We observe the universe around us through many scientific means. However it is through the electromagnetic spectrum, that is everything from radio waves to gamma waves, that we learn about the objects in our world and beyond. However we can also learn about our universe through indirect means, such as the effect of gravity on light as well as larger objects like our galaxy. In fact it is this indirect method of observation that has led us to the discovery of extra-solar planets. As it turns out this indirect method has brought about the discovery of a new and strange material that may well constitute ninety percent of our universe. Where once we believed space was nothing more than random stars and planets and gas floating endlessly in a sea of nothingness, we now have proof that our galaxy and countless others are floating on and ocean of a yet unknown substance named dark matter.
Of all the mysteries in our universe none is more difficult to understand as dark matter. Astronomers know its there due to the unusual bending of light in places where nothing but empty space exists as well as the unusual movement of stars and galaxies that can not be accounted for. The dark matter problem arose because of a mismatch in the masses of galaxies and larger cosmic structures. The constituents of these systems-stars and gas in the case of galaxies, gas and galaxies in the case of galaxy clusters-move about but do not escape, because they are checked by the gravitational pull from the rest of the system. The laws of physics tell us how much mass has to be present to counterbalance the motions and thereby prevent the dispersal of the system. Disconcertingly, the tally of mass that astronomers actually observe falls far short of that. (Quote1) Dark matter is the only explanation that scientists can come up with for these un-matching totals.