Shadows and precession of orbits in rotating Janis–Newman–Winicour spacetime

Abstract

In this paper, we construct the rotating Janis–Newman–Winicour (JNW) naked singularity spacetime using Newman–Janis Algorithm (NJA). We analyse NJA with and without complexification methods and find that the energy conditions do satisfied when we skip the complexification step. We study the shadows cast by rotating JNW naked singularity and compare them with the shadows cast by the Kerr black hole. We find that the shadow of the rotating naked singularity can be distinguished from the shadow of the Kerr black hole. While we analyse the precession of timelike bound orbits in rotating JNW spacetime, we find that it can have a negative (or opposite) precession, which is not present in the Kerr black hole case. These novel signatures of the shadow and orbital precession in rotating JNW naked singularity spacetime could be important in the context of the recent observation of the shadow of the M87 galactic center and the stellar dynamics of ‘S-stars’ around Milkyway galactic center.

Toward General Relativistic Magnetohydrodynamics Simulations in Stationary Nonvacuum Spacetimes

“…This form of the metric can be used as an input when performing general relativistic (GR), as well as non-GR, magnetohydrodynamics simulations of accretion flows onto compact objects in arbitrary metric theories of gravity. The AA metric can be used to generate a number of popular metrics that describe the stationary spacetimes in GR corresponding to electrovacuum black holes (BHs; Kerr 1963;, regular BHs such as the Kerr-Hayward models (Hayward 2006;Bambi & Modesto 2013;Zhou & Modesto 2023a, 2023b, naked singularities such as the spinning Janis-Newman-Winicour spacetime (Solanki et al 2022), etc. It can also be used to describe BH solutions arising in alternative theories of gravity (e.g., Sen 1992).…”

“…This metric, therefore, presents an excellent starting point for a broad forward-modeling study of the effect of the spacetime metric on various observables of interest. The Liouville separability of the null geodesic equations makes computing various characteristic features of the spacetime, such as the location of the photon shell or the shape of the shadow boundary (see, e.g., Shaikh 2019;Kocherlakota et al 2021;Solanki et al 2022), analytically tractable. Similarly, the separability of the time-like orbits facilitates a study of, e.g., equatorial Keplerian orbits and allows us to go one step further with semianalytic techniques.…”

Energy extraction from Janis-Newman-Winicour naked singularity

“…The extended geometry of Schwarzschild spacetime with a massless scalar field is known as Janis-Newman-Winicour spacetime. The rotating version of the JNW metric is derived in [92], using Newman-Janis Algorithm (NJA) without complexification. The rotating JNW naked singularity spacetime can be written as,…”

Precessing and periodic orbits around hairy black holes in Horndeski’s Theory

“…: V,-vol whirl structure for the periodic motions has not been apparently observed, the periodic motions might offer computational advantages for adiabatic extreme mass-ratio inspirals [109] and the unique information about some properties of the spacetime in the strong gravitational field that is unavailable from the precessing motions. The periodic motions have widely been investigated in Kerr [108], Reissner-Nordström [110] and others black holes [111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128]. Particularly, the discovery of some stars around Sgr A* in the present and the near future has made it possible to use their precessing and periodic motions for probing the curved spacetime of one black hole [103,[129][130][131][132][133][134].…”