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Decoding the unknowns: Charging the inner horizons of black holes

رمز گشایی ناشناخته‌ها: شارژ کردن افق‌های درونی سیاه‌چاله‌ها

Black holes are intriguing cosmic objects that have been studied extensively. Their gravitational force is so great that even light can not escape it. Although many studies have predicted the existence of black holes, which have only recently been identified, many questions about these cosmic objects remain unanswered.

Researchers at the University of Leipzig recently Study Vacuum polarization has been investigated using a quantum charged field near the inner horizon of a charged black hole. The results of this study, published in the Journal Physical Review Letters Has been published, showing that on the inner horizon of a black hole, a quantum charged current can be positive or negative.

“The theory of general relativity describes space and time in the sense of unified spacetime, and gravity as the curvature of spacetime,” says Christiane Klein, one of the researchers. One of the most famous predictions of this theory is black holes (areas of space-time from which even light can not escape). If a black hole is electrically charged or rotates, it will have an interesting feature inside: inside the black hole there is a surface whose properties are similar to the characteristics of the event horizon (outer edge) of the black hole. “As a result, they call it the inner horizon.”

Basically, up to the inner horizon of a black hole, space-time, and everything in it can be predicted based on the knowledge available from the universe at a point in the past (which physicists call “primary data”). This ability to predict space-time, known as determinism, is an important feature of physics theories.

A black hole bends the texture of space-time so much that not even light can escape.

However, according to theoretical predictions, the observer who crosses the inner horizon of the dungeon can cross the central singularity of the dungeon (where space and time are infinitely curved) and enter a different world. Moreover, after the inner horizon, determinism theoretically collapses, and as a result the observer’s journey can no longer be determined by the original data.

Roger Penrose, a British mathematician, in his book Gravitational Radiation and Gravitational Collapse predicts that this will not happen because of the remnants of a black hole or other small deviations from the original black space data. will have.

“According to Penrose, these deviations accumulate near the inner horizon and bend space-time so close to the horizon that any observer who approaches it is destroyed and the inner horizon becomes a singularity,” says Klein. This idea is called a strong galactic censorship hypothesis. “So far, different types of black holes with inner horizons and different perturbations of the original data have been studied to test this hypothesis and determine the strength of the singularity on the inner horizon.”

Recent studies have found that in charged black holes that are expanding within a universe, singularity can be weak enough to be traversed. These findings have led some researchers to see what happens if the quantum nature of gravitational fields and matter is taken into account.

“Usually these quantum perturbations are small and negligible,” says Klein. But near the inner horizon, it turned out that quantum effects outweigh the classical effects and are large enough to turn the inner horizon into a strong singularity. “This shows that near the inner horizon of black holes, quantum effects should be avoided, and we decided to take a closer look at quantum effects in this area.”

The inner horizon and event horizon of a black hole
The inner and outer horizons (event) of a black hole

Since an electrically charged black hole can only be made of charged material, Klein and colleagues decided to study specifically quantum charged material. One of the direct visible signs of this type of material is the electric current it produces. As a result, researchers have been trying to determine how this current behaves near the inner horizon of a black hole.

“In previous studies, it has been argued that these currents are mainly due to the random production of particles with opposite charges inside the black hole, which also accelerate in opposite directions,” says Klein. This effect causes the charge of the black hole behind the inner horizon to be discharged. “One of our goals was to check the accuracy of this particle image.”

In a recent paper, researchers considered space-time to represent an expanding universe with a charged black hole. They then incorporated the theory of the quantum field of a fence field into this hypothetical spacetime.

“We temporarily ignored the fact that the quantum field of space-time is changing,” says Klein.

Using their proposed framework, the research team was able to investigate the electric current of a quantum field in the example. They developed their numerical framework based on the results of their previous studies.

Black hole singularity
An imaginary image of the singularity of a black hole

“We have found that the predominant participation of currents in the inner horizon is independent of the state (initial conditions) of the quantum field as long as it is physically reasonable,” says Klein. We selected a suitable case and extracted a formula for flow using space-curvature theory on quantum field theory. “This formula must be evaluated numerically for a set of space-time parameters (mass and charge of a black hole and a cosmic constant that describes the rate of expansion of the universe) and quantum field (mass and charge of the field).”

The key elements of Klein et al.’s formula are called “scattering coefficients”. These coefficients are numbers that describe the extent to which field perturbations are transmitted into a black hole or reflected back into space. Klein et al. Used the methods they had developed in their previous research to calculate these coefficients.

“Flow must always have a sign,” says Klein, “but we found that the predominant contribution of flow to the inner horizon can be positive as well as negative, depending on the parameters of space-time and the quantum field.” It should be noted that in the parametric region very close to the maximum load of the black hole (which, if the load increases, the event horizon will no longer work and the singularity of the center of the black hole Naked The current is always such that it reduces the load on the inner horizon. “This phenomenon ensures that the load never exceeds the maximum allowable.”

The results of the researchers’ analysis were very surprising, as they violated the particle image prediction. Contrary to expectations, the results of these analyzes predicted that under certain conditions, the charge of a black hole inside the inner horizon could be increased by quantum fields.

“Even though our numerical results cannot cover the parameters of spacetime and the realistic quantum field, our work shows that the particle image is not sufficient to fully explain the quantum effects inside black holes,” says Klein.

Image of the black hole of the galaxy Messier 87
Direct image of a black hole cloud at the center of the Messiah Galaxy 87

The results of Klein et al.’s research, in addition to violating particle image predictions, can shed light on findings on the event horizon. In fact, their work shows that quantum effects can behave quite differently from the event horizon near the inner horizon of an event black hole; Where black hole loads are expected to be reduced. In addition, these results could inspire new studies to examine similar quantum effects in more realistic terms.

“We expect realistic black holes to have a small, negligible, but momentarily significant angular (rotational) angle of charge at most once,” says Klein. In fact, charged black holes can be considered merely toy models for rotating black holes: they have many features in common, including the presence of an inner horizon, but charging black holes are mathematically much easier to work with. One of the future directions of our current research is to extend the results to circular black holes. “It will be interesting to see, contrary to current crude belief, whether quantum effects can increase the black hole’s epoch near its inner horizon.”

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