Dark matter is a hypothetical form of matter that does not interact with light, making it invisible to telescopes. However, its presence is inferred through its gravitational effects on visible matter. Here are some key proofs of dark matter:
1. Galactic Rotation Curves
Galaxies rotate faster than expected based on the visible matter they contain. This discrepancy suggests the presence of an invisible mass that contributes to the gravitational pull. Astronomers observe this "flat rotation curve" in spiral galaxies, where stars and gas at the outer edges move at almost the same speed as those closer to the center.
2. Gravitational Lensing
Light bends around massive objects due to gravity, a phenomenon called gravitational lensing. Astronomers observe strong lensing around galaxies and galaxy clusters, where the light from distant objects is distorted and magnified. The extent of this distortion suggests a larger mass than what is visible, pointing to the presence of dark matter.
3. Cosmic Microwave Background Radiation
The Cosmic Microwave Background (CMB) radiation is a faint afterglow of the Big Bang. The fluctuations in the CMB, which were mapped by the WMAP and Planck satellites, provide evidence for the existence of dark matter. The observed fluctuations in the CMB are consistent with a universe composed of about 85% dark matter and 15% normal matter.
4. Structure Formation in the Universe
The large-scale structure of the universe, such as the distribution of galaxies and galaxy clusters, cannot be explained by the visible matter alone. Simulations show that the formation of these structures requires the presence of dark matter to provide the necessary gravitational pull.
5. Bullet Cluster
The Bullet Cluster is a remarkable example of a collision between two galaxy clusters. In this collision, the hot gas (visible matter) slowed down due to friction, while the dark matter passed through undisturbed. This separation of visible matter and dark matter provides compelling evidence for dark matter.
These observations and theoretical arguments strongly suggest the existence of dark matter, but its exact nature remains a mystery. Scientists are actively searching for direct evidence of dark matter through experiments and observations.
