Black hole interior structure
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Black Hole Interior Structure: Key Features and Models
Mass Inflation and Inner Horizons in Rotating and Charged Black Holes
The interior of rotating and charged black holes is marked by complex dynamics near the inner (Cauchy) horizon. In rotating black holes, hyper-relativistic counter-streaming between ingoing and outgoing streams leads to a phenomenon called mass inflation, where the internal mass parameter grows rapidly, followed by a collapse at extremely small radii. This process is described by fully nonlinear, dynamical solutions that are conformally stationary and axisymmetric, but these solutions break down when rotational motion becomes significant compared to radial motion at tiny scales . For slowly rotating, steadily accreting charged black holes, mass inflation occurs only in the radial direction, and angular motion has a negligible effect on the overall structure for small accretion rates .
In charged black holes, models suggest that the interior can be described by matching a de Sitter core to the external Reissner–Nordström solution at a thin transition layer near the Cauchy horizon, or by considering evaporation through non-stationary null shells 23. In some higher-dimensional charged helical black holes, the inner Cauchy horizon is absent, and the interior evolves toward a stable Kasner-type singularity .
Symmetries, Regularization, and Quantum Aspects
Recent research has uncovered new symmetries in the black hole interior, specifically a Poincaré algebra of conserved charges that governs the dynamics inside the event horizon. This symmetry, related to the BMS group, provides a framework for distinguishing between different regularization and quantization schemes. Using techniques from loop quantum cosmology, it is possible to regularize the singularity and describe a transition from a black hole to a white hole, preserving these symmetries in the process . This approach opens new avenues for understanding the quantum structure of black hole interiors.
Regular and Exotic Core Models
Some models propose that the black hole interior can be regular, avoiding singularities. For example, one scenario suggests a core made of a condensate of Higgs and Z bosons, with negative pressure balancing gravitational collapse. The size of this core depends on the black hole's mass and charge, and in nearly extremal cases, the core can fill the entire interior, potentially preventing singularity formation . Another model describes the interior as an ideal fluid with negative pressure, requiring a specific range for the equation of state parameter to maintain a solution .
Oscillatory and Bouncing Dynamics
In certain black hole solutions, especially those involving scalar fields or helical deformations, the interior evolution is characterized by oscillatory or bouncing behavior. For instance, in AdS black holes coupled to scalar fields, the interior undergoes an infinite sequence of Kasner epochs, with the scalar field driving repeated "bounces" before the geometry ultimately approaches a Schwarzschild-like singularity . Similarly, in five-dimensional helical black holes, oscillations in the metric field occur near the horizon, and the interior evolves toward a stable Kasner singularity .
Schwarzschild Black Hole Interior and Open Questions
The classic Schwarzschild solution remains a cornerstone for understanding black hole interiors, but significant ambiguities and conceptual challenges persist, especially when considering the viewpoint of an observer inside the event horizon. Analyses of the interior metric, conserved quantities, and coordinate systems reveal that the true structure of realistic black hole interiors is still not fully determined and remains a subject of ongoing debate .
Conclusion
The study of black hole interior structure reveals a rich landscape of physical phenomena, including mass inflation, symmetry-driven regularization, exotic core models, and oscillatory dynamics. While significant progress has been made in modeling both classical and quantum aspects, the true nature of black hole interiors—especially the resolution of singularities and the role of quantum gravity—remains an open and active area of research 12345678+2 MORE.
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