YSS - Intro. to Observational Astrophysics (ASTR 205)

Class #13Dark Matter, Dark Energy, and the

Fate of the Universe(Chapter 16)

Professor: José Maza

July 5, 2011

Dark Matter Dark Energy

Dark matter is the name given to mass that we infer to exist through its gravitational effects but that emits no detectable radiation.

Dark energy is the name given to an unseen influence that may be causing the expansion of the Universe to accelerate with time.

Evidence for dark matter

Distribution of mass in the Milky Way

A rotation curve plots the orbital speeds of objects in a galaxy against their distances from the center of the galaxy.

The flatness of the Milky Way’s rotation curve indicates that a large amount of dark matter lies beyond our galaxy’s visible regions.

Dark Matter in Other Spiral galaxies.

Dark Matter in Elliptical Galaxies

Dark Matter in Clusters of Galaxies

Orbits of Galaxies in Clusters Hot Gas in Clusters

Gravitational lensing

What might dark matter be made of?

Baryonic dark matter Non-baryonic dark matter Ordinary Dark Matter: MACHOs (Massive Compact Halo

Objects)

Extraordinary Dark Matter

The dark matter in galaxies cannot be made of neutrinos, because these very low mass particles travel through the universe at enormous speeds and can easily escape a galaxy’s gravitational pull.

WIMPs (weakly interacting massive particles). WIMPs are subatomic particles so the “massive” in their nature is relative.

WIMPs are often called “cold dark matter” to set them apart from the fast moving neutrinos.

WIMPs could make up most of the mass of a galaxy or cluster of galaxies, but they would be completely invisible in all wavelengths of light.

WIMPS are like neutrinos but more massive.

Structure Formation

What is the role of dark matter in galaxy formation?

What are the largest structures in the Universe?