Why do spiral galaxies twist the same way in cosmic filaments?

Using deep r-band images of 2,000+ galaxies in the Perseus-Pisces supercluster, astronomers measured how galaxy shapes correlate with their cosmic surroundings. Spirals show strong alignment signals in filaments—likely twisted by tidal forces—while ellipticals cluster near group centers with different alignment patterns. This local-universe result directly predicts contamination in upcoming dark matter experiments like Euclid and LSST.