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Jun10-05, 05:49 PM
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Quote Quote by SpaceTiger
They're not weakly interacting gravitationally. In that respect, they act the same as any other form of mass/energy. A spherical "halo" is a natural configuration for a collection of bodies interacting only by the gravitational force.
Are you saying that the dark matter halos are naturally spherical, and that the spherical distribution can account for the galactic rotation curves of all galaxies? My understanding is that the DM spheres must have hollow cores with specific density gradients to explain flat galactic rotation curves.

Here's a quick example, using lensing to estimate galactic mass distributions.

The cold dark matter theory predicts that dark matter should clump together in the centre of galaxies and dominate the galactic centre. In the galaxy we studied, however, the dark matter plays an insignificant role in its centre, accounting for less than 4% of the mass within the gravitationally lensed images. Instead the mass here is dominated by the stars in the bulge of the galaxy.

The dark matter does play a very large role in the overall galaxy, contributing about 60% of the total mass within the radius of the visible light of the galaxy, but its contribution is primarily to the outer regions. Other work has suggested a similar distribution of dark matter in other galaxies, but this is the first galaxy to be used that definitively discredits the current theory.
From the same authors: