Dark matter

Definition

Dark matter is a 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 shaping the universe's structure, influencing the formation of galaxies and the movement of celestial bodies. Understanding dark matter helps explain the distribution of mass in the cosmos and supports the Big Bang theory, which posits that the universe expanded from an extremely hot and dense state.

5 Must Know Facts For Your Next Test

1. Dark matter accounts for approximately 27% of the universe's total mass-energy content, while normal (baryonic) matter makes up about 5%.
2. It cannot be observed directly with telescopes, which is why its presence is inferred from gravitational effects on visible matter.
3. The concept of dark matter emerged from observations of galaxy rotation curves, which showed that galaxies spin at speeds that cannot be explained by visible mass alone.
4. Cosmic microwave background radiation provides evidence for dark matter through tiny temperature fluctuations that reflect density variations in the early universe.
5. Various experiments are ongoing to detect dark matter particles directly or indirectly, but so far, none have definitively succeeded.

Review Questions

• How does dark matter influence the formation and structure of galaxies?
  • Dark matter significantly impacts how galaxies form and evolve by providing the gravitational framework necessary for their structure. It creates gravitational wells that attract baryonic matter, leading to galaxy formation. The presence of dark matter explains why galaxies rotate at such high speeds without flying apart; there’s unseen mass that contributes to their gravitational pull.
• Discuss the role of dark matter in supporting the Big Bang theory.
  • Dark matter plays a pivotal role in supporting the Big Bang theory by influencing cosmic evolution and structure formation in the early universe. Observations such as galaxy cluster dynamics and cosmic microwave background fluctuations suggest that dark matter was essential in forming large-scale structures following the initial expansion. This evidence aligns with predictions made by cosmological models based on the Big Bang theory.
• Evaluate the implications of dark matter research for our understanding of the universe's composition and fate.
  • Research on dark matter has profound implications for our understanding of the universe’s composition, as it reveals that approximately 27% of the universe consists of this unseen material. This understanding challenges our conception of what constitutes mass and energy in the cosmos. Furthermore, studying dark matter helps scientists predict the universe's fate—whether it will continue to expand indefinitely or eventually collapse—by informing models on gravitational influences at cosmic scales.

Related terms

dark energy:

A mysterious force that is driving the accelerated expansion of the universe, thought to comprise about 68% of the universe's total energy content.

baryonic matter: The ordinary matter that makes up stars, planets, and living organisms, consisting of protons, neutrons, and electrons, constituting only about 5% of the universe.

gravitational lensing: A phenomenon where the gravity of a massive object, like a galaxy or cluster of galaxies, bends the light from objects behind it, allowing scientists to infer the presence of dark matter.