Dark Matter

Definition

Dark matter is an unseen form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. It plays a crucial role in the structure and evolution of the universe, influencing galaxy formation, cosmic expansion, and the distribution of galaxies within the cosmic web.

5 Must Know Facts For Your Next Test

1. Approximately 27% of the universe's total mass-energy content is made up of dark matter, while visible matter accounts for only about 5%.
2. The evidence for dark matter primarily comes from its gravitational effects on galaxies and galaxy clusters, such as the rotation curves of spiral galaxies showing more mass than what is visible.
3. Dark matter is hypothesized to exist in various forms, including weakly interacting massive particles (WIMPs) and axions, which are candidates for dark matter particles.
4. The cosmic web, which consists of filaments and voids, is influenced significantly by dark matter, helping to shape the large-scale structure of the universe.
5. Dark matter's existence has profound implications for cosmological models, affecting our understanding of galaxy formation, evolution, and the overall dynamics of the universe.

Review Questions

• How does dark matter influence the formation and distribution of galaxies within the cosmic web?
  • Dark matter acts as a scaffolding for galaxy formation by providing the necessary gravitational pull for gas and baryonic matter to coalesce into galaxies. As galaxies form within regions dense with dark matter, their distribution follows a web-like structure known as the cosmic web. This dark matter framework not only shapes where galaxies are located but also affects their dynamics and interactions with one another over cosmic time.
• Discuss how gravitational lensing provides evidence for the existence of dark matter in galactic clusters.
  • Gravitational lensing occurs when a massive object, like a galactic cluster filled with dark matter, bends light from objects behind it. By analyzing how much light is bent and where it appears distorted, astronomers can infer the amount and distribution of mass in the foreground cluster. Since dark matter does not emit light and can only be detected through its gravitational influence, gravitational lensing serves as one of the primary methods for demonstrating its presence in large structures.
• Evaluate the significance of dark matter in our understanding of cosmological parameters and models concerning the fate of the universe.
  • Dark matter is crucial for cosmological models because it contributes significantly to the overall mass-energy budget of the universe. Its presence affects key parameters such as density, expansion rate, and gravitational interactions among cosmic structures. Understanding dark matter helps refine predictions about future scenarios for the universe's fate, such as whether it will continue expanding indefinitely or eventually collapse. Thus, acknowledging dark matter reshapes our perspectives on cosmology and offers insights into fundamental questions about the universe's ultimate destiny.

Related terms

Baryonic Matter:

The type of matter composed of protons, neutrons, and electrons that makes up stars, planets, and living organisms; it is the visible matter in the universe.

Gravitational Lensing:

The bending of light from distant objects due to the gravitational influence of massive foreground objects, which can help identify the presence of dark matter.

Cosmic Microwave Background (CMB): The remnant radiation from the Big Bang that provides evidence for the existence of dark matter through its effects on large-scale structure formation.