Recent observations may have detected an enormous filament of dark matter, along which a group of 14 galaxies are developing.
Dark Matter represents about 22 percent of the total mass of observable universe, yet does not interact with "normal" luminous matter and cannot be seen by human eyes. Dark Energy and Dark matter represent up to 75 percent of the energy-matter in the observable universe. While not seen, both can be inferred by their effect on surrounding matter.
We just don't know exactly what they are.
In a beautiful 2006 image from the Chandra X-Ray Observatory, above, the blue color is believed to represent the invisible Dark Matter of colliding galaxies. Because is does not interact with the normal luminous matter (pink), it passed through the merging galaxies ahead of the observable matter and is headed in opposite directions in the image. Astronomers detected it by observing how much gravity bends the light from the stars behind the blue area, a technique known as gravitational lensing. More massive objects bend more light.