Massive compact halo objects

Definition

Massive Compact Halo Objects (MACHOs) are a type of dark matter candidate that includes objects like black holes, neutron stars, and brown dwarfs. They are hypothesized to reside in the halos of galaxies and contribute to the overall mass without emitting significant light.

5 Must Know Facts For Your Next Test

1. MACHOs are considered one possible explanation for the missing mass in galaxies, contributing to dark matter.
2. They can be detected through gravitational lensing, where they bend light from more distant stars.
3. MACHOs differ from WIMPs (Weakly Interacting Massive Particles), another dark matter candidate, in that MACHOs are composed of ordinary baryonic matter.
4. Searches for MACHOs have been conducted using microlensing surveys, which monitor many stars for temporary brightness increases.
5. The abundance of MACHOs is still uncertain; however, current evidence suggests they cannot account for all dark matter.

Review Questions

• What types of objects are included under Massive Compact Halo Objects?
• How can MACHOs be detected if they do not emit significant light?
• Explain how MACHOs differ from WIMPs in terms of their composition.

Related terms

Gravitational Lensing: A phenomenon where a massive object bends the light from a more distant object, often used to detect dark matter.

Weakly Interacting Massive Particles (WIMPs): A hypothetical particle that is another leading candidate for dark matter; unlike MACHOs, WIMPs interact via weak nuclear force and gravity.

Microlensing: A method used to detect MACHOs by observing the temporary increase in brightness of a background star caused by the gravitational field of a foreground object.