Spirals, Tides, and M51

Spiral galaxies are undoubtedly one of the most beautiful structures in the universe. Yet, their simple elegance belies a complex nature. How do such structures not "wind up" and what causes them in the first place? The answers to these questions is a long standing challenge. Under one model, spiral structure is created by spiral density waves. In another, they are induced by tidal interactions. It is this approach that is explored in a new paper by Dobbs et al., accepted for publication in the Monthly Notices of the Royal Astronomical Society. Specifically, the authors attempted to use modeling of tidal forces to recreate the structure of the spiral arms on the grand design spiral, M51.(...)
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