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The Ophiuchus stellar stream is peculiar: (1) its length is short given theage of its constituent stars, and (2) several probable member stars that lieclose in both sky position and velocity have dispersions in these dimensionsthat far exceed those seen within the stream. The stream's proximity to theGalactic center suggests that the bar must have a significant influence on itsdynamical history: The triaxiality and time-dependence of the bar may generatechaotic orbits in the vicinity of the stream that can greatly affect itsmorphology. We explore this hypothesis with models of stream formation alongorbits consistent with Ophiuchus' properties in a Milky Way potential modelthat includes a rotating bar. We find that in all choices for the rotationparameters of the bar, orbits fit to the stream are strongly chaotic. Mockstreams generated along these orbits qualitatively match the observedproperties of the stream: because of chaos, stars stripped early generally formlow-density, high-dispersion "fans" leaving only the most recently disruptedmaterial detectable as a strong over-density. Our models predict that thereshould be more low-surface-brightness tidal debris than detected so far, likelywith a complex phase-space morphology. The existence of or lack of thesefeatures around the Ophiuchus stream would provide an interesting constraint onthe properties of the Milky Way bar and would help distinguish betweenformation scenarios for the stream. This is the first time that chaos has beenused to explain the properties of a stellar stream and is the firstdemonstration of the dynamical importance of chaos in the Galactic halo. Theexistence of long, thin streams around the Milky Way---presumably formed alongnon- or weakly-chaotic orbits---may represent only a subset of the totalpopulation of disrupted satellites.

Spending too much time at the Galactic bar: chaotic fanning of the Ophiuchus stream