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The present study investigates the negative energy orbits and energy extraction efficiency using the magnetic Penrose process in various regular black hole geometries surrounded by electromagnetic fields. Utilizing numerical simulations, we analyze the efficiency of this process in Kerr and Simpson-Visser geometries, focusing on extremal black holes. Interestingly, our study demonstrates that the energy extraction efficiency remains indistinguishable between Kerr and Simpson-Visser geometries, regardless of the regularization parameter ($l$); this trend is consistent with previous studies of the Penrose process and superradiance. Additionally, we present results for the rotating Hayward black hole, showing that efficiency is influenced by spin and deviation parameters ($g$), as well as the induced magnetic field and charge of the compact object. Notably, we observe that energy extraction efficiency is highest in the rotating Hayward black hole compared to Kerr and Simpson-Visser geometries, particularly in scenarios where the magnetic field and charge are minimal. Our study highlights the significant role of spin, charge and magnetic field characteristics in maximizing energy extraction efficiency, particularly in the rotating Hayward black hole context., Comment: 12 pages, 5 figures and 2 tables (comments are welcome!)

The source of Ultra-High Energy Cosmic Rays (UHECRs) remains one of the greatest mysteries in astrophysics. Their possible source can be the galactic nuclei, where the ultra-high gravity region plays a crucial role. Cosmic rays are extremely energetic particles that travel through space with energies exceeding $10^{20}eV$, but their origin is still a mystery despite years of studies and observations. In view of this, in this work, we studied the Joshi-Malafarina-Narayan (JMN-1) naked singularity as a natural particle accelerator. We derived the necessary expressions to find center of mass energy when two particles collide. We have obtained results showing that center of mass energy of the two particles will reach to Planck energy scale. This will form a microscopic black hole which will decay in Hawking radiation, having energy on the order of $10^{26} eV$ from the ultra-high gravity region of Sgr A*. These outgoing highly energetic particles from the naked singularity could be the possible sources of UHECRs., Comment: Calculation errors

In general, energy extraction methods such as the Penrose process and the magnetic Penrose process are thought to be reliant on the existence of an ergoregion. Inside an ergoregion, there are negative energy states that allow a particle to extract energy and escape to an observer at infinity. In this paper, we considered the electromagnetic field in the rotating Janis-Newman-Winicour (JNW) spacetime. This concept is feasible because an accretion disc forms an electromagnetic field around compact objects. After that, we briefly examine negative energy orbits and their significance in energy extraction. The ergoregion is absent in a rotating JNW geometry, but we show that the effective ergoregion is there. The change in a negative energy orbit concerning the magnetic field (B), spin parameter (a), and electric charge (Q) is analyzed. We find that the total energy extraction efficiency within this process can be around $60\%$ for the rotating JNW naked singularity., Comment: 11 pages, 18 figures

In this paper, we investigate the light trajectories and shadow properties in the rotating version of null naked singularity (NNS) spacetime which is derived using the Newman- Janis algorithm without complexification method. We discuss some of the geometrical properties and causal structure of Rotating Naked Singularity (RNS) spacetime. The gravitational lensing in a rotating naked singularity is analyzed, and the results are compared to those of a Kerr black hole. In the case of a Kerr black hole, the photon sphere exists for both prograde and retrograde photon orbits, whereas for RNS, the photon sphere exists only for retrograde photon orbits. As a result, the naked singularity projects an arc-shaped shadow that differs from the contour-shaped shadow cast by a Kerr black hole., Comment: 12 pages, 4 figures

In this paper, the Penrose process is being used to extract rotational energy from regular black holes. Initially, we consider the rotating Simpson-Visser regular spacetime which describes the class of geometries of the Kerr black hole's mimickers. The Penrose process is then studied through conformally transformed rotating singular and regular black hole solutions. These both Simpson-Visser and conformally transformed geometries depend on mass, spin, and an additional regularisation parameter $l$. In both cases, we investigate how the spin and regularisation parameter $l$ affects the configuration of an ergoregion and event horizons. Surprisingly, we find that the energy extraction efficiency from the event horizon surface is not dependent on the regularisation parameter $l$ in the Simpson-Visser regular spacetimes and hence it does not vary from the Kerr black hole case. While, in the conformally transformed singular and regular black holes, we obtain the efficiency rate of extracted energies are extremely high compared to the Kerr black hole scenario. This distinct signature of the conformally transformed singular and regular black holes would be useful to distinguish them from the Kerr black hole in observation., Comment: 16 pages, 23 figures