# On the Inner Horizon Instability of Non-Singular Black Holes

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## Abstract

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## 1. Introduction

## 2. Double Null Shell

## 3. Modified Ori Problem

## 4. Discussion and Answer to the Most Common Questions

#### 4.1. What Are the Main Differences between the Two Approaches Described in the Two Sections? Why Are the Results Different?

#### 4.2. Does the Polynomial Growth Imply That the Instability Is Slowed Down?

#### 4.3. Does the Cosmological Constant Play Any Role?

#### 4.4. Is It Reasonable to Consider Only the Late Time Behavior of the Perturbation?

#### 4.5. Analogue Black Holes Seem to Have a Stable Inner Horizon, Why Does This Analysis Not Apply to Them?

#### 4.6. How Is It Possible to Prove the Presence of an Instability without Specifying the Dynamics of the Theory?

#### 4.7. What Are the Main Conclusions of the Analysis?

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Conflicts of Interest

## References

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**Figure 1.**Two null shells cross in a two surface of radius ${r}_{0}$ dividing the spacetime into four regions. We are particularly interested in the situation in which ${r}_{0}$ is very close to the inner horizon.

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**MDPI and ACS Style**

Di Filippo, F.; Carballo-Rubio, R.; Liberati, S.; Pacilio, C.; Visser, M.
On the Inner Horizon Instability of Non-Singular Black Holes. *Universe* **2022**, *8*, 204.
https://doi.org/10.3390/universe8040204

**AMA Style**

Di Filippo F, Carballo-Rubio R, Liberati S, Pacilio C, Visser M.
On the Inner Horizon Instability of Non-Singular Black Holes. *Universe*. 2022; 8(4):204.
https://doi.org/10.3390/universe8040204

**Chicago/Turabian Style**

Di Filippo, Francesco, Raúl Carballo-Rubio, Stefano Liberati, Costantino Pacilio, and Matt Visser.
2022. "On the Inner Horizon Instability of Non-Singular Black Holes" *Universe* 8, no. 4: 204.
https://doi.org/10.3390/universe8040204