Bulk Flow Motion Detection in the Local Universe with Pantheon+ Type Ia Supernovae

The bulk flow in the Local Universe is a collective phenomenon due to the peculiar motions of matter structures, which, instead of moving in random directions, appears to follow an approximate dipole velocity flow. We apply a directional analysis to investigate, through the Hubble-Lema\^tre diagram, the angular dependence of the Hubble constant H₀ of a sample of Type Ia Supernovae from the Pantheon+ catalog in the Local Universe (0. 015 z 0. 06). We perform a directional analysis that reveals a statistically significant dipole variation of H₀, at more than 99. 9\% confidence level, showing that matter structures follow a dipole bulk flow motion towards (l, b) = (326. ¹ 11. ², 27. ⁸ 11. ²), close to the Shapley supercluster (l₀. ₆ₒ₇₀₏₋₄ₘ, b₀. ₆ₒ₇₀₏₋₄ₘ) = (311. ⁵, 32. ³), with velocity 132. 14 109. 3 km s^-1 at the effective distance 102. 83 10. 2~Mpc. Interestingly, the antipodal direction of this dipole points close to the Dipole Repeller structure. Our analyses confirm that the gravitational dipole system Shapley-Dipole Repeller explains well the observed bulk flow velocity field in the Local Universe. Furthermore, we performed robustness tests that support our results. Additionally, our approach provides a measurement of the Hubble constant H₀ = 70. 39 1. 4~km s^-1 Mpc^{-1}, at the effective distance 102. 8~Mpc, z 0. 025. Note that this value was obtained using the first order approximation of the Hubble law because our methodology is model-independent. If one assumes, for instance, cosmography at second order with the CDM value q₀ = -0. 55, which is a model-dependent hypothesis, then H₀ = 72. 6 1. 5 km s^-1 Mpc^-1, but our results: bulk flow velocity, dipole direction and its statistical significance remain the same.