The outflow of the Boomerang Nebula: The coldest object in the Universe

Abstract

The Boomerang Nebula is a preplanetary nebula with a massive and fast outflow. The gas in the outflow is seen as absorption against the cosmic microwave back- ground, making it the coldest known naturally occurring object in the Universe. Like an interstellar refrigerator, the outflow cools itself adiabatically. Old obser- vations with Swedish-ESO Submillimetre Telescope (SEST) were consistent with a constant-velocity outflow, but more recent observations, with Atacama Large Mil- limeter/submillimeter Array (ALMA), pointed to a model with an outflow velocity which varies radially. This thesis aims to reproduce the ALMA observations by considering two different scenarios, a scenario with an explosive event in which the material was ejected with a range of velocities and a scenario with an outflow with a time variable expansion velocity. The best-fit models for both scenarios produce similar spectra on the large scale, as the Boomerang Nebula in a larger region, but have difficulties matching the spectra along the line of sight through the center of the shell. The models that fit the data the best are similar too each other. The thesis also shows a model with a larger shell size than observed, that provides a good fit to the observations. While it is outside the scope of this thesis, it serves as a clue for future analysis of the Boomerang Nebula.