Stars are formed deep within giant molecular clouds in the galaxy, shrouding star formation in a fundamental yet unsolved mystery. It is a process that spans magnitudes in scale and is strongly coupled to the cloud's dynamics. The cloud is influenced by gravity, the interstellar magnetic field, supersonic turbulence, and mechanical and radiative feedback from the newborn stars themselves. The primary challenge to both theorists and observers is to determine the role each plays in the star formation process as these relate to the fraction of a cloud's mass converted into stars, the formation of massive stars and young stellar clusters, the distribution of angular momentum, and the quenching of star formation.
With its sensitivity to point sources and low surface brightness emission coupled with its imaging array instruments in the 1-3mm bands, the LMT can make significant contributions to this effort by measuring both the large scale low-density envelopes of giant molecular clouds and the high density cores from which stars and clusters condense.
Magneto-Turbulence in Molecular Clouds
Turbulent gas flows and the magnetic properties involved are key to regulating star formation and configuring the mass distribution of cores within them. By studying the molecular line emission of giant molecular clouds, measurements made by the LMT can assess the conditions in which the turbulent energy spectrum departs from the norm, which may signal zones of energy dissipation or injection, and may also help in determining the role of the magnetic fields.
Properties of Protostellar and Protocluster Cores
The protostellar and protocluster cores that emerge within the cloud are the precise sites of star formation. These cores strongly radiate in the 1mm band from cold dust within them. Imaging the thermal emission from dust grains over the extent of a molecular cloud using the LMT's millimeter-wavelength cameras provides a direct census of active or potential sites of star formation. The emission can be used to derive radial profiles of density for individual cores that can be compared to theoretical predictions and compile the core mass distribution function. Insight to the star formation process is further revealed by observations that probe the chemistry and kinematics of dense gas, as these trace the initial conditions prior to protostellar collapse.
The gravitational collapse of dense rotating cores within a molecular cloud results in the creation of a central protostar surrounded by a flattened spinning disk of gaseous material. In this accretion disk, mass is transported inward toward the star and angular momentum is transported outward. Eventually, around the time newly formed planets inhibit further growth of the star, the disk moves into a phase known as a debris disk, where it resembles something not so different from our own asteroid belt, with lots of dust and planetismals.
The accretion phase for low mass protostars that will become sun-like stars is intriguing, as it is always accompanied by the simultaneous presence of a high velocity ejection of material into bipolar jets that emerge perpendicular to the plane of the disk. Although we know that accretion disks and jets of expelled material are always seen together, exactly how this pairing happens is a mystery. It is possible to solve this mystery by further exploring both the intersection of the disk and the star, where the jets are probably formed, and the innermost part of the disk, which spinning rapidly and has a magnetic field.
Simulated observation of a protoplanetary disk. Generated with AzTEC operating at 1.1 mm on the LMT. The inner-hole could be created by the processes that sweep up material during the aggregation of planetesimals and early formation of planets.