Dark Matter – Definition & Detailed Explanation – Cosmology Glossary

I. What is Dark Matter?

Dark matter is a mysterious substance that makes up about 27% of the universe. It does not emit, absorb, or reflect light, making it invisible and undetectable through traditional means. Despite its elusive nature, scientists have been able to infer its existence through its gravitational effects on visible matter, such as galaxies and galaxy clusters.

II. How is Dark Matter Detected?

Dark matter cannot be directly observed, but its presence can be inferred through its gravitational effects on visible matter. One common method of detecting dark matter is through the observation of the rotation curves of galaxies. These curves show that the velocity of stars in galaxies does not decrease as expected with distance from the center, indicating the presence of unseen mass.

Another method of detecting dark matter is through gravitational lensing, which occurs when the gravitational field of dark matter bends and distorts light from distant objects. By studying the bending of light, scientists can map the distribution of dark matter in the universe.

III. What is the Composition of Dark Matter?

The composition of dark matter is still unknown, as it does not interact with electromagnetic radiation. However, scientists have proposed several candidates for dark matter particles, including weakly interacting massive particles (WIMPs), axions, and sterile neutrinos.

WIMPs are a leading candidate for dark matter and are predicted to interact weakly with regular matter. Axions are hypothetical particles that are extremely light and have low interaction rates with other particles. Sterile neutrinos are neutrinos that do not interact through the weak nuclear force, making them difficult to detect.

IV. What is the Role of Dark Matter in the Universe?

Dark matter plays a crucial role in the formation and evolution of the universe. It provides the gravitational pull necessary to hold galaxies and galaxy clusters together, preventing them from flying apart due to their high speeds. Without dark matter, galaxies would not have formed as they did, and the universe would look vastly different.

Additionally, dark matter is believed to have played a key role in the formation of large-scale structures in the universe, such as galaxy clusters and superclusters. Its gravitational influence helped to shape the distribution of matter in the early universe, leading to the structures we see today.

V. What are Some Theories about the Nature of Dark Matter?

There are several theories about the nature of dark matter, ranging from exotic particles to modifications of gravity. One popular theory is the supersymmetry theory, which predicts the existence of new particles that could account for dark matter. However, experiments at the Large Hadron Collider have not yet found evidence of these particles.

Another theory is the axion theory, which proposes the existence of extremely light particles that could explain dark matter. Axions are currently being searched for in laboratory experiments, but their existence has not yet been confirmed.

Some scientists have also proposed modifications to the laws of gravity, such as the MOND (Modified Newtonian Dynamics) theory, as an alternative explanation for the observed effects of dark matter. However, these theories have not gained widespread acceptance in the scientific community.

VI. How Does Dark Matter Interact with Regular Matter?

Dark matter interacts with regular matter primarily through gravity, as it exerts a gravitational pull on visible matter. However, dark matter particles are believed to interact weakly with regular matter through the weak nuclear force, making them difficult to detect.

Despite its weak interactions, dark matter has a significant impact on the universe. Its gravitational effects shape the distribution of matter on large scales, influencing the formation of galaxies and galaxy clusters. Understanding the interactions between dark matter and regular matter is crucial for unraveling the mysteries of the universe and the nature of dark matter itself.