The Bullet cluster has been a poster child for the dark side for years. The cluster is shown below (Source: NASA/CXC/M.Weiss - Chandra X-Ray Observatory). The pink areas show the lit matter that can be seen through a telescope, ie: that actually exists. The idea is that the pink 'bullet' on the right has smashed through the pink 'target' on the left and is still moving rightwards.
Using the stars behind the cluster and distortions in them, it is possible to find out the amount of light bending (lensing) going on in the field of view and therefore, they assume, the invisible mass that is there. This is shown by the blue areas. This is their dark matter. For years they have been saying that the Bullet cluster proves the existence of dark matter because the dark is obviously separated from the visible.
However, it was very clear to me that this system is spinning. The bullet at least is spinning, as real bullets do, around the axis which is horizontal, and the blue areas look as if they are along that spin axis. This is a clear prediction of quantised inertia, see my flyby anomaly paper (ref 1) in which space probes speed up near to the Earth's spin axis. This is a schematic of the cluster:
I'd been mulling this over for years, but last year I asked a student to find some data on these clusters (masses and radii) and then I calculated where the acceleration would be as low as 2x10^-10 m/s^2, calculating on a grid and adding both the gravitational accelerations (GM/r^2) and mutual rotational acceleration (v^2/r). This QI-zone is present of course in all regions away from the cluster but is especially large in just the areas shown by blue in the famous diagram (see the blue in both diagrams above). The hypothesis is that along the spin axis mutual acceleration are very low and QI bends light there, mimicking the effect of matter.
They used to ask "Can MoND take a Bullet?" Well, MoND can't, but QI seems to do fine.
References
McCulloch, M.E., 2008. Modelling the flyby anomalies using a modification of inertia. MNRAS Letters, 389 (1), L57-60
