Cosmology Review Problems

Cosmology Review Problems

  1. Suppose a large amount of weakly interacting massive particles lie between us and a distant galaxy. How will our view of the distant galaxy be a ected?
  2. Below is an actual rotation curve of a galaxy (graph from 1989A&A…223…47B) a)Draw the expected rotation curve.

b)If a galaxy had a rotation curve as \expected”, what would that indicate about the mass enclosed in a galaxy?

c)A galaxy like the Milky Way has a mass/light ratio of about 10. What does that imply?

3. Recall that lensing causes arc-like structures to appear when we view distant objects.

a)Sketch what is happening.

b)Would more mass produce a stronger lensing e ect, or a weaker one, and why?

4. The current value of the Hubble parameter is about H = 70 km/s/Mpc. If it were to turn out we were wrong, and the value is twice that, what are the implications?

5. The graph below shows possible futures for the Universe. The data points are from type 1a supernovae.

a)Why do astronomers use type 1a supernovae and not also type II? b)From the graph, which models show a currently expanding Universe? c)Which models predict an expanding Universe in the far future? d)Which model is the mostly strongly supported and why?

d)What is the critical density of a \coasting” Universe?

6. Below is a graph that shows our current accelerating Universe.

a)What might a decelerating Universe look like? Sketch.

b)What might a coasting Universe look like? Sketch.

c)What is causing the acceleration and what might it be?

 

 

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