Lensing and dynamics of ultracompact bosonic stars

Cunha, Pedro V. P.; Font, José A.; Herdeiro, Carlos; Radu, Eugen; Sanchis-Gual, N.; Zilhão, Miguel

doi:10.1103/physrevd.96.104040

Cited by 92 publications

(103 citation statements)

References 69 publications

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“…17 [87]. Mini boson stars provide another example as they can develop a light ring due to a central density peak, although sufficiently peaked configurations are only found in the unstable branch [88].…”

Section: B Boson Starsmentioning

confidence: 99%

On gravitational echoes from ultracompact exotic stars

Urbano

Veermäe

2019

J. Cosmol. Astropart. Phys.

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At the dawn of a golden age for gravitational wave astronomy, we must leave no stone unturned in our quest for new phenomena beyond our current understanding of General Relativity (GR), particle physics and nuclear physics. In this paper we discuss gravitational echoes from ultracompact stars. We restrict our analysis to exact solutions of Einstein field equations in GR that are supported by physically motivated equations of state (EoS), and in particular we impose the constraint of causality. Our main conclusion is that ultracompact objects supported by physical EoS are not able to generate gravitational echoes like those that characterize the relaxation phase of a putative black hole mimicker. Nevertheless, we identify a class of physical exotic objects that are compact enough to accommodate the presence of an external unstable light ring, thus opening the possibility of trapping gravitational radiation and affecting the ringdown phase of a merger event. Most importantly, we show that once rotation is included these stars -contrary to what usually expected for ultracompact objects -are not plagued by any ergoregion instability. We extend our analysis for arbitrary values of angular velocity up to the Keplerian limit, and we comment about potential signals relevant for gravitational wave interferometers. 1 arXiv:1810.07137v2 [gr-qc]

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Section: B Boson Starsmentioning

confidence: 99%

On gravitational echoes from ultracompact exotic stars

Urbano

Veermäe

2019

J. Cosmol. Astropart. Phys.

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“…Finally, we build the complete image of the shadow along with the relativistic images from the ZV solution Figs. 9 -11 just like it was done in [3][4][5][6]. From the observation point r O = 5M , a set of geodesics in different directions on the celestial sphere is launched in stereographic coordinates (X, Y ) (4.8) and tracked to which part of the sphere r = 30M colored with four colors will fall into the geodesic.…”

Section: Shadowmentioning

confidence: 99%

Photon trapping in static axially symmetric spacetime

Gal’tsov

Kobialko

2019

Phys. Rev. D

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Recently, several new characteristics have been introduced to describe null geodesic structure of strong gravitational field, such as photon regions, transversely trapping surfaces and some generalizations. They give an alternative and concise way to describe lensing and shadow features of compact objects with strong gravitational field without recurring to complete integration of the geodesic equations. Here we test this construction in the case of the Weyl metrics when geodesic equations are non-separable, and thus can not be integrated analytically, while the above characteristic surfaces and regions can be described in a closed form. We develop further our formalism for a class of static axially symmetric spacetimes introducing more detailed specification of transversely trapping surfaces in terms of their principal curvatures. Surprisingly, we find in the static case without spherical symmetry certain features, such as photon regions, previously known in the Kerr space. These photon regions can be regarded as photon spheres, "thickened" due to oblateness of the metric.including the dilaton field [34]).Meanwhile, in the stationary spacetimes photon surfaces generically do not exist, being, in some sense, disintegrated by rotation. The Taub-NUT metric, though belongs to this class, is an exception, whose existence is explained by local SO(3) symmetry which is preserved. In the Kerr metric the circular photon orbits exist in the equatorial plane [35]. Non-equatorial orbits with constant Boyer-Lindquist radii no longer belong to any plane, but lie on the surface of a sphere instead ("spherical photon orbits" [36]). But such surfaces are not photon spheres, which by definition should be densely filled. In the Kerr case every spherical orbit corresponds to certain value of the impact parameter defined as ratio of the angular momentum to the energy. Altogether spherical orbits now will a three-dimensional photon region (PR) [37][38][39], which can be regarded as "thickened" photon sphere. Note that the closed photon orbits may exist in more general spacetimes in which case the name of fundamental or/and spheroidal photon orbits was suggested [40][41][42].More general trapping surfaces, proposed in [43] and further studied in [44], were called transversely trapping surfaces (TTS). In Schwarzschild case TTS are the spheres with the radii r ≤ 3M . These are defined as surfaces such that initially tangent photons either remain in them or move inward; these do exist in Kerr and more general stationary axially symmetric metrics.The totality of TTSs form a three-dimensional region (TTR), which apparently will be invisible if one looks at the Schwarzschild black hole illuminated from behind. Further generalizations suggested in [44] include partial TTS (PTTS) which are non-closed surfaces (contrary to the definition in [43]) of the shape of a spherical cap. Finally, it is reasonable to introduce anti-TTS and PTTS (abbreviated as ATTS and APPTS, the corresponding regions -TTR and PTTR respoctively) replacing inward to outwa...

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“…To numerically evolve the scalar field equations in our prescribed metric background we employ the code presented in Refs. [29,34], which makes use of the Ein-steinToolkit infrastructure [35][36][37] with the Carpet package [38,39] for mesh-refinement capabilities. We employ the method-of-lines, where spatial derivatives are approximated by fourth-order finite difference stencils, and we use the fourth-order Runge-Kutta scheme for the time integration.…”

Section: Numerical Procedures and Convergence Analysismentioning

confidence: 99%

“…To numerically evolve the scalar field, we employ the code presented in Refs. [29,34], which makes use of the EinsteinToolkit infrastructure [35][36][37] with the Carpet package [38,39]. We project the scalar field onto scalar harmonics, Φ = lm Φ l,m Y lm .…”

mentioning

confidence: 99%

Physics of black hole binaries: Geodesics, relaxation modes, and energy extraction

et al. 2019

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Black holes are the simplest macroscopic objects, and provide unique tests of General Relativity. They have been compared to the Hydrogen atom in quantum mechanics. Here, we establish a few facts about the simplest systems bound by gravity: black hole binaries. We provide strong evidence for the existence of "global" photosurfaces surrounding the binary, and of binary quasinormal modes leading to exponential decay of massless fields when the binary spacetime is slightly perturbed. These two properties go hand in hand, as they did for isolated black holes. The binary quasinormal modes have high quality factor and may be prone to resonant excitations. Finally, we show that energy extraction from binaries is generic and we find evidence of a new mechanism -akin to the Fermi acceleration process -whereby the binary transfers energy to its surroundings in a cascading process. The mechanism is conjectured to work when the individual components spin, or are made of compact stars.

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Lensing and dynamics of ultracompact bosonic stars

Cited by 92 publications

References 69 publications

On gravitational echoes from ultracompact exotic stars

On gravitational echoes from ultracompact exotic stars

Photon trapping in static axially symmetric spacetime

Physics of black hole binaries: Geodesics, relaxation modes, and energy extraction

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