Dark Matter Evidence Galaxies Quiz: Test Your Cosmic Knowledge

Concept: rotation curve meaning. Rotation curves plot orbital speed vs radius. They reveal whether mass is concentrated in the center or spread out in a halo.

Concept: gravity vs radius (qualitative). With most mass concentrated near the center, gravity weakens with distance. That would make outer orbits slower than observed.

Concept: flat curves imply extra mass. Constant speed far out suggests mass continues increasing with radius. That fits a large, extended dark matter halo.

Concept: gravitational lensing. According to relativity, mass curves spacetime and light follows curved paths. This lets us “weigh” objects using lensing.

Concept: strong lensing signatures. When alignment is good and mass is high, light paths split into multiple routes. This can create arcs, rings, or multiple images.

Concept: weak lensing maps. Weak lensing slightly distorts galaxy shapes. Averaging over many galaxies reveals the mass distribution.

Concept: cluster dynamics. The speeds of galaxies in a cluster indicate the total gravitational pull. Visible galaxies and gas are not enough to account for those speeds.

Concept: baryons in clusters. The hot intracluster gas is ordinary matter and can be measured. Even including it, total mass often appears larger than baryons alone.

Concept: extended mass. Lensing reveals total mass, not just luminous mass. It commonly shows halos extending beyond visible light.

Concept: mismatch. The gravitational effects observed are stronger than what visible matter predicts. This mismatch motivates dark matter or alternative gravity ideas.

Concept: gravity affects motion. Any mass contributes to gravitational pull. That changes orbital speeds, cluster motions, and lensing patterns.

Concept: halo vs stars. The evidence points to halos surrounding galaxies, not necessarily inside stars. Dark matter affects the galaxy’s overall gravitational field.

Concept: total mass measurement. Lensing depends on gravity, which depends on mass-energy. It can reveal mass where little or no light is present.

Concept: converging evidence. Different methods have different biases. Agreement among them reduces the chance it’s just an error in one technique.

Concept: mass estimation tools. Dynamics, lensing, and gas physics all provide mass clues. Sound is not the method used for galaxy mass.

Concept: enclosed mass idea. Faster-than-expected speeds suggest more mass is present farther out. This is consistent with an extended halo.

Concept: scale of evidence. Dark matter doesn’t strongly interact with light or ordinary matter in daily life. Its gravitational effects show up most clearly at large scales.

Concept: weak interaction. If dark matter barely collides with atoms, detectors see very few events. That is consistent with why it has remained elusive.

Concept: penetrating nature. A weakly interacting particle could pass through matter without being stopped. That’s why detection experiments must be extremely sensitive.

Concept: gravity-based measurement. Rotation curves and lensing are both driven by gravity. They point to mass distribution even where little light is present.