Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Chapter 18, Problem 45E
How much would you weigh if you were suddenly transported to the white dwarf Sirius B? You may use your own weight (or if don’t want to own up to what it is, assume you weigh 70 kg or 150 lb). In this case, assume that the companion to Sirius has a mass equal to that of the Sun and a radius equal to that of Earth. Remember Newton’s law of gravity:
and that your weight is proportional to the force that you feel. What kind of star should you travel to if you want to lose weight (and not gain it)?
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Let's compare the acceleration due to gravity at the surface of a Sun-like star to a white dwarf of similar mass. We know that the force of gravity comes from F= G*m_1*m_2/r^2 and that F = m * a from some of Newton's laws. As such, we know that the acceleration due to gravity is given by a_g = G*m/r^2.
With that in mind, let's say that we have a white dwarf star is approximately the size of the Earth which is 1/100 radius of the Sun (0.01 R Sun) and that the white dwarf has a mass that is approximately half the mass of the Sun (0.5 M_Sun). What is the ratio of the acceleration due to gravity at the surface of the white dwarf star (aka the surface gravity) compared to the surface gravity of the Sun-like star (assume its mass is 1 M_sun and radius is 1 R_Sun).?
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The Algol binary system consists of a 3.7 Msun star and a 0.8 Msun star with an orbital period of 2.87 days. Using Newton’s version of Kepler’s Third Law, calculate the distance, a, between the two stars. Compare that to the size of Betelgeuse (you’ll need to look that up).
Newton’s Version of Kepler’s Law: (M1 + M2) P2 = (4p2 /G) a3
Rearrange the equation to solve for a. Pi, p, is equal to 3.14. IMPORTANT NOTE: Google the value of G (the Universal Gravitational Constant) or look it up in your text. NOTICE THE UNITS. You must convert every distance and time in your equation to the same units, otherwise, you’ll get an incorrect answer. That means you must convert distances to meters, solar masses to kilograms, and time to seconds. When you compare your value to the size of Betelgeuse, it will also help that they are in the same units.
Chapter 18 Solutions
Astronomy
Ch. 18 - How does the mass of the Sun compare with that of...Ch. 18 - Name and describe the three types of binary...Ch. 18 - Describe two ways of determining the diameter of a...Ch. 18 - What are the largest- and smallest-known values of...Ch. 18 - You are able to take spectra of both stars in an...Ch. 18 - Sketch an HR diagram. Label the axes. Show where...Ch. 18 - Describe what a typical star in the Galaxy would...Ch. 18 - How do we distinguish stars from brown dwarfs? How...Ch. 18 - Describe how the mass, luminosity, surface...Ch. 18 - One method to measure the diameter of a star is to...
Ch. 18 - We discussed in the chapter that about half of...Ch. 18 - Is the Sun an average star? Why or why not?Ch. 18 - Suppose you want to determine the average...Ch. 18 - Why do most known visual binaries have relatively...Ch. 18 - Figure 18.11 shows the light curve of a...Ch. 18 - There are fewer eclipsing binaries than...Ch. 18 - Within 50 light-years of the Sun, visual binaries...Ch. 18 - Which is easier to observe at large distances-a...Ch. 18 - The eclipsing binary Algol drops from maximum to...Ch. 18 - Review this spectral data for five stars. Which is...Ch. 18 - Which changes by the largest factor along the main...Ch. 18 - Suppose you want to search for brown dwarfs using...Ch. 18 - An astronomer discovers a type-M star with a large...Ch. 18 - Approximately 6000 stars are bright enough to be...Ch. 18 - Use the data in Appendix J to plot an HR diagram...Ch. 18 - Use the diagram you have drawn for Exercise 18.25...Ch. 18 - Use the data in Appendix I to plot an HR diagram...Ch. 18 - If a visual binary system were to have two...Ch. 18 - Two stars are in a visual binary star system that...Ch. 18 - Describe the spectra for a spectroscopic binary...Ch. 18 - Figure 18.7 shows the velocity of two stars in a...Ch. 18 - You go out stargazing one night, and someone asks...Ch. 18 - If you were to compare three stars with the same...Ch. 18 - Are supergiant stars also extremely massive?...Ch. 18 - Consider the following data on four stars: Which...Ch. 18 - If two stars are in a binary system with a...Ch. 18 - It is possible that stars as much as 200 times the...Ch. 18 - The lowest mass for a true star is 1/12 the mass...Ch. 18 - Spectral types are an indicator of temperature....Ch. 18 - We can estimate the masses of most of the stars in...Ch. 18 - In Diameters of Stars, the relative diameters of...Ch. 18 - Now calculate the radius of Sirius’ white dwarf...Ch. 18 - How does this radius of Sirius B compare with that...Ch. 18 - From the previous calculations and the results...Ch. 18 - How much would you weigh if you were suddenly...Ch. 18 - The star Betelgeuse has a temperature of 3400 K...Ch. 18 - Using the information provided in Table 18.1, what...Ch. 18 - Confirm that the angular diameter of the Sun of...Ch. 18 - An eclipsing binary star system is observed with...Ch. 18 - If a 100 solar mass star were to have a luminosity...Ch. 18 - If Betelgeuse had a mass that was 25 times that of...
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