Dark matter

Definition

Dark matter is a mysterious and invisible substance that makes up about 27% of the universe's total mass-energy content. Unlike ordinary matter, it does not emit, absorb, or reflect light, making it undetectable by traditional means. Dark matter plays a crucial role in the formation and structure of galaxies and the overall dynamics of the universe, influencing how galaxies rotate and cluster together.

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 detected by conventional means.
2. The evidence for dark matter comes from observing the gravitational effects it has on visible matter, such as galaxies and galaxy clusters.
3. Galaxies rotate at such speeds that they would fly apart if only visible matter were present; dark matter provides the extra gravitational pull needed to keep them intact.
4. Observations of the cosmic microwave background radiation show variations that suggest dark matter influenced the early universe's structure.
5. Dark matter helps explain why galaxies are distributed in the universe as they are, clustering together in large structures rather than being uniformly spread out.

Review Questions

• How does dark matter influence the motion of galaxies and galaxy clusters?
  • Dark matter significantly impacts how galaxies rotate and interact within clusters. Galaxies rotate at high speeds, and without the additional mass contributed by dark matter, they would not have enough gravitational pull to hold together. Observations show that galaxies in clusters move faster than expected based on visible mass alone, indicating that dark matter must be present to account for this unseen mass and ensure stability within these cosmic structures.
• Discuss the role of gravitational lensing in providing evidence for the existence of dark matter.
  • Gravitational lensing occurs when light from a distant object is bent around a massive body, such as a galaxy or cluster of galaxies. This bending effect allows astronomers to infer the presence of dark matter in areas where we cannot see it directly. By studying how light is distorted from distant galaxies due to dark matter's gravitational influence, scientists can map out where dark matter resides and understand its distribution within the universe.
• Evaluate the implications of dark matter on our understanding of cosmic evolution and structure formation in the universe.
  • Dark matter fundamentally alters our understanding of how structures in the universe formed and evolved. Its presence explains why galaxies are clustered in certain patterns rather than being evenly distributed. Without dark matter, models of cosmic evolution would fail to account for observed phenomena like galaxy rotation curves and large-scale structure formation. Recognizing the role of dark matter has led to new theories about the universe's history and its ultimate fate, demonstrating its significance in cosmology.

Related terms

baryonic matter: The type of matter that makes up stars, planets, and living things, consisting of protons, neutrons, and electrons.

cosmic microwave background radiation:

The afterglow radiation from the Big Bang that fills the universe and provides evidence for the existence of dark matter through its effects on cosmic structure.

gravitational lensing: The bending of light from distant objects due to the gravitational influence of massive bodies like dark matter, allowing astronomers to infer its presence.