String Theory Reveals Black Holes as Bound States of Strings.

Research demonstrates that, at sufficiently small string coupling, a black hole transforms into a bound state of self-gravitating fundamental strings, described by winding strings around a time circle, analogous to the Horowitz-Polchinski solution. Analysis within dilaton and RST models reveals associated background radiation mirroring Hartle-Hawking behaviour.
The nature of black holes and their potential composition remains a central question in theoretical physics, with recent investigations suggesting they may not be singular points, but rather complex configurations of fundamental strings. These strings, one-dimensional extended objects, are theorised to bind together through self-gravitation, forming a stable, non-singular alternative to the traditional black hole. Akihiro Ishibashi, Yoshinori Matsuo, and Akane Tanaka, researchers from Nagoya University and Kindai University, explore this possibility in their paper, “Self-gravitating strings and quantum effects in two-dimensional gravity”. They present analytical solutions describing these winding strings within the framework of two-dimensional dilaton theories, specifically examining the geometry and quantum effects surrounding these configurations, and drawing parallels between their behaviour and the Hartle-Hawking vacuum state near a black hole’s event horizon. Their work utilises the RST model, a specific instance of two-dimensional gravity, to investigate background radiation emitted by these string configurations.

Theoretical physicists are investigating the final stages of black hole evaporation, proposing a resolution to the long-standing information paradox. This paradox arises because quantum mechanics dictates information cannot be destroyed, yet black holes, according to classical general relativity, appear to obliterate anything that falls within their event horizon. Researchers analyse self-gravitating fundamental strings, demonstrating they represent a stable endpoint for black hole evaporation and potentially preserve information lost during the process. This work builds upon existing frameworks in string theory and black hole physics, offering a concrete model for the ultimate fate of these enigmatic cosmic objects and providing analytical tools for further investigation.

The study centres on analysing winding strings—strings wrapped around a Euclidean time circle—initially proposed by Horowitz and Polchinski, within two-dimensional dilaton theories. Dilaton theories are modifications of general relativity incorporating scalar fields called dilatons, which influence the strength of gravity. Physicists derive analytical expressions for the winding string solution, meticulously examining its geometric properties and establishing a clear connection to the near-horizon geometry of a Schwarzschild black hole in higher dimensions. The Schwarzschild black hole is a non-rotating, uncharged black hole described by a specific solution to Einstein’s field equations. This geometric correspondence suggests a deep relationship between these seemingly disparate objects, offering a potential pathway to understanding the ultimate fate of black holes and the preservation of information.

The investigation extends to obtaining an analytic solution for winding strings within the RST model, a specific framework within string theory known as the Ramond-Schild-Tucker model. This model provides a simplified setting for studying string dynamics. The analysis reveals the presence of background radiation analogous to the Hartle-Hawking vacuum surrounding a black hole. The Hartle-Hawking vacuum is a quantum state of spacetime, representing the lowest energy state in the presence of gravity. Importantly, the temperature of this radiation exhibits a consistency with that of the winding strings themselves, strengthening the connection between the string configuration and the black hole’s thermal properties and providing further evidence for the information preservation hypothesis.

The findings support the notion that black hole evaporation does not necessarily result in complete disappearance, but potentially culminates in a stable, string-like remnant. This offers a compelling alternative to the traditional view of black holes as cosmic dead ends. By providing an analytical description of self-gravitating strings and their associated radiation, this research offers a concrete model for the final stage of black hole evaporation.

Future research will focus on extending these results to higher dimensions and exploring the implications for the holographic principle—a conjecture suggesting that the description of a volume of space can be thought of as encoded on a lower-dimensional boundary—and the firewall paradox, which questions the validity of established principles of quantum mechanics near black hole horizons. Physicists plan to investigate the stability of these string remnants and their potential contribution to dark matter. They also aim to develop more realistic models of black hole evaporation that incorporate quantum gravity effects. This work represents a significant step forward in our understanding of black holes and the fundamental laws of physics.