Event Horizon Telescope Observational Constraints on Dymnikova-Type Non-Singular Black Holes in Higher Dimensions

Abstract

Black holes are among the most compelling predictions of general relativity (GR) and are now strongly supported by observations from gravitational-wave detectors and the Event Horizon Telescope (EHT). While standard black hole solutions suffer from central singularities, regular black holes avoid this issue by introducing a nonsingular core. In this work, we extend the Dymnikova regular black hole to higher dimensions using a smooth matter distribution. The resulting spacetime features a de Sitter-like core and two horizons. We analyze photon motion and show that circular photon orbits remain unstable, giving rise to a well-defined black hole shadow. Our results indicate that the shadow size grows with the black hole scale but decreases slightly as the number of dimensions increases. We also investigate thermodynamic properties, including Hawking temperature and energy emission, and find a strong dependence on dimensionality. Finally, we compare our model with EHT observations to place constraints on the parameters and highlight potential observational signatures of higher-dimensional regular black holes.

Figures (5)

• Figure 1: The metric function $f(r)$ is examined across different parameter choices in higher-dimensional Dymnikova spacetimes. The left plot highlights how changing $r_0$ alters the profile while keeping $D=5$ and $r_s=1.88$ constant. The middle plot focuses on the influence of the dimensionality $D$, with $r_0=1.0$ and $r_s=1.88$. The right plot illustrates the impact of varying $r_s$ for fixed $r_0=1.0$ and $D=5$.
• Figure 2: The energy emission rate is investigated under different parameter choices in higher-dimensional Dymnikova spacetimes. The left panel shows the effect of varying $r_0$ while keeping $D=5$ and $r_s=1.88$ fixed. The middle panel illustrates the role of the dimensionality $D$, with $r_0=1.0$ and $r_s=1.88$. The right panel depicts the influence of changing $r_s$ for fixed $r_0=1.0$ and $D=5$.
• Figure 3: The black hole shadow is studied under different parameter choices in higher-dimensional Dymnikova spacetimes. The left panel shows how varying $r_0$ modifies the profile while keeping $D=5$ and $r_s=1.88$ fixed. The middle panel illustrates the effect of changing the dimensionality $D$, with $r_0=1.0$ and $r_s=1.88$. The right panel depicts the influence of varying $r_s$ for fixed $r_0=1.0$ and $D=5$.
• Figure 4: The black hole shadow radius (solid black line) is illustrated in higher-dimensional Dymnikova spacetimes. The left panel shows the effect of varying $r_0$ while keeping $D=5$ and $r_s=1.88$ fixed, whereas the right panel demonstrates the impact of changing $r_s$ for fixed $r_0=1.0$ and $D=5$. The blue and green shaded regions correspond to the EHT horizon-scale observations of Sgr A$^*$ and M87$^*$ at the $1\sigma$ level, while the light blue and light green areas represent the $2\sigma$ consistency ranges, respectively.
• Figure 5: The null geodesics and phase portrait in higher-dimensional Dymnikova spacetimes are analyzed. The left panel illustrates photon trajectories around the regular black hole, where the orange, blue, and gray curves correspond to different initial conditions, highlighting the distinction between capture, unstable circular orbits, scattering, respectively. The right panel shows the phase portrait of $\dot{r}$ versus $r$ for various choices of $r_0$ and $r_s$ with $D=5$. The magenta dot denotes the saddle (critical) point, which governs the stability properties of the photon sphere and separates the regions of bounded and unbounded motion.