Slope of Magnetic Field–Density Relation as an Indicator of Magnetic Dominance

Abstract The electromagnetic field is a fundamental force in nature that regulates the formation of stars in the Universe. Despite decades of efforts, a reliable assessment of the importance of the magnetic fields in star formation relations remains missing. In star formation research, our acknowledgment of the importance of magnetic fields is best summarized by the R. M. Crutcher et al. B – ρ relation, log B ( ρ ) / Gauss = − 5 , if ρ ≲ 10 − 20 g cm − 3 2 3 · log ρ + log ρ 0 , if ρ ≳ 10 − 20 g cm − 3 , whose interpretation remains controversial. The relation is either interpreted as proof of the importance of a magnetic field in gravitational collapse or as the result of self-similar collapse where the role of the magnetic field is secondary to gravity. Using simulations, we find a fundamental relation, M A – k B − ρ (the slope of the B – ρ relation): M A M A , c = k B − ρ K ≈ M A 7.5 ≈ k B − ρ 1.7 ± 0.15 . <jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" orientation="portrait" position="float" xlink:href="apjad8b4dueqn2.gif" xlink:type="simple"