NATS 1740 Chapter Notes - Chapter 16: Gravitational Lens, Spiral Galaxy, Orbital Speed

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Published on 13 Apr 2013
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Chapter 16 Dark Matter, Dark energy and the fate of the universe!
16.1 Unseen influences in the Cosmos
What do we mean by dark matter and dark energy?
Dark matter: is the name given to mass that emits no detectable radiation
We infer its existence from its gravitational effects
Dark energy: is the name given to the unseen influence that may be causing the
expansion of the universe to accelerate with time
16.2 Evidence for dark matter
Dark matter in the milky way
- Orbital speeds in the milky way remain high even very far from the center, indicating that
a large amount of dark matter lies beyond our galaxy’s visible regions
Rotation curve diagrams: summarize results of orbital measurements
Rotation curve means orbital speed increases with distance
Falling curve means orbital speed decreases with distance
Flat curve means orbital speed remains large at large distances
Dark matter in other galaxies
- Orbital speeds in the outer regions of other spiral galaxies indicate that they too harbor
lots of dark matter
What is the evidence for dark matter in clusters of galaxies?
- Observations suggest that the ratio of dark matter to luminous matter is even greater than
that in individual galaxies
Orbits of galaxies in clusters
- Fritz Zwicky one of first astronomers to think of galaxy clusters as huge swarms of
galaxies bound together by gravity
- The orbits of galaxies in clusters tell us that galaxy clusters contain huge amounts of dark
matter
Hot gas in clusters
- Temperature measurements of hot gas also tell us the amount of dark matter in clusters
and give results that agree with those we infer from galaxy velocities
Gravitational equilibrium: outward pressure balances gravity’s inward pull
Gravitational lensing
Gravitational lenses: bend light beams as they pass by
- Gravity’s light bending effects distort the images of galaxies lying behind a cluster,
enabling us to measure the cluster’s mass without relying on Newton’s laws
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Document Summary

Chapter 16 dark matter, dark energy and the fate of the universe! Dark matter: is the name given to mass that emits no detectable radiation. We infer its existence from its gravitational effects. Dark energy: is the name given to the unseen influence that may be causing the expansion of the universe to accelerate with time. Orbital speeds in the milky way remain high even very far from the center, indicating that a large amount of dark matter lies beyond our galaxy"s visible regions. Rotation curve diagrams: summarize results of orbital measurements. Rotation curve means orbital speed increases with distance. Falling curve means orbital speed decreases with distance. Flat curve means orbital speed remains large at large distances. Orbital speeds in the outer regions of other spiral galaxies indicate that they too harbor lots of dark matter. Observations suggest that the ratio of dark matter to luminous matter is even greater than that in individual galaxies.

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