2017ApJ...841..110S

Our Cycle 0 ALMA observations confirmed that the Boomerang Nebula is the coldest known object in the universe, with a massive high-speed outflow that has cooled significantly below the cosmic background temperature. Our new CO 1-0 data reveal heretofore unseen distant regions of this ultra-cold outflow, out to >=120,000 au. We find that in the ultra-cold outflow, the mass-loss rate ({dot}M) increases with radius, similar to its expansion velocity (V)-taking V∝r, we find {dot}M∝r^0.9–2.2. The mass in the ultra-cold outflow is 3.3M_☉, and the Boomerang's main-sequence progenitor mass is 4M_☉. Our high angular resolution (∼0′′ / . 3) CO J = 3-2 map shows the inner bipolar nebula's precise, highly collimated shape, and a dense central waist of size (FWHM) ∼1740 au x 275 au. The molecular gas and the dust as seen in scattered light via optical Hubble Space Telescope imaging show a detailed correspondence. The waist shows a compact core in thermal dust emission at 0.87-3.3 mm, which harbors (4–7)×10^–4M_☉ of very large (∼millimeter-to-centimeter sized), cold (∼20–30 K) grains. The central waist (assuming its outer regions to be expanding) and fast bipolar outflow have expansion ages of 1925 years and 1050 years: the "jet-lag" (i.e., torus age minus the fast-outflow age) in the Boomerang supports models in which the primary star interacts directly with a binary companion. We argue that this interaction resulted in a common-envelope configuration, while the Boomerang's primary was an RGB or early-AGB star, with the companion finally merging into the primary's core, and ejecting the primary's envelope that now forms the ultra-cold outflow.