Recent estimations of the Hubble parameter $H_0$ based on gravitational waves (GW) observations confirm the discrepancy between the value obtained from large scale and small scale observations, such as low red-shift supernovae (SN). In order to investigate the origin of this discrepancy we perform a combined analysis of the luminosity distance of SN and GW sources and reconstruct the velocity and density field, obtaining evidence of a local inhomogeneity with a density contrast of about $-0.048 \pm 0.003$, extending up to a red-shift of about $0.083\pm 0.005$. The dominant monopole effect of this inhomogeneity on the luminosity distance is proportional to the volume average of the density constrast inside the sphere of radius equal to the distance of the source, which is suppressed outside the inhomogeneity by the inverse cube of the distance. As a direct consequence, since most of the GW sources are located outside this inhomogeneity, they are excepted to be only negligibly affected by it, implying a value of $H_0$ in agreement with cosmic microwave background (CMB) observations, while most of the SN are inside the inhomogeneity, giving rise to the apparent discrepancy between the two different estimations.
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