A cork of the rational surface with the second Betti number 9

We provide the first explicit example of a cork of ${\mathbf{C}\mathbf{P}}^2\mathrm{\#}8\overline{{\mathbf{C}\mathbf{P}}^2}$. This result gives the current smallest second Betti number of a standard simply-connected closed $4$-manifold for which an explicit cork has been found.