Dark matter halo

Definition

Dark matter halo is a theoretical, spherical region surrounding galaxies, including the Milky Way, composed mostly of dark matter. It extends beyond the visible components of the galaxy and contains most of its mass.

5 Must Know Facts For Your Next Test

1. Dark matter halos are essential for explaining the rotation curves of galaxies, which show that stars at the edges rotate as quickly as those near the center.
2. The existence of dark matter halos is inferred from gravitational effects on visible matter and radiation rather than direct observation.
3. Dark matter makes up about 85% of the total mass of the universe, with halos being significant contributors to this mass in galaxies.
4. Simulations of galaxy formation require dark matter halos to match observed structures and behaviors in real galaxies.
5. Gravitational lensing, where light from distant objects is bent by massive objects like dark matter halos, provides strong evidence for their existence.

Review Questions

• What role do dark matter halos play in explaining the rotation curves of galaxies?
• How is the presence of dark matter halos inferred if they cannot be directly observed?
• What percentage of a galaxy's mass is typically made up by dark matter?

Related terms

Galaxy Rotation Curve: The plot showing how orbital velocities vary with distance from a galaxy's center, often used to infer dark matter presence.

Gravitational Lensing: The bending of light from distant objects caused by massive bodies like dark matter halos.

Visible Matter: The portion of a galaxy's mass that emits electromagnetic radiation and can be directly observed.