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Astronomy 120
HOMEWORK - Chapter 16
Stardeath
Use a calculator whenever necessary.
For full credit, always show your work and explain how you got your answer.
Be careful about units!
Please CIRCLE or put a box around your final answer if it is numerical.
1. Zeilik Study Exercise 16.1
In a short paragraph, describe the primary characteristics of a white dwarf?
2. Zeilik Study Exercise 16.2
In a short paragraph, describe to a friend who has not studied astronomy the chief features of
a neutron star.
3. Zeilik Study Exercise 16.5
Assuming no loss of mass, what will be the final form of
a) a 0.5-solar-mass star
b) a 2-solar-mass star?
4. Zeilik Study Exercise 16.3
What observational evidence do we have for the actual existence of neutron stars and white
dwarfs?
5. Zeilik Study Exercise 16.10
What one feature of pulsars links them most strongly to rapidly rotating neutron stars?
6. Zeilik Study Exercise 16.11
What is the source of the electromagnetic radiation in the pulses of pulsars?
7. Zeilik Study Exercise 16.6
Make a list of the observational evidence that supports the idea of the Crab Nebula as a
supernova remnant.
8. Zeilik Study Exercise 16.8
If a black hole is really black, how can it be an x-ray source?
9. Zeilik Study Exercise 16.9
Why can’t you find out what happens inside a black hole?
10. Zeilik Study Exercise 16.4
Look around you. Of the items you see, what would not there if supernovas didn’t occur?
11. The Ring Nebula in Lyrae is a planetary nebula with an angular diameter of 72 seconds of arc
at a distance of 5000 ly.
a) What is its linear diameter?
b) If the Ring Nebula is expanding at a velocity of 15 km/sec, typical of planetary nebulae,
how old is it? Assume a uniform rate of expansion.
12. Zeilik 16.1.
a) Calculate the escape velocity from a solar-mass neutron star with a radius of 10 km.
b) Do the same thing for a solar-mass, white dwarf star with a radius of 7000 km.
13. Imagine a brown dwarf with a temperature of 1500 K and a radius of 0.1 the sun's radius. If it
radiates like a black-body, what would its luminosity be?
You will need to make use of the equation for flux:
F  Teff 4
where F is the flux emitted by a star if...
 is the Stefan-Boltzmann constant  5.6697  10 8 W m2  K 4
Teff is the surface temperature of the star
Then, once you know the flux, Use L  4r 2  F to find the luminosity, where r is the star's
radius.
14. You can calculate the Schwarzschild radius for a black hole of mass M. It is a conservation of
energy argument.
a) Set the kinetic energy equal to the potential energy and solve for the Schwarzshild radius r.
b) What would the Schwarzshild radius be if the sun suddenly became a black hole?