Galactic Halo Region Research Articles

Gravitational lensing around dark matter in galactic halo region

The presence of dark matter in the galactic region has decisively confirmed by astronomical observations , however, the characteristics of dark matter yet to be recognized correctly. Utilizing the Einstein’s general theory of relativity and the observed rotational curve profile as input, we point out some features of galactic dark matter. Usually, dark matter is not directly visible but affects the lensing. In this paper, the deflection of a massive particle by galactic dark matter is studied using the Jacobi metric approach. We also provide a brief analysis of the image features of the deflection angle.

Generalized wormhole models within galactic halo region in torsion and matter coupling gravity formalism

In the current analysis, we investigate the possible existence of generalized Wormhole models within the galactic halo region by analyzing specific dark matter models. The observational data is checked in the framework of torsion within minimal matter coupling gravity. By using the variational approach modified versions of the field equations under the anisotropic source of matter are calculated. To discuss the specific necessary characteristics of the embedded wormhole geometry, we have analyzed the energy conditions under the effect of dark matter halos. We consider two embedded wormhole-specific shape functions in terms of the tortoise coordinate for the current study. Further, we compare different wormhole solutions for the different regional ranges depending on the involved parametric values. To check the effect of the dark matter halos, we use the observational data within the signature of the M87 galaxy and the Milky Way galaxy.

Dark matter supporting traversable wormholes in the Galactic halo

We study the Morris-Thorne traversable asymptotically flat and non-flat wormholes in the galactic halo of the Milky Way Galaxy(MWG) based on the Einasto dark matter(DM) density profile. Our reported shape function is positive and increasing in nature, moreover, satisfies all the essential wormhole representing conditions i.e. the reported shape function forms wormhole like structures in the galactic halo region of the MWG. Furthermore, the wormhole containing the DM candidate of the halo shelters wormholes by violating the null energy condition(NEC) with respect to three different redshift functions. The wormholes, namely, WH1 and WH2 corresponding to the first two choices of redshift functions are asymptotically flat while the WH3 corresponding to the third choice of redshift function is asymptotically non-flat. We, here, also analyze the ANEC violating matter content, embedding surface, and proper radial distance for our solutions.

Relativistic wormhole surrounded by dark matter halos in symmetric teleparallel gravity

AbstractIn this article we study the wormhole geometry in the galactic halo region under modified gravity, especially symmetric teleparallel gravity, where the nonmetricity scalar drives the gravitational interaction. The wormhole solutions for the assumed form have been presented, where α and β are the model parameters. The assumption of is based on the fact that its behavior should change with assumed parametric values of α as well as β within specific physical bounds. Two such models are presented based on the physically motivated shape function and energy conditions. We have elaborately shown, via mathematical calculations and graphical plots, the following features in our model: (i) energy conditions, especially NEC, which is very instructive in connection to energy violation in modified gravity theory, (ii) the wormhole solutions in the regime of Navarro‐Frenk‐White (NFW) density profiles for the galactic halo regions, (iii) treatment with particles moving in closed orbits around the wormholes which exhibit epicyclic frequencies, and (iv) the red‐blue shifts of the light coming from the wormhole throat in the vicinity of the dark matter halos. All the results and behaviors are satisfactory as well as interesting.

A galactic breeze origin for the Fermi bubbles emission

ABSTRACT The origin of the Fermi bubbles, which constitute two gamma-ray emitting lobes above and below the Galactic plane, remains unclear. The possibility that this Fermi bubbles gamma-ray emission originates from hadronic cosmic rays advected by a subsonic Galactic outflow, or breeze, is here explored. The simulation of a breeze solution and subsequent cosmic ray transport is carried out using the hydrodynamical code, PLUTO, in combination with a cosmic ray transport code. The Galactic outflow model obtained is found to be compatible with both inferences of the decelerating outflow velocity profile of the gas in the Fermi bubbles region, and evidence for the presence of a large amount of hot ionized gas out in the Galactic halo region. Although simple, this model is found to be able to reproduce the observed Fermi-LAT energy flux at high Galactic latitudes. Following these results a prediction concerning the gamma-ray emission for 1–3 TeV photons is made for future comparison with CTA/SWGO measurements.

Galactic Wormhole under Lovelock Gravity

We explore wormhole geometry in spiral galaxies under the third order Lovelock gravity. Using the cubic spline interpolation technique, we find the rotational velocity of test particles in the halo region of our spiral galaxy from observed values of radial distances and rotational velocities. Taking this value of the rotational velocity, we are able to show that it is possible to present a mathematical model regarding viable existence of wormholes in the galactic halo region of the Milky Way under the Lovelock gravity. A very important result that we obtain from the present investigation is that galactic wormhole in the halo region can exist with normal matter as well as exotic matter.

Charged perfect fluid dark matter model: Known mass density function approach

The concept of dark matter has been imported to explain the observed velocity profile of the spiral galaxies, the flat rotational velocity. Taking the flatness of rotation curves as an input and assuming that the galactic halo is filled with charged perfect fluid having known mass density function, we obtain a space time metric in the galactic halo region. The acquired solution indicates to a (nearly) flat universe, consistent with the present day cosmological observations. Various other aspects of the solution such as attractive gravity in the halo region, stability of the circular orbit, etc., are also analyzed.

Does dark matter admixed pulsar exist?

In this paper, we have considered a twofluid model assuming that the pulsars are made of ordinary matter admixed with dark matter.Contribution of dark matter comes from the fitting of the rotation curves of the SPARC sample of galaxies[95]. For this we have investigated the dark matter based on the Singular Isothermal Sphere (SIS) dark matter density profile in the galactic halo region. Considering this twofluid model, we have studied the physical features of the pulsars present in different galaxy in details. Here, we compute the probable radii, compactness (u) and surface red-shift (Zs) of the four pulsars namely : PSR J1748-2021B in NGC 6440B galaxy, PSR J1911-5958A in NGC 6752 galaxy, PSR B1802-07 in NGC 6539 galaxy and PSR J1750-37A in NGC 6441 galaxy.

Study of galactic halo F(T,TG) wormhole solutions

In this paper, we investigate static spherically symmetric wormhole solutions with galactic halo region in the background of [Formula: see text] gravity. Here, [Formula: see text] represents torsion scalar and [Formula: see text] is teleparallel equivalent Gauss–Bonnet term. For this purpose, we consider a diagonal tetrad and two specific [Formula: see text] models. We analyze the wormhole structure through shape function graphically for both models. We also investigate the behavior of null/weak energy conditions. Finally, we evaluate the equilibrium condition to check stability of the wormhole solutions. It is concluded that there exists physically viable wormhole solution only for the first model that turns out to be stable.

Wormhole solutions for f ( G ) $f(G)$ gravity in galactic halo region

In this paper, we study static spherically symmetric wormhole solutions in galactic halo region. Two observational results, Navarro–Frenk–White energy density profile in standard cosmological model and the observed flat rotational curves, are used to discuss traversable wormholes supported by galactic halo in modified Gauss–Bonnet gravity. We explore these solutions either by considering a viable $f(G)$ model to construct shape function or by specifying the shape function to deduce $f(G)$ model. We explore energy conditions and find physically acceptable wormhole solutions threaded by normal matter for all values of $r$ . Finally, we investigate stability of the resulting wormhole solutions.

Study of galactic rotation curves in wormhole spacetime

The spacetime of the galactic halo region is described by a wormhole like line element. We assume violation of Null Energy Condition (NEC) in the galactic halo. The Einstein Field equations are solved for two different conditions of pressure and density to obtain physical parameters like tangential velocity of test particles and parameters related to the wormhole geometry. The theoretical rotation curve of the test particles is plotted and compared the same with an observed rotation curve. We obtain a satisfactory fit between the observed curve and the curve obtained from the present theory for the radial distances in the range 9 Kpc to 100 Kpc.

Strong gravitational lensing in non-commutative wormholes

This paper is devoted to study gravitational lensing of static spherically symmetric non-commutative wormholes in galactic halo region. We formulate the field equations with anisotropic matter using particlelike source of gravitation in the form of Lorentzian distribution. We explore energy conditions and equilibrium condition of the wormhole model using generalized Tolman-Oppenheimmer-Volkov equation. To investigate position of wormhole, we evaluate angle of deflection in the strong field limit through numerical approach. It is found that the angle of deflection diverges for the photon radius.

Galactic Rotation Curves and Strange Quark Matter with Observational Constraints

We obtain the space time of the galactic core in the framework of general relativity by taking the flat rotational curve as input and considering the matter content in the galactic core region as strange quark matter. We also obtain the energy density, radial and tangential pressures of the core strange quark matter. Significantly we have shown that Bag Constant takes an important role to stabilize the circular orbit of the test particles. We also give a limit of the Bag constant for the existence of quark matter in the galactic halo region.

Possible features of galactic halo with electric field and observational constraints

Observed rotational curves of neutral hydrogen clouds strongly support the fact that galactic halo contains huge amount of nonluminous matter, the so called gravitational dark matter. The nature of dark matter is a point of debate among the researchers. Recent observations reported the presence of ions of O, S, C, Si etc. in the galactic halo and intergalactic medium. This supports the possibility of existence of electric field in the galactic halo region. We therefore propose a model of galactic halo considering this electric field arising due to charged particles as one of the inputs for the background spacetime metric. Considering dark matter as an anisotropic fluid we obtain the expressions for energy density and pressure of dark matter there and consequently the equation of state of dark matter. Various other aspects of the solutions are also analyzed along with a critical comparison with and constraints of different observational evidences.

Possible existence of wormholes in the galactic halo region

Two observational results, the density profile from simulations performed in the $\Lambda$CDM scenario and the observed flat galactic rotation curves, are taken as input with the aim of showing that the galactic halo possesses some of the characteristics needed to support traversable wormholes. This result should be sufficient to provide an incentive for scientists to seek observational evidence for wormholes in the galactic halo region.

Galactic Halo Wormhole Solutions inf(T)Gravity

The proposal of galactic halo region is based on the idea that dark halos contain some characteristics needed to support traversable wormhole solutions. We explore wormhole solutions in this region in the framework of generalized teleparallel gravity. We consider static spherically symmetric wormhole spacetime with flat galactic rotational curves and obtain expressions of matter components for nondiagonal tetrad. The effective energy-momentum tensor leads to the violation of energy conditions which may impose condition on the normal matter to satisfy these conditions. We take two well-knownf(T)models in exponential and logarithmic forms to discuss wormhole solutions as well as the equilibrium condition. It is concluded that wormhole solutions violating weak energy condition are obtained for both models with stable configuration.

Gamma ray and neutrino flux from the annihilation of neutralino dark matter at the Galactic halo region in the mAMSB model

We consider the lightest supersymmetric particle, the neutralino, in a minimal anomaly mediated supersymmetry breaking model to be a possible candidate for weakly interacting massive particles (WIMP) or cold dark matter, and we investigate its direct and indirect detections. The theoretically allowed supersymmetric parametric space for such a model, along with the recent bounds from the LHC, is constrained by the WMAP results for relic densities. The spin-independent and spin-dependent scattering cross sections for dark matter off nucleons are thus constrained from the WMAP results. They are found to be within the allowed regions of different ongoing direct detection experiments. The annihilation of such dark-matter candidates at the Galactic centre produces different standard model particles such as γ-rays and neutrinos. In this work, we calculate the possible fluxes of these γ-rays and neutrinos coming from the direction of the Galactic centre (and its neighbourhood) at terrestrial or satellite-borne detectors. The calculated γ-ray flux is compared with the observational results of the HESS experiment. The neutrino fluxes of different flavours from the Galactic centre and at different locations away from the Galactic centre produced by WIMP annihilation in this model are also obtained for four types of Galactic dark-matter halo profiles. The detection prospects of such νμ coming from the direction of the Galactic centre at the ANTARES under-sea detector are discussed in terms of the muon signal yield from these muon neutrinos. Both the γ-ray and neutrino signals are estimated for four different dark-matter halo profiles.

Quark matter as dark matter in modeling galactic halo

Considering the flat rotation curves as input and treating the matter content in the galactic halo region as quark matter, we have found out a background spacetime metric for the region of the galactic halo. We obtain fairly general conditions that ensure that gravity in the halo region is attractive. We also investigate the stability of circular orbits, along with a different role for quark matter. Bag-model quark matter meeting these conditions therefore provides a suitable model for dark matter.

Perfect fluid dark matter

Taking the flat rotation curve as input and treating the matter content in the galactic halo region as perfect fluid we obtain a space–time metric at the galactic halo region in the framework of general relativity. We find that the resultant space–time metric is a non-relativistic dark matter induced space–time embedded in a static Friedmann–Lemaître–Robertson–Walker universe i.e. the flat rotation curve not only leads to the existence of dark matter but also suggests about the background geometry of the universe. Within its range of validity the flat rotation curve and the demand that the dark matter to be non-exotic together indicate for a (nearly) flat universe as favored by the modern cosmological observations. We obtain the expressions for energy density and pressure of dark matter there and consequently the equation of state of dark matter. Various other aspects of the solutions are also analyzed.