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Register a new userRing-down gravitational waves and lensing observables: How far can a wormhole mimic those of a black hole?
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It has been argued that the recently detected ring-down gravity waveforms could be indicative only of the presence of light rings in a horizonless object, such as a surgical Schwarzschild wormhole, with the frequencies differing drastically from those of the horizon quasinormal mode frequencies $omega _{text{QNM}}$ at late times. While the possibility of such a horizonless alternative is novel by itself, we show by the example of Ellis-Bronnikov wormhole that the differences in $omega _{text{QNM}}$ in the eikonal limit (large $l$) need not be drastic. This result will be reached by exploiting the connection between $omega _{text{QNM}}$ and the Bozza strong field lensing parameters. We shall also show that the lensing observables of the Ellis-Bronnikov wormhole can also be very close to those of a black hole (say, SgrA$^{ast }$ hosted by our galaxy) of the same mass. This situation indicates that the ring-down frequencies and lensing observables of the Ellis-Bronnikov wormhole can remarkably mimic those of a black hole. The constraint on wormhole parameter $gamma $ imposed by experimental accuracy is briefly discussed. We also provide independent arguments supporting the stability of the Ellis-Bronnikov wormhole proven recently.
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Recent trend of research indicates that not only massive but also massless (asymptotic Newtonian mass zero) wormholes can reproduce post-merger initial ring-down gravitational waves characteristic of black hole horizon. In the massless case, it is the non-zero charge of other fields, equivalent to what we call here the Wheelerian mass, that is responsible for mimicking ring-down quasi-normal modes. In this paper, we enquire whether the same Wheelerian mass can reproduce black hole observables also in an altogether different experiment, viz., the strong field lensing. We examine two classes of massless wormholes, one in the Einstein-Maxwell-Dilaton (EMD) theory and the other in the Einstein-Minimally-coupled-Scalar field (EMS) theory. The observables such as the radius of the shadow, image separation and magnification of the corresponding Wheelerian masses are compared with those of a black hole (idealized SgrA* chosen for illustration) assuming that the three types of lenses share the same minimum impact parameter and distance from the observer. It turns out that, while the massless EMS wormholes can closely mimic the black hole in terms of strong field lensing observables, the EMD wormholes show considerable differences due to the presence of dilatonic charge. The conclusion is that masslessless alone is enough to closely mimic Schwarzschild black hole strong lensing observables in the EMS theory but not in the other, where extra parameters also influence those observables. The motion of timelike particles is briefly discussed for completeness.
We first advance a mathematical novelty that the three geometrically and topologically distinct objects mentioned in the title can be exactly obtained from the Jordan frame vacuum Brans I solution by a combination of coordinate transformations, trigonometric identities and complex Wick rotation. Next, we study their respective accretion properties using the Page-Thorne model which studies accretion properties exclusively for $rgeq r_{text{ms}}$ (the minimally stable radius of particle orbits), while the radii of singularity/ throat/ horizon $r<r_{text{ms}}$. Also, its Page-Thorne efficiency $epsilon$ is found to increase with decreasing $r_{text{ms}}$ and also yields $epsilon=0.0572$ for Schwarzschild black hole (SBH). But in the singular limit $rrightarrow r_{s}$ (radius of singularity), we have $epsilonrightarrow 1$ giving rise to $100 %$ efficiency in agreement with the efficiency of the naked singularity constructed in [10]. We show that the differential accretion luminosity $frac{dmathcal{L}_{infty}}{dln{r}}$ of Buchdahl naked singularity (BNS) is always substantially larger than that of SBH, while Eddington luminosity at infinity $L_{text{Edd}}^{infty}$ for BNS could be arbitrarily large at $rrightarrow r_{s}$ due to the scalar field $phi$ that is defined in $(r_{s}, infty)$. It is concluded that BNS accretion profiles can still be higher than those of regular objects in the universe.
Current ground-based gravitational wave detectors are tuned to capture the collision of compact objects such as stellar origin black holes and neutron stars; over 20 such events have been published to date. Theoretically, however, more exotic compact objects may exist, collisions of which should also generate copious gravitational waves. In this paper, we model the inspiral of a stellar mass black hole into a stable, non-spinning, traversable wormhole, and find a characteristic waveform -- an anti-chirp and/or burst -- as the black hole emerges, i.e., outspirals, into our region of the Universe. This novel waveform signature may be useful in searches for wormholes in future gravitational wave data or used to constrain possible wormhole geometries in our Universe.
Stable massless wormholes are theoretically interesting in their own right as well as for astrophysical applications, especially as galactic halo objects. Therefore, the study of gravitational lensing observables for such objects is of importance, and we do here by applying the parametric post-Newtonian method of Keeton and Petters to massless dyonic charged wormholes of the Einstein-Maxwell-Dilaton field theory and to the massless Ellis wormhole of the Einstein minimally coupled scalar field theory. The paper exemplifies how the lensing signatures of two different solutions belonging to two different theories could be qualitatively similar from the observational point of view. Quantitative differences appear depending on the parameter values. Surprisingly, there appears an unexpected divergence in the correction to differential time delay, which seems to call for a review of its original derivation.
The problem of bending and scattering of light rays passing outside from the entrance to a wormhole with zero gravitational mass is considered. The process of ray capture by a wormhole as well as the process of formation of a shadow when illuminated by a standard screen is investigated. These mechanisms are also compared to the case of motion of light rays in the vicinity of the Schwarzschild black hole.
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