The Coldest Place in the Universe: Probing the Ultra-cold Outflow and Dusty Disk in the Boomerang Nebula

Journal article, 2017

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 greater than or similar to 120,000 au. We find that in the ultra-cold outflow, the mass-loss rate (M.) increases with radius, similar to its expansion velocity (V)-taking V alpha r, we find M alpha r(0.9-2.2). The mass in the ultra-cold outflow is greater than or similar to 3.3 M-circle dot, and the Boomerang's main-sequence progenitor mass is greater than or similar to 4 M-circle dot. Our high angular resolution (similar to 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) similar to 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) x 10(-4) M-circle dot of very large (similar to millimeter-to-centimeter sized), cold (similar to 20-30 K) grains. The central waist (assuming its outer regions to be expanding) and fast bipolar outflow have expansion ages of less than or similar to 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.