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[133.01] Milky Way's Structure: Theory

D. F. Bartlett (University of Colorado)

The cover of the August issue of the Astronomical Journal is stunningly simple. The basic structure of the Milky Way appears as a central bar surrounded by four evenly-spaced logarithmic spirals. (Vallée 2005). Modern density wave theory can accommodate such spirals, but only by using arbitrary functions of time (Bertin 2000).

Perhaps the problem is Newton's gravitational law itself. With or without dark matter, this law allows the potential to have only two kinds of extrema: dimples and saddle points. In contrast, the proposed sinusoidal potential also permits potential maxima or pimples. (In the sinusoidal potential \phi(r)=-(GM/r) cos(k_o r) where k_o = 2 \pi/\lambda_o and the universal 'wavelength' \lambda_o is 425 pc (Bartlett 2004).

I will show how the sinusoidal potential permits the spiral structure of the Galaxy to be stable. Deep ridges in the radial direction confine stars to circular orbits. A broad potential maximum in the z-direction suppresses the normally deep minimum at z=0 caused by matter in the local disk. Alternating minima and maxima in the \phi-direction give spirals that are keyed to the central bar.

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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.