Astronomers using the partially completed Modular Optical Telephoto Hyperspectral Robotic Array telescope in Chile detected 22 compact bow shocks in the eastern outskirts of the Helix Nebula, Nature reported.
Located 198.6 parsecs from Earth, the Helix Nebula contains gas expelled by the central white dwarf WD 2226-210. The arcs form where expanding stellar ejecta crash into the ambient interstellar medium at relative speeds of 80 to 90 kilometers per second.
Mapping the outer shocks
Observations taken in November 2025 captured Hydrogen-alpha emission using five operational mounts at the El Sauce Observatory. The recorded data equaled 20 minutes of exposure time on the planned 1,140-lens array, which uses Canon 400 millimeter telephoto lenses fitted with tiltable interference filters.
Across radial distances between 0.4 and 1.4 parsecs from the central star, the curvature radius of the shocks shrinks by roughly a factor of 100. Near the white dwarf, the structures appear thin and sharply defined, but they transition into fuzzy, patchy features further out.
Fragment disruption and velocities
Modeling indicates gas clumps moving eastward expanded at velocities between 35 and 45 kilometers per second, giving them a dynamical age of 20,000 to 30,000 years. That age predates the primary planetary nebula, which formed approximately 12,000 years ago.
Foci of parabolic fits to the shocks showed no corresponding line emission, indicating that the driving gas fragments remain largely neutral. The measured loss of shape coherence corresponds to an e-folding timescale of roughly 7,000 years, implying fragment disruption within 10,000 years.
MOTHRA's ultra-narrow interference filters measure emission across a velocity bandwidth of about 430 kilometers per second. The observatory captured circular sky offset patterns to model sky background before applying point spread function matching for continuum subtraction.
