Dark Matter Medium Research Articles

Shadow and deflection angle of asymptotic, magnetically-charged, non-singular black hole

In this paper, we investigate a solution for an asymptotic, magnetically-charged, non-singular (AMCNS) black hole. By utilizing the Gauss–Bonnet theorems, we aim to unravel the intricate astrophysics associated with this unique black hole. The study explored various aspects including the black hole’s gravitational field, intrinsic properties, light bending, the shadow and greybody bounding of the black hole. Through rigorous calculations and simulations, we derive the weak deflection angle of the optical metric of AMCNS black hole. Additionally, we investigate the impact of the dark matter medium on the deflection angle, examined the distinctive features of the black hole’s shadow, and bound its greybody factors. Our findings not only deepen our understanding of gravitational lensing but also pave the way for future improvements in black hole theories by minimizing restrictive assumptions and incorporating a more realistic representation of these cosmic phenomena.

Weak deflection angle of black-bounce traversable wormholes usingGauss–Bonnet theorem in the dark matter medium

In this paper, we first use the optical metrics of black-bounce traversable wormholes to calculate the Gaussiancurvature. Then we use the Gauss–Bonnet theorem to obtain the weak deflection angle of light from the black-bouncetraversable wormholes. We investigate the effect of dark matter medium on weak deflection angle using the Gauss–Bonnet theorem. We show how weak deflection angle of wormhole is affected by the bounce parametera. Using theGauss–Bonnet theorem for calculating weak deflection angle shows us that light bending can be thought as a global andtopological effect.

Testing self-interacting dark matter with galaxy warps

Self-interacting dark matter (SIDM) is an able alternative to collisionless dark matter. If dark matter does have self-interactions, we would expect this to cause a separation between the collisionless stars and the dark matter halo of a galaxy as it falls through a dark matter medium. For stars arranged in a disk, this would generate a U-shaped warp. The magnitude of this warping depends on the SIDM cross section, type of self-interaction, relative velocity of galaxy and background, halo structure, and density of the dark matter medium. In this paper, we set constraints on long-range (light mediator) dark matter self-interaction by means of this signal. We begin by measuring U-shaped warps in $3,213$ edge-on disk galaxies within the Sloan Digital Sky Survey. We then forward-model the expected warp from SIDM on a galaxy-by-galaxy basis by combining models of halo structure, density and velocity field reconstructions, and models for the dark matter interactions. We find no evidence for a contribution to the warps from SIDM. Our constraints are highly dependent on the uncertain velocities of our galaxies: for a normalized Rutherford-like cross section we find $\tilde{\sigma}/m_{\rm{DM}} \lesssim 3\times 10^{-13}~\rm{cm}^2/\rm{g}$ at fixed velocity $v = 300~\rm{km/s}$ -- a bound that scales roughly linearly with increasing $v$. In the appendix we translate these bounds into limits on the momentum transfer cross section, finding $\sigma_T(300~\rm{km/s})/m_{\rm{DM}} \lesssim 0.1~\rm{cm}^2/\rm{g}$. [abridged]

Deflection Angle of Photons through Dark Matter by Black Holes and Wormholes Using Gauss–Bonnet Theorem

In this research, we used the Gibbons–Werner method (Gauss–Bonnet theorem) on the optical geometry of a black hole and wormhole, extending the calculation of weak gravitational lensing within the Maxwell’s fish eye-like profile and dark-matter medium. The angle is seen as a partially topological effect, and the Gibbons–Werner method can be used on any asymptotically flat Riemannian optical geometry of compact objects in a dark-matter medium.

Phenomenology of dark matter via a bimetric extension of general relativity

We propose a relativistic model of dark matter reproducing at once the concordance cosmological model $\mathrm{\ensuremath{\Lambda}}$-cold-dark-matter ($\mathrm{\ensuremath{\Lambda}}\text{\ensuremath{-}}\mathrm{CDM}$) at cosmological scales and the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. To achieve this we postulate a nonstandard form of dark matter, consisting of two different species of particles coupled to gravity via a bimetric extension of general relativity and linked together through an internal vector field (a ``graviphoton'') generated by the mass of these particles. We prove that this dark matter behaves like ordinary cold dark matter at the level of first-order cosmological perturbation, while a pure cosmological constant plays the role of dark energy. The MOND equation emerges in the nonrelativistic limit through a mechanism of gravitational polarization of the dark matter medium in the gravitational field of ordinary matter. Finally we show that the model is viable in the Solar System as it predicts the same parametrized post-Newtonian parameters as general relativity.

Very old isolated compact objects as dark matter probes

Very old isolated neutron stars and white dwarfs have been suggested to be probes of dark matter. To play such a role, two requests should be fulfilled, i.e., the annihilation luminosity of the captured dark matter particles is above the thermal emission of the cooling compact objects (request-I) and also dominate over the energy output due to the accretion of normal matter onto the compact objects (request-II). Request-I calls for very dense dark matter medium and the critical density sensitively depends on the residual surface temperature of the very old compact objects. The accretion of interstellar/intracluster medium onto the compact objects is governed by the physical properties of the medium and by the magnetization and rotation of the stars and may outshine the signal of dark matter annihilation. Only in a few specific scenarios both requests are satisfied and the compact objects are dark matter burners. The observational challenges are discussed and a possible way to identify the dark matter burners is outlined.

Dark matter structures and emission of very long gravitational waves

Formation of large structure in the Universe as a result of gravitational instability in cold dark matter is investigated in a simple analytical model. Collapse of the rotating spheroid is approximated by a system of ordinary differential equations describing its dynamics. The gravitational potential is approximated by the one of the uniform Maclaurin spheroid. Development of gravitational instability and collapse in tlie dark matter medium do not lead to any shock formation or radiation, but is characterized by non-colliskmal relaxation, which is accompanied by the mass and angular momentum losses. Phenomenological account of these processes is done in this model. Formation of the equilibrium configuration dynamics of collapse is investigated. A very long gravitational wave emission during the collapse is estimated, and their possible connection with the observed gravitational lenses is discussed.

A simplified model of the formation of structures in dark matter and a background of very long gravitational waves

Collapse of the rotating spheroid is approximated by a system of ordinary differential equations describing its dynamics. The gravitational potential is approximated by the one of the iniform Maclaurin spheroid. Developement of gravitational instability and collapse in the dark matter medium do not lead to any shock formation or radiation, but is characterized by non-collisional relaxation, which is accompanied by the mass and angular momentum losses. Phenomenological account of these processes is done in this model. Formation of the equilibrium configuration dynamics of collapse is investigated for several parameters, characterizing the configuration. A very long gravitational wave emission during the collapse is estimated, and their possible connection with the observed gravitational lenses is discussed.