| Homework 1 | Homework
2 | Homework 3 | Homework
4 | Homework 5 | Homework
Due Tuesday, April 17, 2001.
- Attempt all questions in Part A and
1 of the questions in Part B. Please write all answers to Part
A on these sheets.
- With a few exceptions, Part B questions
call for a paragraph of coherent English. Points will be deducted
if your sentences are incomplete and reduced to a list of items
or a phrase or two. Do not, however, pad your answers by rewriting
the question, by rewriting one sentence in several different
Review session: Monday, April 6, 5-6pm,
A1. Which of the following lists
the remnants of stellar evolution in order of decreasing maximum
a. neutron star, white dwarf, black hole
b. black hole, neutron star, white dwarf
c. white dwarf, black hole, neutron star
d. black hole, white dwarf, neutron star
e. They all have approximately the same mass.
A2. In AD 1054, Chinese astronomers observed
the appearance of a new star. Its location is now occupied by
a. a supernova remnant
b. a pulsar
c. a neutron star
d. all of the above
e. none of the above
A3. What kind of "corpse" will
be left at the end of the Sun's life?
A4. As a massive star collapse, the gravitational
field on the stellar surface
b. increases strongly
c. decreases with the square of decreasing size
d. remains the same
A5. The Schwarzschild radius of a black
a. the radius of the star when it is on the main sequence.
b. the distance from a black hole inside of which light cannot
c. the theoretical size of the smallest possible white dwarf.
d. the size of a star when it begins hydrogen burning just prior
to reaching the main sequence.
e. the size of the early protosun.
A6. Suppose you wish to search for low-mass
main sequence stars using a space telescope. Will you design
telescope to detect light in the ultraviolet or the infrared
part of the spectrum? Why?
A7. Of the following stages of evolution,
pick out those that the Sun has experienced or probably will
List them in the order in which they occur.
A8. Of the following stages of evolution,
pick out those that a 20 M star will experience.
List them in the order in
which they occur.
|Supernova Type Ia
|red super giant
||supernova Type II
A9. What is the Chandrasekhar limit?
A10. As observed from Earth, it often happens
that only the brightest stars in a cluster are observable.
- What type of stars will these be in a very young cluster?
- In a very old one?
A11. The diagrams show brightness
- spectral type diagrams for 2 open clusters.
is 200 parsecs from us, how far is cluster ?
Answer in parsecs.
A12. The solar system is located within
a. the galactic halo
b. the galactic disk
c. the galactic nucleus
d. none of the above; the solar system is not located in a galaxy.
A13. Astronomers of the 18th and 19th centuries
thought that the Sun was near the center of the Milky Way galaxy
since they counted the same number of stars in the disk of the
Galaxy in every direction.
The reason they were not correct is the
- is an irregular galaxy with a chaotic
- contains dust that obscures its distant
- has the shape of a tube with the Sun near
- has two kinds of Cepheid variables, so
that all distance measurements until recently were incorrect
- has a giant black hole at its center
A14. The position of the Sun in the Galaxy
was determined by Shapley by measuring positions of
- galactic (open) clusters
- globular clusters
- T Tauri stars
A15. If the Sun is 5 billion years old,
how many times has it orbited the galaxy?
Show all work.
A16. Arrange the following in order of
||a 50 solar mass
A17. Arrange the following in order of
increasing average density:
- - the air in the classroom
- Sirius B
- the Crab Pulsar
- Sirius A
a. Describe how a white dwarf is produced
from a red giant.
b. Why have none of the white dwarfs we see been produced by
the deaths of the lowest mass
(M< 0.4M) stars?
c. White dwarfs are the commonest stars in the Galaxy. Not one
of the 6000 stars visible to the naked eye is a white dwarf.
Explain why the second statement is not inconsistent with the
a. Describe two key observed differences
between Supernovae of Type Ia and II.
b. In a spiral galaxy, supernovae occur at the rate of 1 every
100 years. If you were given access to a small telescope, describe
how you would check this estimate.
c. Our Galaxy is a typical spiral galaxy. The last recorded supernovae
occurred about 300 years ago. We would expect several supernovae
to have exploded in the last 300 years. How is it possible to
miss so many so close (the Galaxy is a mere 40 kpc in diameter)
a. Describe why a massive star develops
an onion skin structure (see diagram from Seeds Fig. 14-8)
before finally exploding.
b. Explain why an iron core marks the end of a massive star's
c. Betelgeuse, a red giant, supergiant, is a massive star in
the constellation of Orion. Why do you think it quite likely
that Betelgeuse is burning He in its core?
a. Describe a neutron star. Include remarks
on the mass, radius, and composition of such a star.
b. What do we mean when we say "Every pulsar is a neutron
star, but not every neutron is an observable pulsar"?
c. Why is there an upper limit to the mass of neutron stars?
And why is that upper limit not well known?
a. Describe a 10M black hole.
Why do we say its 'black'?
b. What do we mean when we say 'Black holes have no hair'?
c. Describe how black holes are detected in our Galaxy. Be sure
that your description is consistent with the fact that light
cannot escape from a black hole. Also explain why the observations
you describe point to a black hole rather than a neutron star
or a white dwarf.
a. Main sequence stars are referred to
as 'metal-poor.' What is meant by the words 'metal' and 'metal-
b. Young main sequence stars are referred to a 'metal-rich' or
as having roughly the same metal content as the Sun.
Explain why our Galaxy contains both metal-rich and metal-poor
M-type main sequence stars, but NO metal-poor O-type main sequence
stars. All the O-type main sequence stars are metal-rich.
c. Discuss one piece of observational evidence in support
of the idea that stars synthesize metals.
a. How is the 21 cm line of hydrogen produced
by interstellar clouds of cold hydrogen gas?
b. Suppose you had access to a radio telescope with high angular
resolving power. Describe how you would determine the speed and
rotation of a nearby and well-resolved spiral galaxy.
c. Spiral galaxies contain large amounts of dark matter. Suppose
you observed a spiral galaxy that had no dark matter and another
that, like our Galaxy, had substantial amounts of dark matter.
How would you distinguish the two through observation of their
speed of rotation?
Syllabus | Homework 1 | Homework 2 | Homework
3 | Homework 4 | Homework
5 | Homework 6