Shadows and photon spheres with spherical accretions in the four-dimensional Gauss–Bonnet black holeXiao-Xiong Zeng, Hai-Qing Zhang and Hongbao ZhangEur. Phys. J. C, 80 9 (2020) 872DOI: https://doi.org/10.1140/epjc/s10052-020-08449-y