Dark matter

Definition

Dark matter is a mysterious form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter. It plays a crucial role in the formation and evolution of galaxies, influencing their structure and motion while accounting for about 27% of the universe's total mass-energy content.

5 Must Know Facts For Your Next Test

1. Dark matter cannot be observed directly because it does not interact with electromagnetic forces, which means it doesn't emit light or other forms of radiation.
2. Its presence is inferred from gravitational effects on visible objects, such as the rotation curves of galaxies, which show that stars at the outskirts move faster than expected.
3. The majority of galaxies are surrounded by dark matter halos, which helps to bind them together and stabilize their structures over time.
4. Current estimates suggest that dark matter constitutes about 27% of the total mass-energy content of the universe, while ordinary matter accounts for only about 5%.
5. The search for dark matter continues with various experiments and observations aiming to identify its nature, as understanding it is essential for a complete picture of cosmic evolution.

Review Questions

• How does dark matter influence the motion and structure of galaxies?
  • Dark matter has a significant impact on how galaxies form and evolve. Its gravitational pull helps bind galaxies together, affecting their rotation speeds and overall stability. Observations show that stars in galaxies rotate at speeds that suggest there is much more mass present than what we can see; this unseen mass is attributed to dark matter. By stabilizing galaxies against gravitational collapse, dark matter plays a crucial role in shaping their structure.
• Discuss the evidence for dark matter as inferred from galactic rotation curves and gravitational lensing.
  • Evidence for dark matter primarily comes from observations of galactic rotation curves, which reveal that stars on the outskirts of galaxies rotate at unexpectedly high speeds compared to predictions based solely on visible mass. This discrepancy indicates that additional unseen mass must be present, attributed to dark matter. Furthermore, gravitational lensing effects observed in galaxy clusters provide another line of evidence; the bending of light from distant objects indicates mass that cannot be accounted for by visible matter alone.
• Evaluate the implications of dark matter's existence on our understanding of cosmic evolution and structure formation in the universe.
  • The existence of dark matter fundamentally alters our understanding of cosmic evolution and structure formation. Without dark matter, the universe would lack the necessary gravitational framework to form large-scale structures like galaxies and galaxy clusters within the time frame predicted by cosmological models. Dark matter influences not only how these structures form but also their interactions over cosmic time. As a result, recognizing dark matter's role leads to a revised view of how the universe evolved since the Big Bang, highlighting its critical importance in astrophysics.

Related terms

gravitational lensing:

A phenomenon where the light from distant objects is bent around massive objects like galaxy clusters, providing evidence for the presence of dark matter.

baryonic matter: The type of matter that makes up stars, planets, and living organisms, which constitutes only a small fraction of the total mass in the universe compared to dark matter.

cosmic microwave background (CMB): The remnant radiation from the Big Bang, which provides crucial data about the early universe and supports the existence of dark matter through its influence on the large-scale structure.