ASTRO 301/ 46690/ HOMEWORK 8
   
                          MONDAY APR 25 2005
  
                DUE BACK ON MONDAY MAY 2, 2005 BY NOON.
              
Note: The number of points for each question is indicated in brackets.

1a. WIMPS are some of the candidates for non-baryonic dark matter. 
    Gives two properties of WIMPS that make them hard to detect.   [2x2=4]

1b. Describe one future experiment which will help to characterize 
    WIMPS and how it plans to achieve its goal			   [3]
   
1c. Gravitational lensing is used to estimate the total mass in a 
    cluster of galaxies. Explain how gravity can bend light, given 
    that gravity acts on mass. Why can this method not be used to 
    estimate the mass of all nearby galaxy clusters?	      	   [3+3=6]
    

2a. What are major mergers and minor merger of spiral galaxies?    [2x3=6]
    Describe how the end products differ in these two types of
    mergers.


2b. The relative number of ellipticals compared to spirals often rises 
    near the center of galaxy clusters, as compared to non-cluster 
    environments. Explain why.					    [3]

2c. The relative number of spirals with disks that are devoid of gas 
    and star formation (Sa type disks) compared to those with disks 
    that have plenty of gas and star formation (Sc type disks) rises
    near the center of galaxy clusters, as compared to non-cluster 
    environments. Explain why.					    [4]

2d. In the center of some elliptical galaxies, astronomers find a 
    fast-rotating disk-like configuration of stars. One possibility
    is that the elliptical galaxy accreted a small spiral galaxy in
    during a recent minor merger, such that the disk of stars seen 
    in its center comes from the accreted spiral galaxy. Describe
    an observation which astronomers could carry out to further verify
    this hypothesis. Specify the wavelength at which you would carry
    this observation.						    [4]		
2e. The frequency of galaxy mergers was higher 12 Gyr ago than it is 
    today. Explain why						    [3]



3a. Describe two different interactions which our Galaxy, the Milky
    Way (an SBbc galaxy) is currently undergoing. (Do not use its 
    future impending interaction with  M31 as an example).	   [2+2=4]					 

3b. The Milky Way (an SBbc galaxy) is currently moving at 83 km/s 
    toward M31 (an SAb galaxy), which is located 2.5 million ly away. 
    What is the ratio of the luminosities of the Milky Way and M31,
    based on Table G of your book (Cosmic Perspectives, 3rd ed.)?  [3]
					  

3c. Assume that ratio of masses for M31 and the Milky way is the 
    same as the  ratio of their luminosities in 3c. If the Milky Way 
    merges with M31, will this be a major merger or a minor merger? 
    What is the likely fate of the Milky way after this merger?    [1+3] 

3d. How many seconds will it take before this merger happens? 
    Derive the answer by calculating how long it would take the 
    Milky Way to travel the distance separating it from  M31.
    Remember that travel time = distance/speed,and remember to 
    express quantities in the right units.		           [4]




4a. How long after the Big Bang was the hydrogen and helium we 
    see today in the Universe created?				   [2]	

4b. What is the era of recombination?				   [3]	
	
4c. Describes two piece of evidence for the Big Bang.		[2x2=4]	
	
4d. What is meant by the critical density of the Universe?	   [2]

4e. Describe the fates of the Universe if the density is above
    and below the critical density.				[2x3=4]

4f. What is inflation?  Describe two puzzling properties of	[3x2=6]
    the Universe that the inflation model can explain.