An improved model for star formation
Star formation, once thought to consist essentially of just the simple coalescence of material by gravity, actually occurs in a complex series of stages. As the gas and dust in giant molecular clouds come together into stars, circumstellar disks develop (possibly pre-planetary in nature), and later on dramatic outflowing jets appear. Key to initiating the process is the behavior of the gas. Although it has a finite temperature and hence a finite outward pressure, the pressure must be insufficient to support the gas against gravitational collapse. The subsequent cloud evolution also depends on the detailed density structure of the gas with a variety of different outcomes being possible, for example, fragmentation into smaller clouds. A key relationship is that between the temperature and density within the medium, and, as a result, the way the cloud radiates as the initial cooling dominance of molecular gas is overtaken by cooling from its...