Cold dark matter

Definition

Cold dark matter (CDM) is a hypothetical form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. This type of dark matter is believed to clump together slowly, forming structures such as halos around galaxies, and plays a critical role in the formation and evolution of cosmic structures. It influences the behavior of galaxies and galaxy clusters, providing a framework for understanding the large-scale structure of the universe.

5 Must Know Facts For Your Next Test

1. Cold dark matter contributes to about 27% of the total energy density of the universe, with normal matter making up only about 5%.
2. The CDM model helps explain the observed distribution of galaxies and clusters in the universe, accounting for the 'missing mass' that cannot be explained by visible matter alone.
3. CDM is thought to form structures early in the universe's history, providing a scaffold for galaxies to form and grow over time.
4. Observations of cosmic microwave background radiation provide evidence supporting the existence of cold dark matter by showing fluctuations consistent with its predicted distribution.
5. Computer simulations of cosmic evolution show that cold dark matter leads to a hierarchical structure formation scenario, where smaller structures merge to form larger ones.

Review Questions

• How does cold dark matter contribute to the formation of galaxy halos?
  • Cold dark matter plays a vital role in forming galaxy halos by clumping together under gravity over time. This clustering creates regions where normal matter can coalesce, leading to star formation and the development of galaxies. As CDM accumulates in these halos, it provides the gravitational framework necessary for galaxies to maintain their structure and evolve.
• Discuss how gravitational lensing provides evidence for cold dark matter in galaxy clusters.
  • Gravitational lensing occurs when massive objects like galaxy clusters warp spacetime, causing light from more distant objects to bend around them. This effect allows astronomers to map the distribution of mass in these clusters, revealing more mass than what is visible through stars and gas alone. The discrepancy between visible mass and gravitational effects strongly suggests the presence of cold dark matter in significant amounts.
• Evaluate the significance of WIMPs as candidates for cold dark matter and their implications for our understanding of the universe.
  • Weakly Interacting Massive Particles (WIMPs) are a leading candidate for cold dark matter due to their theoretical properties that align with observed cosmic phenomena. Their existence would explain why dark matter interacts so weakly with normal matter, accounting for the large amount of unseen mass inferred from gravitational effects. Discovering WIMPs would not only validate the cold dark matter model but also provide insights into particle physics beyond the Standard Model, potentially reshaping our understanding of the fundamental components of the universe.

Related terms

Galaxy Halo: A galaxy halo is a roughly spherical region surrounding a galaxy, containing dark matter, hot gas, and stars that are gravitationally bound to the galaxy.

Gravitational Lensing: Gravitational lensing is the bending of light from distant objects due to the gravitational influence of massive objects, such as galaxy clusters, which can indicate the presence of dark matter.

WIMPs: Weakly Interacting Massive Particles (WIMPs) are a leading candidate for cold dark matter; they are theoretical particles that interact via weak nuclear force and gravity.