In this work, we obtain the shadow images of spherically symmetric scalar boson and Proca stars using analytical fittings numerical solutions, when illuminated by a geometrically thin accretion disk. We chose sample four with radii ranging from more compact configurations $R\ensuremath{\sim}9M$ to dilute $R\ensuremath{\sim}20M$, where $M$ is total mass bosonic star. these configurations, absence light sphere (the locus unstable bound geodesics) makes optical appearance be dominated single...

In this work we consider the observational properties of compact boson stars with self-interactions orbited by isotropically emitting (hot-spot) sources and optically thin accretion disks. We two families supported quartic sixth-order self-interaction potentials, choose three samples each them in growing compactness; only those large enough compactness are capable to hold light rings, namely, null bound orbits. For hot spots, using inclination angles...

Abstract The optical appearance of a body compact enough to feature an unstable bound orbit, when surrounded by accretion disk, is expected be dominated luminous ring radiation enclosing central brightness depression typically known as the shadow. Despite observational limitations, rough details this picture have been now confirmed results Event Horizon Telescope (EHT) Collaboration on imaging M87 and Milky Way supermassive objects. However, precise characterization both features—ring...

In this work we analyze the observational properties of incompressible relativistic fluid spheres with and without thin-shells when surrounded by thin accretion disks. We consider a set six configurations different combinations star radius $R$ thin-shell ${r}_{\mathrm{\ensuremath{\Sigma}}}$ to produce solutions neither nor light-rings, either those features, both. Furthermore, three models for intensity profile disk, based on Gralla-Lupsasca-Marrone (GLM) disk model, which peaks occur at...

Wormhole solutions in a generalized hybrid metric-Palatini matter theory, given by gravitational Lagrangian $f\left(R,\cal{R}\right)$, where $R$ is the metric Ricci scalar, and $\mathcal{R}$ Palatini scalar curvature defined terms of an independent connection, Lagrangian, are found. The worked scalar-tensor representation field traded for two scalars, $\varphi$ $\psi$, term maintained. main interest found that obeys null energy condition (NEC) everywhere, including throat up to infinity, so...

Ultralight scalars can extract rotational energy from astrophysical black holes through superradiant instabilities, forming macroscopic boson clouds. This process is most efficient when the Compton wavelength of comparable to size hole horizon, i.e., ``gravitational fine structure constant'' $\ensuremath{\alpha}\ensuremath{\equiv}G\ensuremath{\mu}M/\ensuremath{\hbar}c\ensuremath{\sim}1$. If hole/cloud system in a binary, tidal perturbations companion produce resonant transitions between...

In this work we derive the junction conditions for matching between two spacetimes at a separation hypersurface in perfect-fluid version of $f\left(R,T\right)$ gravity, not only usual geometrical representation but also dynamically equivalent scalar-tensor representation. We start with general case which thin-shell separates hypersurface, are deduced, and particular smooth is considered when stress-energy tensor vanishes. The set similar to one previously obtained $f\left(R\right)$ gravity...

In this work we analyze traversable wormhole solutions in the linear form of $f\left(R,T\right)=R+\lambda T$ gravity satisfying Null, Weak, Strong, and Dominant Energy Conditions (NEC, WEC, SEC, DEC respectively) for entire spacetime. These are obtained via a fully analytical parameter space analysis free parameters model, namely exponents controlling degree redshift shape functions, radius throat $r_0$, value function at $\zeta_0$, coupling $\lambda$. Bounds on these which energy conditions...

Pushed by a number of advances, electromagnetic observatories have now reached the horizon scale supermassive black holes. The existence and properties horizons in our universe is one outstanding fundamental issues that can be addressed. Here we investigate ability to discriminate between holes compact, horizonless objects, focusing on lensing hot spots around compact objects. We work particular with boson Proca stars as central show absence gives rise characteristic feature---photons plow...

In this work, we analyze the observational properties of thin-shell gravastars under two astrophysical frameworks, namely surrounded by optically thin accretion disks and orbited hot spots. We consider gravastar model with free parameters, radius ratio mass allocated at thin-shell, produce corresponding observables via use numerical backwards ray-tracing codes. Regarding observations disks, our results indicate that, due to absence a strong gravitational redshift effect, smooth...

In this work, we study spherically symmetric vacuum solutions in one-parameter new general relativity (NGR), a specific theory teleparallel gravity which is constructed from the three possible quadratic scalars obtained torsion with arbitrary coefficients satisfying requirements for absence of ghosts. class modified theories gravity, observable effects result rather than curvature spacetime. Unlike GR, where fundamental quantity metric Levi-Civita connection derived, variable tetrad, one...

The Aether scalar tensor (AeST) theory is an extension of general relativity, proposed for addressing galactic and cosmological observations without dark matter. action the includes a function that can currently only be constrained by phenomenological considerations. In antecedent work, forms this were considered led to effective fluid contribution evolution equations approximated dust more closely at late cosmic times. work we consider alternative set functions most approximate earliest...

Black holes in General Relativity are described by space-time metrics that simpler comparison to non-vacuum compact objects. However, given the universality of gravitational pull, it is expected dark matter accumulates around astrophysical black holes, which can have an impact overall field, especially at galactic centers, and induce non-negligible effects their observational imprints. In this work we study optical appearance a spherically symmetric hole both when orbited isotropically...

In this work, we use the dynamical system approach to explore cosmological background evolution of scalar-tensor representation f (R, T ) gravity, where R is Ricci scalar and trace stress-energy tensor.The motivation for work resides in finding behaviors comparable with ΛCDM model without necessity recurring a dark energy component.We introduce set variables that allow direct comparison standard current experimental measurements, develop framework analyze Friedmann-Lemaître-Robertson-Walker...

In this work we analyze the observational properties of relativistic fluid spheres when orbited by isotropically emitting sources, known as hot spots. We consider star configurations in four different regimes compacticity, from Buchdahl limit to nonultracompact solutions, thus obtaining stars with qualitatively geodesic structures and properties. show that for at are similar ones Schwarzschild black hole, whereas more dilute one can find other fundamentally models, e.g., bosonic without self...

We construct exact solutions representing a Friedmann-Lema\^itre-Robsertson-Walker (FLRW) universe in generalized hybrid metric-Palatini theory. By writing the gravitational action scalar-tensor representation, new are obtained by either making an ansatz on scale factor or effective potential. Among other relevant results, we show that it is possible to obtain exponentially expanding for flat universes even when cosmology not purely vacuum. then derive classes of actions original theory...

In this work, we use reconstruction methods to obtain cosmological solutions in the recently developed scalar-tensor representation of $f(R,T)$ gravity. Assuming that matter is described by an isotropic perfect fluid and spacetime homogeneous isotropic, i.e., Friedmann-Lema\^itre-Robsertson-Walker (FLRW) universe, energy density, pressure, scalar field associated with arbitrary dependency action $T$ can be written generally as functions scale factor. We then select three particular forms...

In this work, we study the possibility of finite-time future cosmological singularities appearing in $f(R,T)$ gravity, where $R$ is Ricci scalar and $T$ trace stress-energy tensor. We present theory both geometrical dynamically equivalent scalar-tensor representation obtain respective equations motion. a background Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) universe with an arbitrary curvature for generic $C^\infty$ function $f(R,T)$, prove that conservation tensor prevents appearance...

Abstract In this work we analyze traversable wormhole spacetimes in the framework of a covariant generalization Einstein’s General Relativity known as energy–momentum squared gravity, or $$f\left( R,{\mathcal {T}}\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>f</mml:mi> <mml:mfenced> <mml:mi>R</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> </mml:mfenced> </mml:mrow> </mml:math> where R is Ricci scalar, $${\mathcal {T}}=T_{ab}T^{ab}$$...

In this work we present a general method to obtain the junction conditions of modified theories gravity whose action can be written in form $f({X}_{1},\dots{},{X}_{n})$, where ${X}_{1}$ ${X}_{n}$ are any combination scalar dependencies, e.g., Ricci $R$, trace stress-energy tensor $T$, Gauss-Bonnet invariant $\mathcal{G}$, among others. We discriminate into three subgroups: immediate conditions, arising from imposition regularity relevant quantities distribution formalism; differential terms...

In this work, we explore the existence of traversable wormhole solutions supported by double gravitational layer thin shells and satisfying null energy condition (NEC) throughout whole spacetime, in a quadratic-linear form generalized hybrid metric-Palatini gravity. We start showing that for particular action, junction conditions on continuity Ricci scalar $R$ Palatini $\mathcal{R}$ theory can be discarded without appearance undefined distribution terms field equations. As consequence, shell...

It has long been known that dissipation is a crucial ingredient in the superradiant amplification of wave packets off rotating objects. We show that, once appropriate mechanisms are included, stars also prone to superradiance and instabilities. In particular, ultralight dark matter with small interaction cross section star material or self-annihilation can trigger instability. On time scales, instability strips most its angular momentum. Whether not new stationary configurations surrounded...

It is shown that the Kerr solution exists in generalized hybrid metric-Palatini gravity theory and for certain choices of function $f(R,\mathcal{R})$ characterizes theory, can be stable against perturbations on scalar degree freedom theory. We start by verifying which are most general conditions allow relativistic to also a this perform perturbation trace metric tensor, turn imposes both Ricci Palatini curvatures. To first order perturbation, equations motion, namely field equation relates...

Braneworld scenarios consider our observable universe as a brane embedded in five-dimensional bulk. In this work, we thick braneworld systems the recently proposed dynamically equivalent scalar-tensor representation of $f(R,T)$ gravity, where $R$ is Ricci scalar and $T$ trace stress-energy tensor. general $f\left(R,T\right)$ case two different models: model without matter fields geometry supported solely by gravitational fields, second described field with potential. The particular cases for...