As I have repeated many times on this blog, galaxies spin far too fast to be bound by their visible matter. This anomaly disagrees with standard physics and yet it has not only been brushed under the carpet, but it has been forbidden in many places to even admit that there is a carpet. A serious flaw (floor) in the mainstream attitude :) The carpet is the dark matter that has been invented to cover this up and save general relativity (which may be fine for high acceleration, but does not work for low).
There are two cases though, in which the dark matter fudge cannot be applied 1) globular clusters (see Scarpa et al., 2008 below) and 2) wide binaries which are even better (discussed earlier here). Wide binaries are twin star systems that orbit with a separation of more than 7000 AU and they show the same impossibly fast orbits that larger galaxies do. Dark matter cannot be used to fudge them because in order for dark matter to predict galaxy rotation it must stay spread out and therefore it cannot be squeezed into little wide binary systems. So wide binaries are the astrophysics equivalent of testing the emdrive in a vacuum which rules out air currents - wide binaries rule out dark matter.
I have started looking a wide binaries again, going back to a paper of Hernandez et al. (2014) who processed a lot of data on them. The data is shown in the Figure by the blue and red crosses. The x axis shows the separation of each pair in parsecs and the y axis is their orbital speed (km/s). I've shown the uncertainty in the data crudely by the blue and red coloured areas around the crosses, so you can see that the SDSS data (blue) is far less accurate then the Hipparcos data (red). To be deemed successful a theory has to predict within the blue and red areas.
There are two cases though, in which the dark matter fudge cannot be applied 1) globular clusters (see Scarpa et al., 2008 below) and 2) wide binaries which are even better (discussed earlier here). Wide binaries are twin star systems that orbit with a separation of more than 7000 AU and they show the same impossibly fast orbits that larger galaxies do. Dark matter cannot be used to fudge them because in order for dark matter to predict galaxy rotation it must stay spread out and therefore it cannot be squeezed into little wide binary systems. So wide binaries are the astrophysics equivalent of testing the emdrive in a vacuum which rules out air currents - wide binaries rule out dark matter.
I have started looking a wide binaries again, going back to a paper of Hernandez et al. (2014) who processed a lot of data on them. The data is shown in the Figure by the blue and red crosses. The x axis shows the separation of each pair in parsecs and the y axis is their orbital speed (km/s). I've shown the uncertainty in the data crudely by the blue and red coloured areas around the crosses, so you can see that the SDSS data (blue) is far less accurate then the Hipparcos data (red). To be deemed successful a theory has to predict within the blue and red areas.
I have added to the plot the predictions of general relativity (the dotted curve) which lies outside the coloured areas for all separations greater than about 0.03 parsecs. Therefore, because dark matter cannot be applied in these cases (unless they add more bells and whistles to it) we can say that general relativity has been falsified. This is a strong indication that it is wrong in galaxies as well, since the anomalies are very similar.
The other curves show Modified Newtonian dynamics (MoND, the dashed curve) and quantised inertia (the solid curve). Both theories predict the data, but MoND has been tuned to work by arbitrary adjustment of its free parameter. Quantised inertia predicts the data all by itself, without any tuning, an advantage which shows it is deeper, more predictive (it can predict the change in the systems' rotation with cosmic time too) and also simpler. Occam's razor cannot be repealed. Note that the acceleration used for QI here includes that due to their mutual spin and their movement around the galaxy.
The next steps are to submit this to MNRAS, and try to shrink the blue and red areas of uncertainty in the data using the new GAIA dataset. This is an elegant way to debunk general relativity at these low accelerations, dark matter too, and demonstrate the advantages of QI - better data is needed though.
References
GAIA dataset: http://cdn.gea.esac.esa.int/Gaia/ (Thanks to F.Zagami for the link).
Hernandez X., A. Jimenez, C. Allen,2014. Gravitational anomalies signaling the breakdown of classical gravity. Astrophysics and Space Science Proceedings 38, 43. https://arxiv.org/abs/1401.7063
McCulloch, M.E., 2012. Testing quantised inertia on galactic scales. Astrophys. Space Sci., 342, 575-578. http://arxiv.org/abs/1207.7007
McCulloch, M.E., 2017. Galaxy rotations from quantised inertia and visible matter only. Astrophys. & Space Sci. 362, 149. Link to open access paper
Scarpa et al, 2006. Globular clusters as a test for gravity in the weak acceleration regime. Proceedings of the 1st crisis in cosmology conference. http://arxiv.org/abs/astro-ph/0601581