CMB analysis has been used by astronomers to map the distributions of dark matter throughout the galaxy. Dark matter is not subject to electromagnetic interaction. It does not emit waves.
Scientists observed the galaxy to fix it. It is located behind the gravitational lenses (a huge body that changes electromagnetic radiation’s direction with its gravitational fields, much like an ordinary lens changes a light beam’s direction) and outside it. This can be used for determining how much light has been distorted. The galaxy’s mass and dark matter will be greater if there is more distortion.
Scientists examined over 1.5 million lens galaxies at a distance of approximately 12 billion light-years from Earth to collect the data. Scientists also used data from the Planck satellite to observe the cosmic microwave background, which is the thermal radiation that evenly fills our universe.
They found dark matter 12 million years old by combining a sample from a distant galaxy with lens distortion in CMB. It is 1.7 billion years younger that the Universe.