Components of the Milky WayComponents of the Milky Way

The light from galaxies is centrally concentrated. But is the mass also centrally concentrated?

Does Mass follow Light in Galaxies?

Examples of Rotation CurvesExamples of Rotation Curves

Expected Versus ObservedExpected Versus ObservedRotation Curves for Our GalaxyRotation Curves for Our Galaxy

The Maybe Correct Way to Think The Maybe Correct Way to Think about Our Galaxyabout Our Galaxy

The “Mass Size of the Galaxy is 10 times larger (1000 times more volume) than the “Light Size” of the galaxy this seems weird?

Shouldn’t there be “DarkGalaxies” appearance of light (baryons) in the DM halo is random?

Dark Matter in M31 – Flat Dark Matter in M31 – Flat Rotation CurveRotation Curve

Dark Matter in Other Spiral Dark Matter in Other Spiral Galaxies – Flat Rotation CurvesGalaxies – Flat Rotation Curves

NGC 3198

Dark Matter in Elliptical Galaxies – Dark Matter in Elliptical Galaxies – Evidence from X-ray GasEvidence from X-ray Gas

NGC 4697 opticalNGC 4697 Chandra

X-ray Evidence for Dark Matter in X-ray Evidence for Dark Matter in Clusters of GalaxiesClusters of Galaxies

Need enough gravityto keep the X-ray gasfrom “boiling off” intointergalactic space.

Possible Dark-Matter CandidatesPossible Dark-Matter CandidatesDark Matter is material that emits low light per unit mass

Galaxy Motions in a Cluster of GalaxiesGalaxy Motions in a Cluster of Galaxies

The Coma Cluster

What about ordinary low mass stars: Clearly ruled out by What about ordinary low mass stars: Clearly ruled out by Space Telescope observations. Left picture shows Space Telescope observations. Left picture shows simulation if these stars dominate stellar clusters at the level simulation if these stars dominate stellar clusters at the level required for being DM candidates required for being DM candidates observations strongly observations strongly fail to confirm their existence at the required number fail to confirm their existence at the required number density.density.

Gravitational Lensing in Abell 2218Gravitational Lensing in Abell 2218

Gravitational MicrolensingGravitational Microlensing

Microlensing Light CurvesMicrolensing Light Curves

Length of the lensing event is determined by the mass of the lensing object.

Wimps: Weakly Interacting Massive Particles left Wimps: Weakly Interacting Massive Particles left over from early big bang now filling the Universeover from early big bang now filling the Universe

Dark matter elastically scatters off nuclei

Nuclear recoils detected by phonons, scintillation, ionization, …, …

e,

DM

Attisha

Three Real ChoicesThree Real Choices

DM is baryonic DM is baryonic most likely ruled out most likely ruled outDM is a particle DM is a particle hasn’t been detected hasn’t been detected despite 30 years of experiments and despite 30 years of experiments and expectation that detection is just around th expectation that detection is just around th corner.corner.Maybe its gravity that is broken (covered Maybe its gravity that is broken (covered in the third homework assignment).in the third homework assignment).Until DM is actually detected, it remains Until DM is actually detected, it remains just like an epicycle.just like an epicycle.