Physics PHYS 141

Cosmology

Problem Set #3

 

After you finish this problem set, you should be familiar with:

planetary nebulae

AGB stars

white dwarfs

protostars

OB associations

neutron stars

Helium Burning

globular clusters

pulsars

Variable Stars

metal rich/poor clusters

black hole

Metal Rich/Poor Clusters

cepheid variables

singularity

novae

RR Lyrae variables

event horizon

 

Please answer the following questions using sentences and paragraphs.  When it is helpful, please use diagrams and equations.

  1. Are stars still forming today? How do we know? Where would they be most likely found?
  2. Explain the different stages that occur in the core of a massive star, that is, a star with more than 8 times the mass of the Sun. What elements are fused together in the core at different times in a massive starís life? What is the final state of the star?
  3. Speculate about the connection between stars that produce carbon and oxygen in their cores by "burning" helium, and the existence of life on Earth. Remember that life on Earth is carbon and oxygen based. How does this connection relate to the Genesis description of the creation of life?
  4. What kinds of observations might you make to locate and identify black holes?
  5. In you own words, describe what would you experience as you flew toward a black hole. To see more information, you could look at http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.htm and http://jila.colorado.edu/~ajsh/insidebh/intro.html.
  6. What are the parts of a black hole. Explain the "no hair" theorem.
  1. Draw and explain an H-R diagram. Be sure to sketch the regions occupied by protostars, main sequence stars, red giants, and white dwarfs, and any other regions you think may be important.
    1. Explain why the H-R diagram is so important in astronomy.
    2. Can an HR diagram be used to distinguish between protostars and red giants? How do astronomers distinguish between them?
    3. Watch the animation of the life of a massive star (that is, a star with 5 times the mass of the Sun) on the HR diagram at right. You might have to click on refresh to start the animation over. Describe the different stages. What elements are fused together in the core at different times in a massive starís life? What is the final state of the star?
    4. How does the development of a star like the Sun differ from that of a more massive star, like the one above?
    5. Explain how and why the turnoff point on the HR diagram of a cluster is related to the clusters age.
       
    6. How old is the globular cluster M12?  The HR diagram for this cluster is shown below.  Why is it okay to use apparent rather than absolute magnitude in this case?
  1.  What is a galaxy? Briefly describe the geometry of the major types of galaxies. Describe the distributions of stars, gas, and dust in each type. Draw a diagram of a spiral galaxy, labeling the important regions.
  2. The Milky Way is our home galaxy. Why do we see the Milky Way as a band of faint light around the sky? 
  3. Describe the Shapley-Curtis debate. Explain how Edwin Hubble proved that M31, the Andromeda "Nebula", is not a nebula at all. What did Hubble prove about M31?
     
  4. Describe the nucleus of the Milky Way galaxy.  Is there any evidence that might indicate the presence of a supermassive black hole at the core of our galaxy?
     

 

Here are some practice "figure it out rather than memorize" type questions.  They will not be graded as part of the homework (so don't turn them in), but they may be useful as you prepare for the test. 

1.

How much time does it take for a 3-solar-mass protostar to finish accreting mass from the interstellar cloud?

 

A)

about 100,000 years

 

B)

about 1 billion years

 

C)

about 1 million years

 

D)

about 10,000 years

 

2.

How long does it take for a 2-solar-mass star to pass through the preĖmain-sequence phase?

 

A)

about 500,000 years

 

B)

about 10 billion years

 

C)

about 10 million years

 

D)

about 10,000 years

 

3.

During helium burning, some 4He combines with 16O, much like the way it combines with 12C to form 16O.  What is produced by the 16O + 4He reaction? 

 

A)

20F (heavy isotope of fluorine)

 

B)

22Na (light isotope of sodium)

 

C)

18O (heavy isotope of oxygen)

 

D)

20Ne (regular isotope of neon)

 

4.

If the universe was only 100 million years old, which of the following groups of stars would have never moved beyond the main sequence?

 

A)

Stars with masses greater than 10 solar masses

 

B)

Stars with masses less than 0.08 solar masses

 

C)

Stars with masses less than 3 solar masses

 

D)

Stars with masses greater than 100 solar masses

 

5.

Suppose that, when the stars in a particular open star cluster are plotted in a Hertzsprung-Russell diagram, the turnoff point is at an absolute magnitude of +3. What is the approximate age of this cluster?

 

A)

500 million years

 

B)

4 billion years

 

C)

1 billion years

 

D)

100 million years

 

6.

What happens to the Schwarzschild radius of a black hole if you double the amount of mass in the black hole?

 

A)

The Schwarzschild radius decreases by a factor of 4.

 

B)

The Schwarzschild radius is quadrupled (4 times).

 

C)

The Schwarzschild radius is halved.

 

D)

The Schwarzschild radius is doubled.

 

 7.

A Cepheid variable star with a pulsation period of a few days is seen in the spiral arm of a galaxy. Its apparent brightness is measured as 104 times fainter than an equivalent star 1000 ly away from the Sun in our Galaxy. Assuming no light absorption between galaxies, what is the distance to the far Cepheid and hence to the galaxy?

 

A)

107 ly (104 times farther away)

 

B)

10,000 ly (10 times farther away)

 

C)

10 ly (100 times closer)

 

D)

100,000 ly (100 times farther away)

 

8.

On the basis of the distance to the Coma cluster of galaxies and the Hubble relation (using an intermediate value of the Hubble constant H0 equal to 80 km/s per million parsecs; see Fig. 16-20, Comins and Kaufmann, Discovering the Universe, 7th Ed.), what would be the approximate wavelength shift of the Balmer Hspectral line at 656.3 nm emitted by a galaxy in the cluster because of the general expansion of the universe? (See also Astronomer's Toolbox 16-1 of Comins and Kaufmann, Discovering the Universe, 7th Ed.)

 

A)

1.61 nm

 

B)

161.0 nm

 

C)

1.61 ◊ 106 nm

 

D)

16.1 nm

  

9.

One astronomer (astronomer A) claims that the Hubble constant is 84 km/s per Mpc, while another (astronomer B) claims that it is 63 km/s per Mpc. If, based on the Hubble constant, astronomer A claims that a particular galaxy is 4 billion ly away, then astronomer B would claim that it is

 

A)

3 billion ly away.

 

B)

5.3 billion ly away.

 

C)

6 billion ly away.

 

D)

2 billion ly away.