Time-delayย
theoretical predictions
Time-delayย
theoretical predictions
Here we show some results of applying our methodology to different spherical space-times:
Black Bounce (BB) space-time from which it results:
Einstein-Maxwell-dilaton-axion (EMDA) space-time. Therefore, to bring the EMDA metric in the desired form, we define
Scalar-Vector-Tensor Gravity (STVG) spherically symmetric space-time. Therefore, to bring the STVG metric in the desired form, we define
We computed the photon propagation time for the STVG model in order to assess differences from the Schwarzschild case and to check for the appearance of peculiar features that arise in the propagation delay for each model.ย
Figure: Differences in seconds from the Schwarzschild BH of the propagation delay in the BB (green lines, left panels), STVG (purple lines, center panels), and EMDA (blue lines, right panels) models, respectively, numerically computed with our code for a central object of ๐ = 4 million ๐โ and for the orbiting object Toy 1 having semi-major axis a = 175.4 AU, eccentricity e = 0.8, and period T = 1.1615 yr. Our calculation is particularized for three inclinations of ๐ = 0 (top panels), ๐ = 30 (center panels) and ๐ = 60 (bottom panels) degrees and over two and a half orbital periods (starting from apocenter where the relativistic orbital phase is ๐rel = ๐ to ๐rel = 6 ๐). Coloured solid lines correspond to increasingly higher deviations from the Schwarzschild limit obtained for different values of the theory parameter in their range of interest, as reported in the color bars and on the plotted labels.
In the Figure, the profiles would thus represent the possible amplitudes of the timing residuals obtained when fitting a Schwarzschild model to the TOA data for a pulsar that orbits one of the possible alternatives to the Schwarzschild black hole considered here. A notable feature from our profiles is that for edge-on orbits case, we always find an abrupt change in the propagation time when the pulsar is at superior conjunction due to the strong curvature of photon paths to go from the emitter to the observer and to the strong impact of the Shapiro delay for such photons. Indeed, this effect is not present for inclined orbits (for which superior conjunction is never realized). Furthermore, the departure between the different profiles from the Schwarzschild propagation time exhibits a secular increment due to the increase in the orbital precession as a result of a change in the underlying space-time geometry, which leads to an increasing departure of the spatial position along the orbit from where the photon starts. Finally, all the mentioned effects, have an amplitude that depends on the value of the theory parameter and on the orbital properties of the object at hand. Such departures in the photon propagation time, expressed in seconds, can span several orders of magnitude when particularized for the SMBH at the center of the MW. Moreover, the same object orbiting different space-time geometries generates different propagation delay profiles, not only in terms of amplitude but also of functional dependence on the orbital phase, presenting peculiar features that can provide an efficient way to identify the underlying theory of gravity.
For this research, Riccardo Della Monica got the Lluรญs Bel (SEGRE) award for the best presentation at the Spanish and Portuguese Relativity Meeting 2023.