Dark matter is a mysterious and invisible form of matter that makes up approximately 27% of the total mass-energy content of the universe. Unlike ordinary matter, dark matter does not emit, absorb, or reflect light, making it completely invisible to telescopes that detect electromagnetic radiation.
Why Do Scientists Believe It Exists?
Dark matter cannot be seen directly, but its gravitational effects are observable:
- Galaxy Rotation Curves: Stars in galaxies rotate at speeds that can’t be explained by the visible matter alone. The outer regions of galaxies rotate just as fast as the inner regions, suggesting there’s additional unseen mass holding them together.
- Gravitational Lensing: Light from distant galaxies is bent more than expected when passing near massive objects, indicating the presence of extra, invisible mass.
- Large-Scale Structure Formation: Computer simulations show that the clumping of galaxies and galaxy clusters in the universe can only be explained if dark matter was present during the early stages of cosmic evolution.
- Cosmic Microwave Background: Variations in the CMB support models that include dark matter to match the observed structure and composition of the universe.
What Is Dark Matter Made Of?
The exact composition of dark matter remains unknown. It is not made of atoms, and it doesn’t interact via the electromagnetic force. The leading candidates are WIMPs (Weakly Interacting Massive Particles) and axions, although none have been detected directly yet.
Understanding dark matter is one of the greatest challenges in modern astrophysics and particle physics, as it holds crucial clues to the nature and fate of the universe.