Gas tips a young star’s rings and shreds an old star’s remains
ALMA observations made a gas streamer feeding GW Orionis the leading explanation for its tilted rings. MOTHRA’s first calibration image caught clumps from the Helix Nebula breaking apart in interstellar gas, revealing matter flows at opposite ends of stellar life.
Science··Midday
A gas streamer into GW Orionis tips its rings
An ALMA study led by Maria Galloway-Sprietsma of the University of Florida reported in a peer-reviewed Astronomical Journal paper a gas streamer 0.2 light-years long feeding the triple star system GW Orionis, about 1,300 light-years away in Orion. Because molecular hydrogen is invisible at radio wavelengths, the team traced the streamer through carbon monoxide. The three dust rings begin 44, 187 and 340 astronomical units from the tight triple, and the angle at which the streamer strikes the disk matches the tilt of the outer ring. The paper's best-fit trajectory shows the streamer meeting the disk at the outermost dust ring, with its angular-momentum vector aligned to that outer ring within about 3 degrees and misaligned from the innermost ring by about 32 degrees. The researchers say the streamer probably did most of the tipping in the past, when its angular momentum exceeded the disk's, displacing an unseen giant planet as the favoured explanation; the streamer mass estimated from 13CO is about 1.6 Jupiter masses.[1]
Bow shocks fragment in the Helix's outer halo
A team led by Yale University's Pieter van Dokkum, while calibrating the new MOTHRA array at Chile's El Sauce Observatory, caught 22 complete or partial bow shocks in the faint outer halo of the Helix Nebula 650 light-years away; the finding appears in a peer-reviewed Nature paper. The arcs form in H-alpha where clumps of gas thrown off by the dying star plough into the interstellar medium: sharp and thin near the star, smaller and more fragmented farther out. The bright ring of the Helix is 5.7 light-years across at its outer edge, and the halo lies beyond it. Roberto Abraham of the University of Toronto said the bow-shaped network stood out immediately in that first image. The team estimates that ejected material survives about 10,000 years in the interstellar medium before it is fully shredded and absorbed; the Helix was chosen only as a convenient calibration target.[2]
MOTHRA will hunt faint gas across a wider field
When complete, MOTHRA will carry 1,140 telephoto lenses to search for faint gas in the Milky Way; the Helix detection is a first result from calibrating the partially built array. The Nature paper reports that the radius of curvature falls by a factor of roughly 100 over 0.4 to 1.4 parsecs from the central star, with a morphological shift from thin, well-defined bows to fuzzy, patchy structures interpreted as progressive stripping of stellar debris into the interstellar medium. Astronomers had not previously watched this hand-off from stellar ejecta to diffuse interstellar gas at this clarity. The GW Orionis streamer shapes disk alignment in a young triple system, while the Helix bows show the final assimilation step for clumps from an old star, so matter flows at opposite ends of stellar life become visible in the same physical language.[2], [1]
