Black-bounce spacetime and galactic rotation curves: from singularity resolution to observable gravitational effects

Abstract

The black-bounce spacetime provides a regularized modification of the Schwarzschild metric by introducing a free parameter $a$ that eliminates the central singularity while preserving the exterior geometry of a classical black hole. This work investigates the physical implications of this metric across three complementary observational windows. First, we examine the horizon structure and the transition between a regular black hole ($a < 2M$) and a traversable wormhole ($a > 2M$), offering a viable singularity-free alternative to classical black hole solutions. Second, we perform Solar System precision tests perihelion precession of Mercury, gravitational lensing, and the Shapiro time delay of radar signals demonstrating that the bounce parameter $a$ introduces small but measurable corrections relative to general relativity. Third, and for the first time, we apply the black-bounce metric to galactic dynamics by deriving the circular velocity field and fitting it to the observed rotation curve of NGC~7331. A four-component mass decomposition black-bounce central potential, Freeman exponential disc, Hernquist bulge, and a Navarro--Frenk--White dark matter halo yields $a = 1.035 \pm 0.119$~kpc , providing the first observational constraint on the bounce parameter from galaxy kinematics. Our results confirm that the black-bounce metric regularises the inner galactic core while remaining fully consistent with a standard dark matter halo at large radii, establishing this spacetime as a compelling testbed for singularity-free alternatives to classical black holes.