Re: "Scientists named it dark matter as it did not seem to emit any light"
@iglethal: I agree... the problem may be largely one of experimental capability
The most recently released 'switch on' of the SKA 16 element segment in South Africa increased the known galaxies in a moon sized area of the sky from 19 to somewhere near 1200 in the few minutes it took to collect some radiation. It looks like the brown dwarf content of galaxies also looks set for some serious revision... perhaps also 2-order of magnitude like at 'proto-SKA' . SKA will have 4 types the resolving power when complete at 64 elements. But then it will link with the Australian and South American patches in a substantially more sensitive composite array. Can we reasonably outlook a 10-magnitude increase in galactic count estimates... when looking out of the Milky Way!!?
How many orders of magnitude of underestimation do we need for us to fully account for 'dark' matter?
If galactic bending of light is greater than expected from current mass estimates we also need to consider where those estimates of galactic mass come from. Are we extrapolating errors that we make due to brown dwarf underestimation in our 'reference' galaxies?
Just an observational issue... from a lay perspective. If you put a bunch of garbage in a wind centrifuge the heaviest items fall near the centre and the lighter stuff accelerates out to the periphery. If you have more light stuff than heavy stuff then the most mass ends up 'out there'. Just look at where and how gas giants form sweeping up the light far flung elements in solar systems.
So why do the great and revered amongst us not apply the same expectation to the construction galaxies and integrate that with the expansion from the big bang? Putting Big Bang trajectory components aside for the moment. We can expect a great deal of unlit and widely scattered small light, and un-lit, objects at the edge of galaxies where they will tend to contribute to faster angular momentum.
These objects will have built up from ejecta of star deaths, and at an earlier stages perhaps from the big bang condensations, and will have transferred some of the energy of their original acceleration along their original path into 'orbital' energy, as their path is bent towards an arc under the gravitational influence of the heavy matter at and nearer to any galactic object they approach, They will acquire the galactic spin direction if they are captured or may be sling-shot off to some other destination until they get captured. So we have a picture of galaxies 'hoovering up' light objects which tend to attach to their periphery and of heavy objects with greater momentum penetrating closer to their centres and accumulating there before gaining a measure of 'orbital' stability. Since small stuff, starting at the elemental levels, in the universe seems to outweigh big stuff we can expect more mass at lower densities to be captured in the periphery of galaxies than at their centres... since all galactic mass is acquired in the same way (just like planetary masses). They do not create their own mass nor is it all 'given' by their aggregation of locally present material in a wrinkle of expanding space time determined by the matter distribution at the time of its condensation. The pot has been stirred many times since then while it continues to boil vigorously!
Is that a suitable practical basis for building an explanatory model of why the outer edges of galaxies seem to spin faster than we would expect them to when considering the theory together with the very incomplete measurements we have acquired in, what is after all only, the last couple of decades?
Rob E Jarvis