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Supermassive black holes (BH) accrete gas from their surroundings andcoalesce with companions during galaxy mergers, and both processes change theBH mass and spin. By means of high-resolution hydrodynamical simulations ofgalaxies, either idealised or embedded within the cosmic web, we explore theeffects of interstellar gas dynamics and external perturbations on BH spinevolution. All these physical quantities were evolved on-the-fly in aself-consistent manner. We use a `maximal' model to describe the turbulenceinduced by stellar feedback to highlight its impact on the angular momentum ofthe gas accreted by the BH. Periods of intense star formation are followed byphases where stellar feedback drives large-scale outflows and hot bubbles. Wefind that BH accretion is synchronised with star formation, as only when gas iscold and dense do both processes take place. During such periods, gas motion isdominated by consistent rotation. On the other hand, when stellar feedbackbecomes substantial, turbulent motion randomises gas angular momentum. HoweverBH accretion is strongly suppressed in that case, as cold and dense gas islacking. In our cosmological simulation, at very early times (z>6), thegalactic disc has not yet settled and no preferred direction exists for theangular momentum of the accreted gas, so the BH spin remains low. As the gassettles into a disc (6>z>3), the BH spin then rapidly reaches its maximalvalue. At lower redshifts (z<3), even when galaxy mergers flip the direction ofthe angular momentum of the accreted gas, causing it to counter-rotate, the BHspin magnitude only decreases modestly and temporarily. Should this be atypical evolution scenario for BH, it potentially has dramatic consequencesregarding their origin and assembly, as accretion on maximally spinning BHembedded in thin Shakura-Sunyaev disc is significantly reduced.

Black hole evolution: II. Spinning black holes in a supernova-driven turbulent interstellar medium