Current View of Dark Matter

Current View of Dark Matter:
The current observations and estimates of dark matter is that 1/2 of dark matter is probably in the
form of massive neutrinos, even though that mass is uncertain. The other 1/2 is in the form of
stellar remnants and low mass, brown dwarfs. However, the combination of both these mixtures
only makes 10 to 20% the amount mass necessary to close the Universe. Thus, the Universe
appears to be open.

Origin of Structure :
As we move forward in time from the beginning of the Universe we pass through the
inflation era, baryongenesis, nucleosynthesis and radiation decoupling. The culmination is
the formation of the structure of matter, the distribution of galaxies in the Universe.
During radiation era growth of structure is suppressed by the tight interaction of photons
and matter. Matter was not free to response to its own gravitational force, so density
enhancements from the earliest times could not grow.
Density enhancements at the time of recombination (having their origin in quantum
fluctuations that expanded to galaxy-sized objects during the inflation era) have two
routes to go. They can grow or disperse.

The `pressure effects' that density enhancements experience are due to the expanding
Universe. The space itself between particles is expanding. So each particle is moving
away from each other. Only if there is enough matter for the force of gravity to overcome
the expansion do density enhancements collapse and grow.