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Does invisible matter exist?
Two arguments support the idea that some invisible substance exists in the Universe. The first is dynamic. It starts from observation of motions under the effect of gravity. The second is related to Big Bang nucleosynthesis, i.e. nuclear cosmology, which combines cosmology and nuclear physics.
Dynamical proof
The first observation is that, if we can go by what light is telling us, most of the matter in the Galaxy (and indeed any galaxy) is concentrated in the galactic bulge, a marked, reddened swelling at the centre of the star distribution. Therefore, if we assume that the mass distribution of luminous objects is representative of the total mass distribution in galaxies, every spiral galaxy should behave like a vast Solar System, with the stars and clouds playing the role of planets and the galactic bulge that of the Sun.
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