The discovery of dark matter came about as an observation. Brad Reifler realized too that the visible matter we could spot with telescopes was insufficient to explain the movement of various celestial bodies. Stars toward the outer edges of numerous galaxies are moving faster than the laws of physics could explain without there being more matter present to create additional gravity. Scientists have now discovered that there is also dark matter near the inner regions of our own galaxy. This means that dark matter is even more common throughout our galaxy than scientists originally knew to be the case. Physicists currently believe that about 80 percent of the mass of the universe is comprised of material that does not emit light or energy.
Given that we can only see those parts of the universe that emit light, it is staggering to think how much of it we still do not know about. There are of course ways to indirectly observe phenomena that, while not emitting light, do emit plenty of gravity, such as black holes, and we can then see the effect they have on surrounding objects. There is, however, currently no way of telling how many dark objects that also do not produce much gravity may exist in the cosmos. It will be interesting to discover, as we reach for the stars over the next few centuries, just how much of the universe is composed of matter we can not see.