  When subcritical shear flows transition to turbulence, laminar and turbulent
flow often coexists in space, giving rise to turbulent-laminar patterns. Most
prominent are regular stripe patterns with large-scale periodicity and oblique
orientation. Oblique stripes are a robust phenomenon, observed in experiments
and flow simulations, yet their origin remains unclear. We demonstrate the
existence of an invariant equilibrium solution of the fully nonlinear 3D
Navier-Stokes equations that resembles the oblique pattern of turbulent-laminar
stripes in plane Couette flow. We uncover the origin of the stripe equilibrium
and show how it emerges from the well-studied Nagata equilibrium via two
successive symmetry-breaking bifurcations.
