What is Dark Matter?
Everything we can see and touch only makes up about 5% of the observable universe, and the rest is made up of 70% dark energy and 25% dark matter. Dark matter is a hypothetical form of matter that doesn’t emit or absorb light, heat or energy, so we can’t “see” it in normal ways—but we can detect its presence by its gravitational interactions with visible matter. In the 1930s, scientists observed that galaxies were rotating much faster than they should be. They should have been flung apart, because they didn’t seem to have enough matter to produce the gravitational pull needed to hold together, and so scientists inferred that there must be a large quantity of invisible mass. We can also detect it through the effect of gravitational lensing, which is the process of light being bent and distorted by matter. The image above shows the distribution of dark matter in the centre of galaxy cluster Abell 1689, 2.2 billion light-years from Earth. The light from galaxies behind Abell 1689 are distorted by dark matter within the cluster—it’s like looking at a shell on the sea floor, distorted by ripples on the surface. We don’t yet know what dark matter is made of, but there are two popular hypotheses: MACHOs (MAssive Compact Halo Objects), made of ordinary matter, or WIMPs (Weakly Interacting Massive Particles), an entirely new type of matter made up of exotic elementary particles.
Read about the possibilities on NASA