Dark matter halos

Definition

Dark matter halos are large, invisible structures composed primarily of dark matter that surround galaxies and galaxy clusters, providing the necessary gravitational pull to hold visible matter together. These halos play a vital role in shaping the cosmic web, influencing the formation of filaments and sheets while also creating vast voids between them. Understanding dark matter halos helps explain how galaxies form and evolve within the larger structure of the universe.

5 Must Know Facts For Your Next Test

1. Dark matter halos are thought to be roughly spherical in shape and can extend far beyond the visible boundaries of galaxies.
2. The mass of dark matter halos can be estimated through their gravitational effects on nearby visible matter and light, revealing that they often contain much more mass than is seen in stars and gas.
3. Dark matter halos play a critical role in the process of galaxy formation, as they provide the gravitational wells where baryonic matter can accumulate and form stars.
4. Simulations of cosmic structure formation show that dark matter halos are essential for explaining the observed distribution of galaxies in the universe, influencing their clustering and movement.
5. The study of dark matter halos has led to important insights about the composition of the universe, suggesting that dark matter constitutes about 27% of its total energy density.

Review Questions

• How do dark matter halos contribute to the structure of the cosmic web?
  • Dark matter halos are crucial for forming the cosmic web's intricate structure by acting as gravitational centers around which galaxies gather. They create dense filaments that connect clusters of galaxies while simultaneously defining vast voids where little visible matter exists. This gravitational influence ensures that galaxies are not randomly distributed but instead follow a pattern that mirrors the presence of these invisible structures.
• Discuss the implications of dark matter halos on our understanding of galaxy formation and evolution.
  • Dark matter halos fundamentally shape our understanding of galaxy formation by providing the gravitational environment necessary for baryonic matter to accumulate. As these halos grow over time through merging and accretion, they allow galaxies to form within them, leading to diverse evolutionary paths. This connection highlights how the unseen mass of dark matter directly influences visible cosmic structures and their behaviors over cosmic time.
• Evaluate how observations related to dark matter halos have influenced current theories about the composition of the universe.
  • Observations of dark matter halos have significantly impacted our understanding of cosmic composition by revealing a discrepancy between visible mass and total mass inferred from gravitational effects. The existence and distribution of these halos support theories that posit dark matter as a major component of the universe's total energy density. This has prompted a reevaluation of existing models, leading to broader acceptance of dark energy and revised estimates regarding the proportions of baryonic versus non-baryonic matter in the cosmos.

Related terms

gravitational lensing: The bending of light from distant objects due to the gravitational field of a massive object, like a dark matter halo, allowing astronomers to infer the presence and distribution of dark matter.

cosmic web: The large-scale structure of the universe, characterized by a network of filaments and sheets made up of galaxies and dark matter, with vast empty voids in between.

baryonic matter: The ordinary matter that makes up stars, planets, and living organisms, as opposed to dark matter which does not emit or absorb light.