Research Projects

Scientific rationale: The physical processes dictating the formation and evolution of molecular clouds and star formation in them are not fully understood. It is well established that stars form out of gravitationally collapsing, cold, and dense portions of molecular clouds. Suppose gravity had been the sole agent governing the entire star formation process; the star formation rate could have been substantially high, and all the molecular clouds would have been transformed into stars within a short time known as the free-fall time-scale (nearly 1 Myr for a typical molecular cloud). However, observations suggest the opposite: the star formation efficiency in our Milky Way Galaxy is inefficient, forming one star (with a mass equivalent to one solar mass) per year, and molecular clouds are found to live longer (nearly 10 Myr). This implies that some key agents must be slowing down the action of gravity. These include turbulence, magnetic fields, and stellar feedback. Among other parameters, it has been shown that magnetic fields are difficult to probe and measure. Hence, their role in the formation and evolution of clouds into stars remains poorly understood. We plan to resolve this problem using dust polarimetry and Zeeman splitting of neutral hydrogen lines. Telescope observations to be carried out: We use multi-wavelength (optical, near-infrared, and sub-millimeter) dust extinction and emission polarization observations to delineate the morphology and estimate the strengths of magnetic fields across the scales and densities of molecular clouds. The basic assumption is that unpolarized light, when it passes through aligned, non-spherical dust grains (with respect to magnetic fields), can get linearly polarized. The polarization direction can reveal the orientation of the magnetic field. We will also measure circularly polarized light from the neutral HI lines to directly measure the magnetic field strengths in the clouds. Objectives: One of the key objectives is to test the strong versus weak B- field model for a given single molecular cloud. Suppose magnetic fields are more vital and dominant than gravity and turbulence; we expect to probe well-organized B-field structure with respect to cloud structure and both mass-to-flux ratio criticality and the Alfvenic Mac number to be less than 1. On the contrary, the opposite result is anticipated when B-fields are weaker than turbulence. Significance of the research: Thanks to the advent of wide-band polarimeters and advancements in detector technology, which have enabled us to produce maps of B-field strength, mass-to-flux ratio, and Alfvénic Mac number rather than a single mean value for the entire region. This transformation enables us to understand the role of magnetic fields from large- to small-scale (or low-density to high-density) regions. From this, a clear distinction can be made between threshold densities where the magnetic field role would switch from important to weak or vice versa.

Multi-wavelength polarimetry, dust polarization, magnetic fields, gravity and turbulence, molecular clouds, Zeeman effect