Dark energy makes up most of the universe, but dark matter also covers a sizeable chunk. Comprising nearly 27 percent of the universe, and 80 percent of the matter, dark matter also plays a dominant role.
Like dark energy, dark matter continues to confound scientists. While dark energy is a force that accounts for the expanding universe, dark matter explains how groups of objects function together.
In the 1950s, scientists studying other galaxies expected gravity to cause the centers to rotate faster than the outer edges, based on the distribution of the objects inside of them. To their surprise, both regions rotated at the same rate, indicating that the spiral galaxies contained significantly more mass than they appeared to. Studies of gas inside elliptical galaxies and of clusters of galaxies revealed that this hidden matter was spread throughout the universe.
Scientists have a number of potential candidates for dark matter, ranging to incredibly dim objects to strange particles. But whatever the source of both dark matter and dark energy, it is clear that the universe is affected by things that scientists can't conventionally observe.