Ultrarelativistic heavy ion collisions performed at RHIC and LHC have been used to understand the thermodynamic and transport properties of QCD matter at high temperatures and densities. In this talk, the consequences of a nonzero bulk viscosity coefficient on heavy ion collision observables is investigated. I show that the agreement between our state-of-the-art hydrodynamic simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. This indicates that the bulk viscosity of QCD matter may not be as small as previously thought. I explain that the importance of bulk viscosity in simulations of heavy ion collisions is directly related to certain features of the initial state, such as the distance scales associated to energy density fluctuations.
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