  In 1981, the idea of a superwind that ends the life of cool giant stars was
proposed. Extreme OH/IR-stars develop superwinds with the highest mass-loss
rates known so far, up to a few 10^(-4) Msun/yr, informing our understanding of
the maximum mass-loss rate achieved during the Asymptotic Giant Branch (AGB)
phase. A condundrum arises whereby the observationally determined duration of
the superwind phase is too short for these stars to become white dwarfs. Here,
we report on the detection of spiral structures around two cornerstone extreme
OH/IR-stars, OH26.5+0.6 and OH30.1-0.7, identifying them as wide binary
systems. Hydrodynamical simulations show that the companion's gravitational
attraction creates an equatorial density enhancement mimicking a short extreme
superwind phase, thereby solving the decades-old conundrum. This discovery
restricts the maximum mass-loss rate of AGB stars around the single-scattering
radiation-pressure limit of a few 10^(-5) Msun/yr. This brings about crucial
implications for nucleosynthetic yields, planet survival, and the wind-driving
mechanism.
