Cold dark matter

Definition

Cold dark matter (CDM) is a theoretical form of matter that does not emit or interact with electromagnetic radiation, making it invisible to direct observation. CDM is thought to play a crucial role in the formation and evolution of structures in the universe, influencing everything from the distribution of galaxies to the behavior of cosmic structures over time. Its properties help scientists understand how quantum fluctuations in the early universe can lead to the large-scale structure we observe today.

5 Must Know Facts For Your Next Test

1. Cold dark matter is believed to make up about 27% of the total mass-energy content of the universe, with ordinary matter comprising only about 5%.
2. Unlike hot dark matter, cold dark matter moves slowly compared to the speed of light, allowing it to clump together and form gravitational wells that attract baryonic matter.
3. The presence of cold dark matter is inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe.
4. Models including cold dark matter help explain the observed cosmic microwave background radiation patterns and galaxy formation.
5. Cold dark matter candidates include weakly interacting massive particles (WIMPs) and axions, both of which are yet to be directly detected.

Review Questions

• How do quantum fluctuations relate to the formation of large-scale structures in a universe dominated by cold dark matter?
  • Quantum fluctuations in the early universe created tiny density variations that served as the seeds for structure formation. In a universe dominated by cold dark matter, these fluctuations could grow over time due to gravitational attraction, leading to regions of higher density where galaxies and clusters would eventually form. Cold dark matter’s ability to clump together allowed it to exert significant gravitational influence, enabling baryonic matter to fall into these potential wells and contribute to structure formation.
• What distinguishes cold dark matter from other types of dark matter in terms of its properties and implications for cosmological models?
  • Cold dark matter differs from hot dark matter primarily in its velocity; cold dark matter particles move slowly compared to light. This slow movement allows for clumping, which is essential for forming structures like galaxies. In contrast, hot dark matter tends to remain diffuse due to its high speeds and does not clump effectively. This distinction is crucial for cosmological models, such as the ΛCDM model, as they rely on cold dark matter's properties to accurately describe the observed universe's structure and evolution.
• Evaluate the implications of cold dark matter on our understanding of galaxy formation and cosmic evolution within the context of current cosmological theories.
  • The presence of cold dark matter significantly impacts our understanding of galaxy formation and cosmic evolution. By providing a framework for how gravitational forces shape structures over time, cold dark matter helps explain why galaxies are distributed as they are and how they interact. Current cosmological theories that incorporate cold dark matter can accurately predict phenomena like galaxy clustering and the cosmic microwave background radiation patterns. These insights enhance our knowledge about the universe's history and offer directions for future research into both dark matter candidates and potential detection methods.

Related terms

Baryonic Matter:

Baryonic matter is the type of matter composed of protons, neutrons, and electrons, which makes up stars, planets, and living beings.

Structure Formation:

Structure formation refers to the process by which small density fluctuations in the early universe grow over time to form galaxies, clusters, and larger cosmic structures.

ΛCDM Model: The ΛCDM model is the standard model of cosmology that describes the evolution of the universe, incorporating both cold dark matter and dark energy as key components.