As a result of my research into the subject of dark matter I noticed that the story of dark matter really must be understood in two parts. First, I looked into the reasons that we know dark matter even exists. Second, I had to examine possible explanations as to what it is. Therefore I thought I would start my explanation where the story begins, discovery. Realizing there is dark energy working in the Universe created a whole new field of study, understanding how that new energy affected expansion meant astronomers had to prove that dark matter and dark energy exists at all. So, what is really fueling and filling the Universe?
In 1998 the Hubble Space Telescope (HST) observed a very distant supernovae, this observation indicated that, a long time ago, the Universe was actually expanding even slower than it is today. The accepted theory before this was that the expansion of the Universe had been slowing due to gravity, when in fact it has been accelerating.
No one expected this; no one knew how to explain it. But something was causing it. Hypotheses developed such as the existence of some strange kind of energy-fluid that filled space. People even speculated that there was something wrong with Einstein's theory of gravity and a new theory was necessary that include some kind of field that creates this cosmic acceleration. Theorists actually still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.
Scientists have learned how much dark energy there is because they know how it affects the Universe's expansion but other than that, it is still a complete mystery. I learned from the NASA Science web site:
"Roughly 68% of the Universe is dark energy. Dark matter makes up about...