Star formation is the mechanism which controls the structure and evolution of galaxies, the buildup of heavy elements in the universe with time, and which is responsible for the creation of the planetary environments in which life in the universe has become possible.

Formation of a young star

The Atacama Large Millimeter Array will be unique in its ability to detect the signature of protostellar collapse on solar-system size scales. We know that star formation involves gravitational collapse, but infall motions forming a new star have yet to be found. To observe unambiguous evidence for collapse, we require high spatial and velocity resolution (to map the velocity field across small structures) and high sensitivity (to take advantage of the spatial and velocity resolution). Furthermore, this must be available at a wavelength at which the collapsing object emits, and at which the surrounding material is transparent. Of current and planned instruments, only the Atacama Large Millimeter Array has these characteristics.

Star forming molecular cloud at optical wavelength	Star forming molecular cloud at radio wavelength

Further, the Atacama Large Millimeter Array will be ideal for studying the diversity of objects and physical processes involved in star formation. Its excellent mapping precision will allow astronomers to study the characteristics of parent molecular clouds from which stars form. Its sensitivity, angular and velocity resolution, and high frequency performance will allow the study of smaller structures--including protostellar fragments, outflows, and disks.