  Flat rotation curves follow from elongated Dark Matter distributions, as
shown by our earlier competitive fits to the SPARC database. Intending to probe
that distortion of the DM halo one needs observables not contained by the
galactic plane. Stellar streams are caused by tidal stretching of massive
substructures such as satellite dwarf galaxies, and would lie on a plane should
the DM-halo gravitational field be spherically symmetric. But if the field does
not display such spherical symmetry, stellar trajectories, as well as stellar
streams, should torsion out of the plane. This is where the torsion of the
stream can be of use: it is a local observable that measures the deviation from
planarity of a curve; thus, it quantifies how noncentral the gravitational
potential is. We have performed small simulations to confirm that indeed a
galactic central force produces negligible torsion, and quantified the torsion
for prolate haloes instead. Examining observational data, we select several
streams at large distance from the galactic center, as most promising for the
study, and by means of helicoidal fits extract their differential torsion. We
see that their torsion is much larger than expected for a central spherical
bulb alone, pointing to an elongated Milky Way halo.
