Sunday, December 23, 2007

Two stellar components in the halo of Milky Way

Bohr orbit model for astrophysical objects suggests that also galactic halo should have a modular structure analogous to that of planetary system or the rings of Saturn rather than that predicted by continuous mass distribution. Quite recently it was reported that the halo of Milky Way - earlier thought to consist of single component - seems to consist of two components (see the article of Carolle et al in Nature. See also this and this).

Even more intriguingly, the stars in these halos rotate in opposite directions. The average velocities of rotation are about 25 km/s and 50 km/s for inner and outer halos respectively. The inner halo corresponds to a range 10-15 kpc of orbital radii and outer halo to 15-20 kpc. Already the constancy of rotational velocity is strange and its increase even stranger. The orbits in inner halo are more eccentric with axial ratio rmin/rmax≈ .6. For outer halo the ratio varies in the range .9-1.0. The abundances of elements heavier than Lithium are about 3 times higher in the inner halo which suggests that it has been formed earlier.

Bohr orbit model would explain halos as being due to the concentration of visible matter around ring like structures of dark matter in macroscopic quantum state with gigantic gravitational Planck constant. This would explain also the opposite directions of rotation.

One can consider two alternative models predicting constant rotation velocity for circular orbits. The first model allows circular orbits with arbitrary plane of rotation, second model and the hybrid of these models only for the orbits in galactic plane.

  1. The original model assumes that galactic matter has resulted in the decay of cosmic string like object so that the mass inside sphere of radius R is M(R) propto R.
  2. In the second model the gravitational acceleration is due to gravitational field of a cosmic string like object transversal to the galactic plane. String creates no force parallel to string but 1/ρ radial acceleration orthogonal to the string. Of course, there is the gravitational force created by galactic matter itself. One can also associate cosmic string like objects with the circular halos themselves and it seems that this is needed in order to explain the latest findings.

The big difference in the average rotation velocities < vφ>; for inner and outer halos cannot be understood solely in terms of the high eccentricity of the orbits in the inner halo tending to reduce < vφ>. Using the conservation laws of angular momentum (L= mvminρmax) and of energy in Newtonian approximation one has < vφ>= ρmaxvmin< 1/ρ>. This gives the bounds

vmin< < vφ>< vmax= vminmaxmin]≈ 1.7 vmin .

For both models v=v0= k1/2, k=TG, (T is the effective string tension) for circular orbits. Internal consistency would require vmin<< vφ>≈.5v0<vmax≈ 1.7 vmin. On the other hand, vmax<v0 and thus vmin>.6v0 must hold true since the sign of the radial acceleration for ρmin is positive. Obviously 0.5v0>v>sub>min>.6v0 means a contradiction.

The big increase of the average rotation velocity suggests that inner and outer halos correspond to closed cosmic string like objects around which the visible matter has condensed. The inner string like object would create an additional gravitational field experienced by the stars of the outer halo. The increase of the effective string tension by factor x corresponds to the increase of < vφ> by a factor x1/2. The increase by a factor 2 plus higher eccentricity could explain the ratio of average velocities.

For details see the new chapter Quantum Astrophysics of "Classical Physics in Many-Sheeted Space-Time.


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