrary…
Anti-de Sitter space, squashed and stretched
Ingemar Bengtsson, Patrik Sandin
We study the Lorentzian analogues of the squashed 3-sphere, namely 2+1 dimensional anti-de Sitter space, squashed or stretched along fibres that are either spacelike or timelike. T…
Geometry of black hole thermodynamics
Jan Aman, Ingemar Bengtsson, Narit Pidokrajt
The Hessian of the entropy function can be thought of as a metric tensor on the state space. In the context of thermodynamical fluctuation theory Ruppeiner has argued that the Riem…
Poincare ball embeddings of the optical geometry
M. Abramowicz, I. Bengtsson, V. Karas +1
It is shown that optical geometry of the Reissner-Nordstrom exterior metric can be embedded in a hyperbolic space all the way down to its outer horizon. The adopted embedding proce…
2+1 gravity, chaos and time machines
Ingemar Bengtsson, Johan Braennlund
2+1 gravity for spacetimes with topology RxT^2 has been much studied. We add a description of how to extend these spacetimes across a Cauchy horizon into a region where the torus b…
De Sitter Space and Spatial Topology
Ingemar Bengtsson, Soeren Holst
Morrow-Jones and Witt have shown that generic spatial topologies admit initial data that evolve to locally de Sitter spacetimes under Einstein's equations. We simplify their argume…
Black Holes and Wormholes in 2+1 Dimensions
Dieter Brill
Vacuum Einstein theory in three spacetime dimensions is locally trivial, but admits many solutions that are globally different, particularly if there is a negative cosmological con…
From topological to parametrized field theory
N. Barros e Sa, I. Bengtsson
It has been proposed to study the theory resulting from setting the gravitational constant to zero in the first order formalism for general relativity. In this letter we investigat…