29:50 MODERN ASTRONOMY
Fourth Homework Set...October 8, 1999
Note: Be sure to consult the Appendices in your book.
Having problems? Don't go around confused and despondent! Ask for help! The purpose
of these problem sets is to help you learn something.
(1) What is the escape speed from a neutron star with a mass of 1 solar mass
(1 
)?
meters/sec.
(2) Calculate the Schwarzschild Radius of a Black Hole with a mass of 
.
meters = 0.0197 astronomical units.
(3) A low mass star is orbiting a degenerate object. The radius of the orbit is
kilometers, and the orbital speed is 230 kilometers per second. Discuss
the possibilities of what the degenerate object might be, i.e. white dwarf, neutron star,
or black hole.
The mass is 1.4 . This is probably a neutron star, because it is
right at the maximum possible mass of a white dwarf. It is well below the estimated
maximum mass for a neutron star, so we need not conclude that it is a black hole.
(4) One of the solar analog stars I discussed in class is HD 20439. It has an
apparent magnitude of 7.80. Roughly how far away is it?
40 parsecs.
(5) In class I said that the amount of energy released in a supernova explosion is
about equal to the energy radiated by the Sun over its entire main sequence lifetime.
How would you quantitatively confirm this statement (or alternatively, show that I
was feeding you a line of baloney)?
Take luminosity of Sun 
Watts and multiply by 10 billion
years 
seconds = 
Joules, which is the energy
released in a supernova explosion.
(6) Look at Appendix 12 of your textbook. Which of the stars given there might plausibly
become a supernova in the near future?
Rigel, Betelgeuse, Acrux, Deneb, Beta Crucis.