Context. Even though turbulent motions are found everywherein astrophysical systems, the origin of this turbulence is poorlyunderstood. When cosmic structures form, they grow in mass viaaccretion from their surrounding environment. Aims. We propose that accretion is able to drive internalturbulent motions in a wide range of astrophysical objects and studythis process in the case of galaxies, molecular clouds, andprotoplanetary disks. Methods. We use a combination of numerical simulations andanalytical arguments to predict the level of turbulence as a functionof the accretion rate, the dissipation scale, and the density contrast,and compare our models with observational data. Results. We find that in Milky Way type galaxies the observedlevel of turbulence in the interstellar medium can be explained byaccretion, provided that the galaxies gain mass at a rate comparable tothe rate at which they form stars. This process is particularlyrelevant in the extended outer disks beyond the star-forming radius.For it to drive turbulence in dwarf galaxies, the accretion rate needsto exceed the star formation rate by a large factor, so we expect othersources to dominate. We also calculate the rate at which molecularclouds grow in mass when they build up from the atomic component of thegalactic gas and find that their internal turbulence is likely to bedriven by accretion as well. It is the very process of cloud formationthat excites turbulent motions on small scales by establishing theturbulent cascade. In the case of TTauri disks, we show thataccretion can drive subsonic turbulence if the rate at which gas fallsonto the disk is comparable to the rate at which disk material accretesonto the central star. This also explains the observed relation ofaccretion rate and stellar mass, .The efficiency required to convert infall motion into turbulence is a few percent in all three cases. Conclusions. We conclude that accretion-driven turbulence is auniversal concept with far-reaching implications for a wide range ofastrophysical objects. Key words: accretion, accretion disks - turbulence - ISM:kinematics and dynamics - galaxies: kinematic and dynamics - planetarysystems: protoplanetary disks - galaxies: ISM
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