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

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 $gtrsim120,000$ AU. We find that in the ultra-cold outflow, the mass-loss rate (dM/dt) increases with radius, similar to its expansion velocity ($V$) - taking $Vpropto r$, we find $dM/dt propto r^{0.9-2.2}$. The mass in the ultra-cold outflow is $gtrsim3.3$ Msun, and the Boomerangs main-sequence progenitor mass is $gtrsim4$ Msun. Our high angular resolution ($sim$0.3) CO J=3-2 map shows the inner bipolar nebulas precise, highly-collimated shape, and a dense central waist of size (FWHM) $sim$1740 AU$times275$ AU. The molecular gas and the dust as seen in scattered light via optical HST imaging show a detailed correspondence. The waist shows a compact core in thermal dust emission at 0.87-3.3 mm, which harbors $(4-7)times10^{-4}$ Msun~of very large ($sim$mm-to-cm sized), cold ($sim20-30$ K) grains. The central waist (assuming its outer regions to be expanding) and fast bipolar outflow have expansion ages of $lesssim1925$ yr and $le1050$ yr: 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 Boomerangs primary was an RGB or early-AGB star, with the companion finally merging into the primarys core, and ejecting the primarys envelope that now forms the ultra-cold outflow.