Albert Bosma and Vera Rubin, et al, independently discovered that objects in the galactic disks of spiral galaxies did not comply with Kepler's laws of planetary motion, since their rotational velocities did not diminish with radial distance, but Rubin's work predated Bosma's by more than three years.
However, it was never formally established that the empirical laws of planetary motion should apply to spiral galaxies: this was simply presumed.
As Newton showed in his Principia, the accuracy of Kepler's equations is dependent on orbitals that contain nearly zero mass (the Sun contains 99.86% of total Solar system mass) so as not to perturb each other's orbits. The disks of spiral galaxies contain a relatively large percentage of total galactic mass; peripheral disk objects primarily interact with neighboring peer masses - they are self-gravitating. The motions of spiral galaxies can be generally described as rotating thin disks. Please see: Feng & Gallo, (2011), "Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies",
More precise measurements of 240 discrete Milky Way halo objects' rotational velocities (including globular clusters, satellite galaxies and individual stars) physically constrains the potential location of any dark matter halo. Please see: G. Battaglia et al, (2005), "The radial velocity dispersion profile of the Galactic halo: Constraining the density profile of the dark halo of the Milky Way", http://arxiv.org/abs/astro-ph/0506102
While the disks of spiral galaxies do not comply with Keplerian rotational curves, this same data indicates that the rotational velocities of halo objects DO diminish as a function of their radial distance and that each independently orbit the distant galactic disk "like planets in the Solar system," placing an upper constraint on the total galactic mass that could produce their observed velocities. Please also see: Bratek et al, (2011), "Keplerian Ensemble Approximation. The issue of motions of Galactic halo compact objects", http://arxiv.org/abs/1108.1629
These new findings, along with the questionable presumption used to infer the existence of galactic dark matter - that individual disk objects independently orbit some single dominating mass, should be enough to justify a rigorous reevaluation of galactic gravitation and redetermine whether any 'missing' mass might be required to produce observed galactic rotational characteristics.
posted by James Dwyer
February 11, 2012
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