The collaborative research lead by Dr. Andersson (Universities Space Research Association), Dr. Jones (University of Minnesota), and Dr. Lazarian (University of Wisconsin, Madison) advances our ability to trace magnetic fields in the interstellar medium and molecular clouds through new multi-wavelength observations and theoretical modeling. It leads to a better understanding of the foregrounds to the cosmic microwave background (CMB) polarization through targeted observations of interstellar grain alignment and modeling based on the leading theoretical paradigm. The combined new quantitative effort addresses interstellar grain alignment mechanisms. A quantitative theory based on radiative alignment torques provides specific, testable predictions of the grain alignment as functions of the environment and grain characteristics. Observations, employing optical and near-infrared (NIR) polarimetry, directly probe the theoretical predictions of the variations of grain alignment efficiencies from the molecular cloud surfaces to the depths where (sub-)mm wave polarized emission is observed. Extensive modeling of the grain alignment, simulating the polarization arising from aligned grains, supports interpretations of the observations. A quantitative understanding of the alignment mechanism is important to understand the structure and strength of the magnetic field (through the geometry of the polarization vectors and the Chandrasekhar-Fermi method, respectively). The impact on related research ranges from models of star formation (through a reliable magnetic field tracing) to the physics of Early Universe (through a reliable separation of polarized dust foreground from the CMB polarized radiation) as well as a better understandinging micro-physics of interstellar dust grains. This project trains young researchers and graduate students in the acquisition, analysis and interpretation of the optical and NIR observations, and on computational models necessary for the study of astrophysical magnetic fields and the nature of interstellar polarization.
Studying how stars like the Sun form is an important area of research in astronomy. Since star formation is an ongoing process in the universe, there are always examples of objects in most every stage of star formation that we can observe. Of particular interest is the earliest phase of star formation, where a dense cloud of gas and dust shrinks down under the force of gravity to form a new star. In this early phase, magnetic fields can play a strong regulating role in the process by resisting the force of gravity. Measuring these magnetic fields, however, is very difficult. One technique uses the effect of dust grains in these dense clouds on the light traveling from a distant background star that passes through the dense cloud. The dust grains polarize the starlight, much like a pair of Polaroid sunglasses polarizes the light entering a human eye. This polarization effect is tied to the presence of a magnetic field, and is widely used to measure the magnetic field geometry in star forming regions. Our research sought to determine if this effect is really taking place for dust grains deep, deep down inside these dense clouds that are expected to form new stars in the very near future. Unfortunately, we found that starlight passing through a dense cloud of gas and dust is polarized by dust only in the outer periphery of the cloud. The dust deep inside, where the earliest stages of star formation is taking place, does not contribute to the observed polarization. This means astronomers will have to find some other technique to measure magnetic fields inside star forming clouds if they are to understand the role of magnetic fields in the star formation process.
