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Circular orbit specific angular momentum lK+ given by equation (17) for various boson stars (upper row, bottom left panel), together with the same quantity for the Kerr metric with a/M = 0.9 (bottom right panel). Boson star angular momenta are plotted for r > rICO while the Kerr angular momentum is plotted for all radii above the horizon.
Source publication
Accretion disks play an important role in the evolution of their relativistic
inner compact objects. The emergence of a new generation of interferometers
will allow to resolve these accretion disks and provide more information about
the properties of the central gravitating object. Due to this instrumental leap
forward it is crucial to investigate...
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Citations
... One way to detect them would be by indirect observation of the accretion disks that could form around them, in case that one could distinguish these accretion disks from those that would form around other objects like black holes. In that regard, they may possess bound circular orbits which also extend into the inner regions with high density of the scalar field distribution in contrast to black holes [37]. Additionally, the formation of a shadow in the strict sense would be prevented since they are horizonless, but nevertheless (in the presence of accretion disks) a central dark region will be observed similar to that of black holes, which corresponds to the lensed image of an accretion disk's inner edge [38][39][40][41]. ...
Boson stars are considered as promising candidates for black hole mimickers. Similar to other compact objects they can form accretion disks around them. The properties of these disks could possibly distinguish them from other compact objects like black holes in future observations. Retrograde thick disks around boson stars and the influence of strong magnetic fields on them were already studied and it was shown that they can harbor very distinct features compared to black hole disks. However, the case of prograde thick disks is mostly unexplored, since they may appear much more similar to black hole disks. In this work we will investigate similarities and differences regarding prograde thick disks around non-selfinteracting rotating boson stars and rotating black holes. We assume thereby a polytropic equation of state and a constant specific angular momentum distribution of the disks. We classify the various conceivable boson star and black hole solutions by a dimensionless spin parameter a and compare their corresponding disk solutions. The influence of toroidal magnetic fields on the disks is analyzed by selected disk properties, as the rest-mass density distribution and the Bernoulli parameter. Disk solutions are characterized by their degree of magnetization represented by the magnetization parameter $$\beta _{mc}$$ β mc . We found that strong magnetic fields can strengthen the differences of disk solutions or oppositely even lead to a correlation in disk properties, depending on the spin parameter of the boson star and black hole solutions. We identify the vertical thickness of the boson star disks as the main differentiating factor, since for most solutions the vertical density distribution is far more outreaching for boson star disks compared to black hole disks.
... Some BS configurations also feature photon spheres around them, which is otherwise seen as a characteristic feature of black hole spacetimes [157]. According to a number of simulations [17,156,158], they would however show distinguishable torus accretion dynamics compared to black holes. Since BS do not have an event horizon, matter could accumulate in the centre of boson stars, leaving clear imprints of radiating matter inside the BS [159,160,161], for example in form of thermal or X-ray radiation [162]. ...
It is believed that dark matter (DM) could accumulate inside neutron stars and significantly change their masses, radii and tidal properties. We study what effect bosonic dark matter, modelled as a massive and self-interacting scalar or vector field, has on neutron stars. We derive equations to compute the tidal deformability of the full Einstein-Hilbert-Klein-Gordon system self-consistently, and probe the influence of the scalar field mass and self-interaction strength on the total mass and tidal properties of the combined system, called fermion boson stars (FBS). We are the first to combine Proca stars with neutron stars to mixed systems of fermions and a vector field in Einstein-Proca theory, which we name fermion Proca stars (FPS). We construct equilibrium solutions of FPS, compute their masses, radii and analyse them regarding their stability and higher modes. We find that FPS tend to be more massive and geometrically larger than FBS for equal boson masses and self-interaction strengths. Both FBS and FPS admit DM core and DM cloud solutions and we find that they can produce degenerate results. Core solutions compactify the neutron star component and lower their tidal deformability, cloud solutions have the inverse effect. Electromagnetic observations of certain cloud-like configurations would appear to violate the Buchdahl limit. The self-interaction strength is found to significantly affect both mass and tidal deformability. We discuss observational constraints and the connection to anomalous detections. We also show how models with an effective equation of state compare to the self-consistent solution of FBS and find the self-interaction strength where both solutions converge sufficiently.
... If indeed a boson star collapses to a BH, then one could hope to observe the QNM of the massive scalar field, as described in Hod (2011). Differences between accretion structures surrounding boson stars and black holes are analyzed in Meliani et al. (2015), showing that the accretion tori around boson stars have different characteristics than in the vicinity of a black hole. Similar differences have been reported regarding tidal disruption clouds orbiting either a spherically symmetric compact boson star or a Schwarzschild black hole (Teodoro et al. 2021). ...
The idea of stable, localized bundles of energy has strong appeal as a model for particles. In the 1950s, John Wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called geons, but none were found. Instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name boson stars. Since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single Killing vector. We discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts.
... For instance, the properties -either equilibrium or dynamical -of geometrically thick tori have been explored in Schwarzschild-de-Sitter spacetimes (Rezzolla et al. 2003b;Stuchlik et al. 2009), in (Newman-Unti-Tamburino) NUT spacetimes (Jefremov & Perlick 2016), in spherically symmetric spacetimes in ( )-gravity (Cruz-Osorio et al. 2021), around Kerr black holes with a scalar hair (Gimeno-Soler et al. 2019;Gimeno-Soler et al. 2021;Teodoro et al. 2021b), or more recently in the so-calledmetric (Faraji & Trova 2021;Memmen & Perlick 2021) 1 . Finally, equilibrium tori also have been investigated around ultra-compact objects different from black holes, such as boson stars (Meliani et al. 2015;Olivares et al. 2020;Teodoro et al. 2021a), or naked singularities in Kerr-de Sitter spacetimes Stuchlík et al. (2015). ...
Non-selfgravitating equilibrium tori orbiting around black holes have a long history and have been employed in numerous simulations of accretion flows onto black holes and other compact objects. We have revisited the problem of constructing such equilibria starting from spherically symmetric black-hole spacetimes expressed in terms of a fully generic and rapidly converging parameterisation: the RZ metric. Within this framework, we have extended the definitions of all of the quantities characterising these equilibria, starting from the concept of the von Zeipel cylinders and up to the possible ranges of the specific angular momenta that are employed to construct families of tori. Within the allowed space of parameters we have then encountered both standard ``single-torus'' solutions, but also non-standard ``double-tori'' solutions. While the properties of the first ones in terms of the presence of a single cusp, of a local pressure maximum and of a varying outer radius, are very similar to those encountered in general relativity, the properties of double-tori solutions are far richer and naturally allow for configurations having the same constant specific angular momentum and hence are potentially easier to produce in nature. The existence of these objects is at present very hypothetical, but these equilibrium tori were to be observed, they would provide very valuable information on the properties of the spacetime and on its deviation from general relativity.
... They produce a strong gravitational field and negligible electromagnetic emission, in this way they are mimicking the properties of black holes. Various boson star configurations have been constructed [31][32][33][34][35][36][37][38][39][40], and their properties were investigated such as stability [41][42][43], geodesic motion [44][45][46][47][48][49] and tidal effects in the motion of gas clouds around them [50,51]. Since they are horizonless compact objects, which are not characterized by a solid boundary but rather by a decaying profile of the scalar field density towards infinity, the particles and light propagation in their vicinity is specific leading to phenomenological signatures. ...
... Since they are horizonless compact objects, which are not characterized by a solid boundary but rather by a decaying profile of the scalar field density towards infinity, the particles and light propagation in their vicinity is specific leading to phenomenological signatures. For example, boson stars may possess only bound circular orbits which extend into the inner regions with high density of the scalar field distribution [47]. In addition, photon rings may be absent which prevents the formation of a shadow in the strict sense. ...
... The perfect fluid equilibrium tori around boson stars also possess distinctive morphology compared to the Kerr black hole [47,52]. The equilibrium tori in the Kerr spacetime are typically characterized by a cusp located at their inner edge with the exception of a small range of configurations limited to specific angular momenta of the disk [5,53]. ...
The effects of magnetic fields on accretion disks around compact objects are of high importance in the study of their general properties and dynamics. Here we analyze the influence of magnetic fields on thick accretion disks around rotating boson stars. We assume a uniform constant specific angular momentum distribution and a polytropic equation of state. The purely hydrodynamical thick disk solutions are extended to magnetized solutions by adding a toroidal magnetic field and then analyzed in terms of a magnetization parameter. We consider one-centered solutions as well as two-centered solutions and focus on retrograde tori, since they are more distinctive due to their unique properties. Our computed solutions indicate that strong magnetic fields influence the characteristics of thick disks around rotating boson stars and possibly effect their unique features.
... The unusual structure of COD around relativistic objects is not a prerogative of F/JNW; the uncomplete list of papers includes, e.g., [14][15][16][17][18][19][20][21][22][23][24]. As for the configurations with scalar fields, apart from F/JNW, the nonconnected SCO distributions have been demonstrated in the case of massive SF [23] and in case of nonlinear SFs with the monomial potential [10,24]. ...
... The works [11][12][13][14][15][16][17][18][19][20][21][22][23][24] deal with the geodesic particle motion; no additional particle interaction is introduced. In the present paper we focus on the nonconnected SCO distributions under assumptions that the massive particles interact with SF. ...
... (2) can be considered as the geodesics in the space-time with the conformal metric g μν ¼ ψ 2 g μν (ψ > 0). In the cases described by (17) and (20), for jξj ≪ 1, we have ξ ∼ κjϕj n ∼ κðjQj=rÞ n . ...
We study effects of the particles coupling with scalar field (SF) on the distribution of stable circular orbits (SCO) around the naked singularity described by the well-known Fisher-Janis-Newman-Winicour solution (F/JNW). The power-law and exponential models of the particle–SF interaction are analyzed. The focus is on the nonconnected SCO distributions. A method is used that facilitates numerical studies of the SCO regions in the case of the general static spherically symmetric metric. In case of F/JNW, we show that coupling between particles and SF can essentially complicate the topology of the SCO distributions. In particular, it can lead to new nonoverlapping SCO regions, which are separated by unstable orbits and/or by regions where the circular orbits do not exist.
... The unusual structure of COD around relativistic objects is not a prerogative of F/JNW; the uncomplete list of papers includes, e.g., [13][14][15][16][17][18][19][20][21][22][23]. As for the configurations with scalar fields, apart from F/JNW, the non-connected SCO distributions have been demonstrated in the case of massive SF [22] and in case of nonlinear SFs with the monomial potential [9,23]. ...
... The works [10][11][12][13][14][15][16][17][18][19][20][21][22][23] deal with the geodesic particle motion; no additional particle interaction is introduced. In the present paper we focus on the non-connected SCO distributions under assumptions that the massive particles interact with SF. ...
... Without loss of the generality, we assume Q > 0. We begin with some general analytical results concerning the sign ofL 2 (r) (i.e., where either SCO or UCO can exist) that follow directly from (16). ...
We study effects of the particles coupling with scalar field (SF) on the distribution of stable circular orbits (SCO) around the naked singularity described by the well-known Fisher-Janis-Newman-Winicour solution. The power-law and exponential models of the particle--SF interaction are analyzed. The focus is on the non-connected SCO distributions. We show that coupling between particles and SF can essentially complicate the topology of the SCO distributions. In particular, it can lead to new non-overlapping SCO regions, which are separated by unstable orbits and/or by regions where the circular orbits do not exist.
... GRMHD simulations with a similar setup are also used to address advection-dominated flows, the evolution of weakly magnetized disks, jet formation, and the differences between possible images of black holes (BHs) and boson stars (BSs) [7][8][9][10][11][12]. Outside the context of GRMHD simulations, Polish doughnuts are also used to address possible tori geometries around exotic spacetimes such as Kerr-de Sitter backgrounds, distorted static BHs, deformed compact objects, Kehagias-Sfetsos naked singularities, and BSs [13][14][15][16][17][18][19]. Although some models of doughnuts may include magnetic fields and nonconstant specific angular momentum distribution, the constant specific angular momentum case remains an important first step in this field of research, since in this case the torus solutions are marginally stable for Kerr BHs and hold similar topologies as the ones found for different specific angular momentum distributions [20,21]. ...
... As shown in [19], rotating BSs endowed with a static ring [38] are able to shelter tori presenting the so called static surfaces as well as compelling topologies (see also [18]). Similar results can be found for KBHsSH. ...
... One cusp connects the two centers, as typically happens for rotating BSs, but another cusp appears that connects the torus with the event horizon of the solution. It is also interesting to note that previously prograde doubled-centered tori were only found for BSs with winding number k > 3 [18]. In contrast, for KBHsSH, k ¼ 1 is sufficient to produce such configurations. ...
In this work we aim to investigate thick tori configurations around Kerr black holes with scalar hair (KBHsSH). For that goal, we provide a first approach using constant specific angular momentum non-self-gravitating Polish doughnuts. Through a series of examples, we show the feasibility of new topologies, such as double-centered tori with two cusps as well as similar structures as the ones found for rotating boson stars (BSs), namely, tori endowed with two centers and a single cusp. These KBHsSH solutions are also shown to possibly house static surfaces, associated with the static rings present in these spacetimes. Through this paper we highlight the differences between these fluid configurations when housed by some KBHsSH examples, standard Kerr black holes and rotating BSs.
... There are a number of papers on this subject including those, which use FJNW solution dealing with the linear SF [26,[28][29][30][31][32][33] and it would be interesting to study effects of nonlinearity. Several examples [32,[34][35][36][37][38][39][40][41] demonstrate occurrence of circular orbit distributions with several non-connected rings of SCO. This may be of particular interest as observational signs of differences from ordinary black holes, as well as the unusual form of the accretion disk images and/or their radiation properties [23,[29][30][31][42][43][44][45][46][47]. ...
We study stable circular orbits (SCO) around static spherically symmetric configuration of General Relativity with a non-linear scalar field (SF). The configurations are described by solutions of the Einstein-SF equations with monomial SF potential $V(\phi)=|\phi|^{2n}$, $n>2$, under the conditions of the asymptotic flatness and behavior of SF $\phi\sim 1/r$ at spatial infinity. We proved that under these conditions the solution exists and is uniquely defined by the configuration mass $M>0$ and scalar "charge" $Q$. The solutions and the space-time geodesics have been investigated numerically in the range $n\le40$, $|Q|\le 60$, $M\le60$. We focus on how nonlinearity of the field affects properties of SCO distributions (SCOD), which in turn affect topological form of the thin accretion disk around the configuration. Maps are presented showing the location of possible SCOD types for different $M,Q,n$. We found many differences from the Fisher-Janis-Newman-Winicour metric (FJNW) dealing with the linear SF, though basic qualitative properties of the configurations have much in common with the FJNW case. For some values of $n$, a topologically new SCOD type was discovered that is not available for the FJNW metric. All images of accretion disks have a dark spot in the center (mimicking an ordinary black hole), either because there is no SCO near the center or because of the strong deflection of photon trajectories near the singularity.
... Inspired by Wheeler's geon [25], BSs were first obtained half a century ago [26][27][28], and many of their aspects have been thereon extensively studied, as, e.g., spinning BS configurations [29][30][31][32][33][34][35], stability and formation [23,[36][37][38], or geodesic motion around them [39][40][41][42][43][44]. Boson stars could form through a process called gravitational cooling, where an initial cloud of scalar matter undergoes gravitational collapse and ejects matter and angular momentum through a series of cascade events until it settles into an equilibrium configuration. ...
... In [18], the authors find that the dark region resembling the shadow of a BH in the image due to a non-rotating BS is too small to fit the data from M87, but further investigation is required before dismissing the possibility of it being a rotating BS. Regarding fluid configurations around BSs, not only has research been done in the direction of disks [17][18][19]42] but also on tidal disruption events and disk formation [45,46]. ...
... In the context of GRMHD simulations, for example, they are used as initial condition to investigate advection-dominated flows [50], weakly magnetized disks [51], jet formation [52], similarities and differences between BH and BS images [17][18][19] and so on. The doughnuts are also a starting point for many analytical studies, among which we would like to highlight the ones regarding accretion disks sheltered by less-mainstream spacetimes, like Kerr-de Sitter backgrounds [53], Kerr black holes with scalar hair [54], distorted static BHs [55], deformed compact objects [56] and also BSs [42]. ...
We investigate polish doughnuts with a uniform constant specific angular momentum distribution in the space-times of rotating boson stars. In such space-times thick tori can exhibit unique features not present in Kerr space-times. For instance, in the context of retrograde tori, they may possess two centers connected or not by a cusp. Rotating boson stars also feature a static ring, neither present in Kerr space-times. This static ring consists of static orbits, where particles are at rest with respect to a zero angular momentum observer at infinity. Here we show that the presence of a static ring allows for an associated static surface of a retrograde thick torus, where inside the static surface the fluid moves in prograde direction. We classify the retrograde Polish doughnuts and present several specific examples.
