Final Report Summary - PALS (The calm before the storm: Pre-stellar cores as Astrophysical Laboratories)
Stars like our Sun and planets like our Earth form within dense interstellar clouds, called pre-stellar cores, made out of gas and tiny dust particles. These clouds are very cold (-263 Celsius) and they are difficult to study, as they are dark and the emitting molecules are mainly frozen onto the dust, forming thick icy mantles around the dust particles. It is extremely important to study the physical and chemical structure of pre-stellar cores, as stellar system like our own are formed via the gravitational contraction of such objects. With PALs, we have been able to study in detail pre-stellar cores and their evolution toward stellar systems. Main results of PALs include: (i) the finding that pre-stellar cores are contracting in quasi-equilibrium and that previously well accepted models of cloud dynamical evolution do not work; (ii) the discovery of a shell of molecular material around the central pre-stellar core regions, including complex organic molecules which are important building blocks for pre-biotic molecules and life; (iii) a detailed treatment of gas-dust chemical processes during the evolution of pre-stellar cores, which follows the variation of the composition of ice mantles and surfaces with time and has allowed us to reproduce successfully the observed molecular shell surrounding the pre-stellar cores; (iv) the solution to the problem of protoplanetary disk formation following the contraction of magnetised pre-stellar cores, which we attribute to the disappearance of the very small dust grains (important charge carriers which follow the magnetic field and tend to remove angular momentum, thus preventing the formation of flattened structures within which future planets will form, i.e. protoplanetary disks); (v) the chemical evolution and consequent simulated observations of young protoplanetary disks, to guide observations which have been successfully carried out using the most powerful interferometer available in the world (ALMA, the Atacama Large Millimetre/sub-millimetre Array); (vi) the discovery that the main characteristics in the early stages of star formation found in nearby pre-stellar cores, are also present in objects embedded in very different environments. All this work has opened new research that is still going on and has seen important input from scientists experts in different fields, such as theoretical chemistry, experimental chemistry, plasma physics.