Stellar streams have long been treated as relatively smooth structures whose gaps, kinks and spurs could reveal invisible clumps of dark matter. Simulations of nearly 15,000 streams found that realistic Milky Way-sized galaxies can create many of the same irregularities without any dark matter subhalo encounters. Only about 70 simulated streams remained both free of off-track features and detectable density disturbances after five billion years, complicating efforts to identify dark matter from appearance alone. Long ribbons of stars loop around the Milky Way far beyond the galaxy’s familiar flat disk. Astronomers have hoped that disturbances in these stellar streams could expose something otherwise invisible: small clumps of dark matter. That possibility has made gaps, spurs, kinks and other irregularities in stellar streams especially valuable. A passing concentration of dark matter could gravitationally disturb the stars, leaving behind a recognizable scar. But those scars may have another source. A University of Washington study found that realistic galaxies can produce remarkably complicated stellar streams even without encounters with small dark matter clumps. A selection of virtual stellar …