Abstract
We study strong deflection gravitational lensing by a Lee-Wick ultracompact object. Its unique feature is a series of relativistic images inside its photon sphere, which are absent in the case of a black hole. We obtain its observables and estimate them for the supermassive black holes Sgr A* and M87* respectively in the Galactic center and in the center of M87. We find that the innermost relativistic image is a very promising signature according to its angular separation from the photon sphere and its considerable brightness. A preliminary bound on the UV scale of such an object is estimated based on the shadow of M87*.
Highlights
Compact object which is more massive than a neutron star but without the event horizon [25] or a compact quantum object which exists due to the quantum dynamics [26]
In the strong deflection gravitational lensing by a black hole, the deflection angle can become much bigger than unity, producing a set of relativistic images in the outside of and very close to its photon sphere [54] and forming an escape cone of light, known as “shadow”, inside the photon sphere [55]
We study the strong deflection gravitational lensing by the Lee-Wick ultracompact object and obtain its observables, including the apparent radius of the photon sphere as well as the angular separations and the brightness differences between the relativistic images
Summary
We focus on a Lee-Wick ultracompact object. It is based on a new local higher derivative theory of gravity without real poles [39,40,41,42,43], which is consistent with the Lee-Wick model [44,45,46]. A black hole solution to the theory was currently found and proved to be non-singular [47] Such a theory permits a spacetime solution without the event horizon and central singularity but with the photon sphere, which might be treated as the Lee-Wick ultracompact object. While thermodynamics [47] and strong deflection gravitational lensing [48] of the Lee-Wick black hole were investigated, it is still unknown about physical properties and observational signature of the Lee-Wick ultracompact object, which are critical for searching and distinguishing such a horizonless object. In light of successful direct imaging M87* by the Event Horizon Telescope (EHT) [7], we will concentrate on investigating the behavior of the Lee-Wick ultracompact object on electromagnetic waves, especially strong deflection gravitational lensing and its unique signature.
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