Dark Matter

Definition

Dark matter is a mysterious and invisible form of matter that does not emit, absorb, or reflect light, making it undetectable by traditional astronomical methods. Despite being unseen, it makes up about 27% of the universe's total mass-energy content and plays a crucial role in the structure and evolution of galaxies, influencing gravitational interactions in the cosmos.

5 Must Know Facts For Your Next Test

1. Dark matter does not interact with electromagnetic forces, which is why it cannot be seen directly with telescopes or other instruments that rely on light.
2. The presence of dark matter is inferred from its gravitational effects on visible matter, such as the rotation curves of galaxies that show they rotate faster than expected based on their visible mass.
3. It is believed that dark matter contributes to the large-scale structure of the universe, acting as a scaffold around which galaxies and galaxy clusters form.
4. Various experiments are being conducted to detect dark matter particles directly or indirectly, including those at underground laboratories and particle colliders.
5. The nature of dark matter remains one of the biggest unsolved mysteries in astrophysics, with several candidates proposed, such as WIMPs (Weakly Interacting Massive Particles) and axions.

Review Questions

• How does dark matter influence the motion of galaxies and their rotation curves?
  • Dark matter significantly influences the motion of galaxies by exerting gravitational forces that are not accounted for by visible matter alone. Observations show that galaxies rotate at speeds that would not keep them intact based solely on the mass we can see. The extra gravitational pull from dark matter, which makes up most of a galaxy's mass, explains why stars at the outer edges of galaxies move at similar speeds to those near the center. This discrepancy is crucial for understanding galaxy dynamics and formation.
• In what ways do observations of cosmic microwave background radiation provide insights into the existence and distribution of dark matter in the universe?
  • Observations of cosmic microwave background radiation give important clues about dark matter through measurements of temperature fluctuations across the sky. These fluctuations indicate how matter was distributed in the early universe and how it evolved over time. Dark matter's gravitational effects helped shape this distribution, influencing where baryonic matter clustered to form galaxies. By analyzing these patterns, scientists can infer the density and properties of dark matter throughout cosmic history.
• Evaluate how understanding dark matter contributes to our overall knowledge of cosmic evolution and structure formation in the universe.
  • Understanding dark matter is essential for comprehending cosmic evolution and structure formation because it constitutes a large portion of the universe's mass-energy content. The influence of dark matter on gravity affects how galaxies form, collide, and evolve over billions of years. If we can determine its nature and properties, it could refine models of cosmic evolution, explaining phenomena like galaxy clustering and cosmic web structure. Ultimately, unraveling the mysteries surrounding dark matter could revolutionize our understanding of the fundamental forces shaping our universe.

Related terms

Baryonic Matter: Baryonic matter is the ordinary matter made up of protons, neutrons, and electrons that forms stars, planets, and living organisms.

Gravitational Lensing: Gravitational lensing occurs when the gravity of a massive object, like a galaxy or cluster of galaxies, bends the path of light from objects behind it, providing indirect evidence of dark matter.

Cosmic Microwave Background Radiation: Cosmic microwave background radiation is the remnant radiation from the Big Bang that fills the universe and provides evidence for the early state of the cosmos, including insights into dark matter's influence on structure formation.