High-Energy Extractions from Horizonless Compact Objects

TL;DR

The paper surveys energy-extraction mechanisms in horizonless compact objects, emphasizing how Penrose-type processes, magnetic extensions, BZ/MHD jets, and collisional effects operate without an event horizon. It highlights naked singularities, especially rotating JNW spacetimes, as laboratories where magnetic coupling and negative-energy orbits can yield higher efficiencies or unbounded energies via the super-Penrose process. A key message is that horizonless geometries fundamentally alter energy-release dynamics, offering potential explanations for extreme high-energy phenomena and making distinctive observational predictions. The work underscores the role of horizonless engines as natural laboratories for strong-field gravity and as alternative drivers of high-energy astrophysical emission in the era of multi-messenger astronomy.

Abstract

High-energy astrophysical sources such as active galactic nuclei, quasars, X-ray binaries, and gamma-ray bursts are powered by mechanisms that convert gravitational or rotational energy into radiation, jets, and relativistic outflows. Understanding the physics of these processes remains a major challenge. Black holes have traditionally served as the central engines behind such phenomena, with well established energy extraction mechanisms including the Penrose process, the Blandford-Znajek process, and the Banados-Silk-West mechanism. However, studies in general relativity indicate that, under certain conditions, gravitational collapse may lead to the formation of naked singularities or other horizonless compact objects, which could in principle allow more efficient energy extraction than classical black holes. This brief review summarizes recent progress on energy extraction mechanisms in naked singularity spacetimes. We examine the roles of rotation, electromagnetic fields, and particle interactions in shaping extraction efficiency and dynamics. Particular attention is given to negative energy orbits and ergoregion physics, which enable Penrose type and magnetic Penrose mechanisms without an event horizon. We also discuss collisional Penrose processes and particle acceleration near the singularity, emphasizing their potential astrophysical implications. By comparing extraction efficiencies and physical conditions in black holes and naked singularities, we highlight how the absence of a horizon fundamentally alters the dynamics of energy release. These results suggest that naked singularities may serve as natural laboratories for strong field gravity and as alternative engines for high-energy astrophysical phenomena in the era of multi-messenger observations.