"The Dark Side of the Universe: Beyond Stars and the Star Stuff We are Made of"
The sky is filled with hundreds of billion galaxies, all
lit up by their stars.
Stars account for less than one percent of the material
in the Universe, and g
alaxies are held together by a new form of matter --
dark matter -- that
accounts for 1/3 of the stuff in the Universe.
The other 2/3 exists as in an
even more mysterious form -- dark energy -- and is causing
the expansion of
the Universe to speed up, rather than slow down.