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The hypothesis that the late Universe is isotropic and homogeneous is adoptedby most cosmological studies. The expansion rate $H_0$ is thought to bespatially constant, while bulk flows are often presumed to be negligiblecompared to the Hubble expansion, even at local scales. Their effects on theredshift-distance conversion are hence usually ignored. Any deviation from thisconsensus can strongly bias the results of such studies and thus the importanceof testing these assumptions cannot be understated. Scaling relations of galaxyclusters can be effectively used for that. In previous works, we observedstrong anisotropies in cluster scaling relations, whose origins remainambiguous. By measuring many different cluster properties, several scalingrelations with different sensitivities can be built. Nearly independent testsof cosmic isotropy and bulk flows are then feasible. We make use of up to 570clusters with measured properties at X-ray, microwave, and infraredwavelengths, to construct 10 different cluster scaling relations (five of thempresented for the first time) and test the isotropy of the local Universe.Through rigorous tests, we ensure that our analysis is not prone to generallyknown systematic biases and X-ray absorption issues. By combining all availableinformation, we detect an apparent $9\%$ spatial variation in the local $H_0$between $(l,b)\sim({280^{\circ}}^{+35^{\circ}}_{-35^{\circ}},{-15^{\circ}}^{+20^{\circ}}_{-20^{\circ}})$and the rest of the sky. The observed anisotropy has a nearly dipole form.Using Monte Carlo simulations, we assess the statistical significance of theanisotropy to be $>5\sigma$. This result could also be attributed to a $\sim900$ km/s bulk flow which seems to extend out to at least $\sim 500$ Mpc. Thesetwo effects are indistinguishable until more high$-z$ clusters are observed byfuture all-sky surveys, such as eROSITA.

Cosmological implications of the anisotropy of ten galaxy cluster scaling relations