Is $d^*(2380)$ a compact hexaquark state?

The most fascinating dibaryon in the non-strange quark sector is $d^*(2380)$, which was reported by WASA-at-COSY Collaboration and confirmed by A2@MAMI Collaboration. The reported mass and width are $M\approx2.37$ GeV, $\Gamma\approx70$ MeV and the quantum numbers $IJ^P=03^+$. The structure of $d^*(2380)$ is still in controversy. In the present calculation, the powerful method in few-body system, Gaussian expansion method is employed to explore the structure of $d^*(2380)$ in the framework of constituent quark models without assuming the presupposed structure. The results show that the radius of $d^*(2380)$ is around 0.7 fm, a very compact object. Because of the compact structure, the color singlet-singlet component has a large overlap with the color octet-octet one, two colorless, large overlapped $\Delta$s dominate the state is possible.