The Ni’s Solution for Neutron Star and Outward Oriented Gravitational Attraction in Its Interior

In 2011, Jun Ni published the solution of the Tolman-Oppenheimer-Volkoff equations describing the structure of stable neutron stars, which implies that 1) there is no upper mass limit of these objects, 2) their outer physical surface is always situated above the corresponding event horizon, and 3) the object is a hollow sphere with the inner physical surface and cavity inside. In our paper, we propose to “purify” the general relativity, as the geometrical theory, from the concept of mass. If we get rid of the concept of mass and Newtonian-type potential, then we obtain such the behavior of gravity which results in the above mentioned stable Ni’s object. It is farther pointed out that the distribution of matter, which is observed as spherically symmetric by the observer in its center, is not longer observed as spherically symmetric by an observer aside the center in a curved spacetime of general relativity. This fact implies, in contrast to the Newtonian physics, the non-zero and outward oriented gravitational attraction of upper layers of star. Ni considered positive energy density and pressure. In addition, gravity had everywhere attractive character. No “exotic” assumption was made. Hence, there is no reason why his concept of hollow sphere should not be applicable to the models of real objects.

Center of Milky Way Galaxy

In 2013, World-Universe Model (WUM) made one of the most important predictions: “Macroobjects of the World have cores made up of the discussed DM (Dark Matter) particles. Other particles, including DM and baryonic matter, form shells surrounding the cores” [1]. Prof. R. Genzel and A. Ghez confirmed this prediction: “The Discovery of a Supermassive Compact Object at the Centre of Our Galaxy” (Nobel Prize in Physics 2020). On May 12, 2022, astronomers, using the Event Horizon Telescope, released the first image of the accretion disk around the Sagittarius A* (Sgr A*) produced using a worldwide network of radio observatories made in April 2017. These observations were obtained by a global array of millimeter wavelength telescopes and analyzed by an international research team that now numbers over 300 people, which claimed that Sgr A* is a Supermassive Black Hole (SBH). In the present paper, we analyze these results in frames of WUM. Based on the totality of all accumulated experimental results for the Center of the Milky Way Galaxy we conclude that Sgr A* is the DM Core of our Galaxy.

Relativistic compact stars with charged anisotropic matter

In this article, we perform a detailed theoretical analysis of new exact solutions with anisotropic fluid distribution of matter for compact objects subject to hydrostatic equilibrium. We present a family solution to the Einstein-Maxwell equations describing a spherically symmetric, static distribution of a fluid with pressure anisotropy.We implement an embedding class one condition to obtain a relation between the metric functions. We generalize the properties of a spherical star with hydrostatic equilibrium using the generalised Tolman-Oppenheimer-Volkoff(TOV)equation. We match the interior solution to an exterior Reissner-Nordstr?m one, and study the energy conditions,speed of sound, and mass-radius relation of the star. We also show that the obtained solutions are compatible with observational data for the compact object Her X-1. Regarding our results, the physical behaviour of the present model may serve for the modeling of ultra compact objects.

Durgapal IV model considering the minimal geometric deformation approach

The present article reports the study of local anisotropic effects on Durgapal's fourth model in the context of gravitational decoupling via the minimal geometric deformation approach.To achieve this,the most general equation of state relating the components of the−θsector is imposed to obtain the decoupler function f(r).In addition,certain properties of the obtained solution,such as the behavior of the salient material content threading the stellar interior;causality and energy conditions;hydrostatic balance through the modified Tolman−Oppenheimer−Volkoff conservation equation and stability mechanism against local anisotropies using the adiabatic index;sound velocity of the pressure waves;convection factor;and the Harrison−Zeldovich−Novikov procedure,are investigated to check whether the model is physically admissible or not.Regarding the stability analysis,it is found that the model presents unstable regions when the sound speed of the pressure waves and convection factor are used in distinction with the adiabatic index and Harrison−Zeldovich−Novikov case.To produce a more realistic picture,the numerical data for some known compact objects were determined and different values of the parameterαwere considered to compare with the GR case,i.e.,α=0.

Repeating fast radio bursts from collapses of the crust of a strange star

Strange stars(SSs)are compact objects made of deconfined quarks.It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS.Here we suggest that the intriguing repeating fast radio bursts(FRBs)are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion.The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario.Especially,the periodicity is attributed to the modulation of accretion rate through the disk instabilities.To account for a~16-day periodicity of the repeating FRB source of 180916.J0158+65,a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3×10^(16)gs^(-1) is invoked.Our scenario,if favored by future observations,will serve as indirect evidence for the strange quark matter hypothesis.

New self-consistent effective one-body theory for spinless binaries based on the post-Minkowskian approximation

The effective one-body theories, introduced by Buonanno and Damour, are novel approaches to constructing a gravitational waveform template. By taking a gauge in which ψ_(1)^(B) and ψ_(3)^(B) vanish, we find a decoupled equation with separable variables for ψ_(4)^(B) in the effective metric obtained in the post-Minkowskian approximation. Furthermore, we set up a new self-consistent effective one-body theory for spinless binaries, which can be applicable to any post-Minkowskian orders. This theory not only releases the assumption that v/c should be a small quantity but also resolves the contradiction that the Hamiltonian, radiation-reaction force, and waveform are constructed from different physical models in the effective one-body theory with the post-Newtonian approximation. Compared with our previous theory [Sci. China-Phys. Mech. Astron. 65, 260411(2022)], the computational effort for the radiation-reaction force and waveform in this new theory will be tremendously reduced.