Dark matter

Definition

Dark matter is an unseen form of matter that does not emit, absorb, or reflect light, making it invisible to current observational instruments. It makes up about 27% of the universe's mass-energy content and plays a crucial role in the formation and structure of galaxies and cosmic structures.

5 Must Know Facts For Your Next Test

1. Dark matter does not interact with electromagnetic forces, meaning it doesn't produce light and is only detectable through its gravitational effects.
2. The rotation curves of galaxies show that stars in the outer regions move much faster than expected based on visible matter alone, indicating the presence of dark matter.
3. Clumps of dark matter are thought to influence the formation of galaxies by acting as gravitational wells that attract baryonic matter.
4. Dark matter helps explain large-scale structures in the universe, such as galaxy clusters and superclusters, which cannot be accounted for by visible matter alone.
5. Current leading candidates for dark matter include weakly interacting massive particles (WIMPs) and axions, although no definitive detection has yet been made.

Review Questions

• How does dark matter influence the rotational dynamics of galaxies?
  • Dark matter significantly affects how galaxies rotate by providing additional gravitational pull that isn't accounted for by visible matter alone. Observations show that stars on the outskirts of galaxies rotate at higher speeds than predicted if only baryonic matter were present. This discrepancy suggests that a substantial amount of unseen mass—dark matter—is distributed throughout and around galaxies, creating a gravitational effect that governs their rotational dynamics.
• Discuss the role of dark matter in the formation and evolution of cosmic structures throughout the universe.
  • Dark matter plays a fundamental role in the formation and evolution of cosmic structures. Its gravitational influence acts as a scaffold for baryonic matter, allowing gas and dust to collapse and form stars and galaxies. Over time, dark matter clumps together, forming large-scale structures like galaxy clusters and superclusters, which serve as regions where normal matter can gather and coalesce into complex systems. This interplay between dark and baryonic matter is key to understanding cosmic evolution.
• Evaluate the significance of gravitational lensing in providing evidence for dark matter's existence and distribution across the universe.
  • Gravitational lensing is significant because it offers direct evidence for dark matter's existence and its distribution. When light from distant galaxies passes near massive objects like galaxy clusters, the light bends due to gravity—a phenomenon predicted by Einstein's theory of general relativity. By analyzing how light bends around these masses, astronomers can infer the presence and amount of dark matter that is not directly visible. This technique has been essential in mapping dark matter's distribution in the universe and understanding its role in shaping cosmic structures.

Related terms

baryonic matter: The ordinary matter that makes up stars, planets, and living organisms, which constitutes only about 5% of the universe's total mass-energy content.

gravitational lensing: The bending of light from distant objects due to the gravitational field of a massive foreground object, providing evidence for the existence of dark matter.

cosmic microwave background: The afterglow radiation from the Big Bang, which provides critical information about the early universe and the distribution of dark matter.