It is hard to imagine that when we look around on our planet, at ourselves, and up at the day and night sky, that everything we see is avery small percentage of the total mass of the Universe. Most of the Universe is comprised of Dark Energy which is forcing the Universe to expand at an ever increasing rate and Dark Matter - matter that we know is there but cannot see. Only 4 percent of the Universe is made up of ordinary matter - the atoms that comprise stars, planets and us!
We know Dark Matter exists because of the gravitational affect it has on that 4% of ordinary matter. The stars in our Milky Way Galaxy orbit faster than they should when taking into account all of the visible matter. Other galaxies do the same all as a result of some unseen matter.
Astronomers have estimated that 23% of the Universe is comprised of Dark Matter and 73% is Dark Energy with our ordinary atoms/matter filling in the remaining 4%. Astronomers have recently been able to map the distribution of Dark Matter on the largest scale to dat and the resulting picture is very telling:
This incredible picture is the result of five years' work observing 10 million galaxies in four sections of the sky and computer analysis. The light from the galaxies located at a distance of six billion light years, was bent by Dark Matter that lie between us and the galaxies. The Universe was half its current age when the light from these galaxies was emitted.
Plans are already underway to expand the survey to cover an area 10 times larger and thereby provide an even greater understanding of the distribution of Dark Matter.
Read More About It: http://www.cfhtlens.org/ and http://www.cfht.hawaii.edu/en/news/CFHTLens/.
Sky Guy in VA