Tracing the structure of the interstellar magnetic field around the heliosphere using polarized starlight

Linearly polarized starlight is revealing the three-dimensional structure of the local interstellar magnetic field (ISMF) surrounding the heliosphere, and hitherto unknown aspects of the solar system's galactic environment. The polarization arises as starlight traverses a dichroic interstellar medium formed by aligned interstellar dust grains. An ongoing survey of the interstellar polarizations of nearby stars indicates that these data trace (at least) three magnetic field directions: the ISMF direction of the center of the arc of the IBEX Ribbon of energetic neutral atoms, an ISMF direction directed toward the inflow velocity vector of interstellar neutral gas into the heliosphere, and a new ISMF direction with an intriguing relation to the spatial kinematics of the interstellar cloud surrounding the heliosphere. A model that places the heliosphere in the rim of a superbubble shell explains both the IBEX ISMF direction and the newly discovered local ISMF direction, as well as the kinematics of local interstellar gas and the morphology of the local ISMF. The polarization filament appears to form where magnetic field lines carrying aligned interstellar dust grains are draping over the heliosphere. Two methods were developed to recover the very local ISMF direction from a survey of locally polarized starlight, both of which rely on the probability that a given position angle traces an arbitrary ISMF direction. Method 1 calculates the ISMF direction from polarization position angles by including low-probability data, while Method 2 recovers the ISMF direction using calculations of the highest probability values.