UNIVERSE (LOOSELEAF):STARS+GALAXIES
6th Edition
ISBN: 9781319115043
Author: Freedman
Publisher: MAC HIGHER
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Chapter 23, Problem 57Q
To determine
The way to distinguish star images from unresolved images of remote galaxies on a CCD.
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How astronomers determine the distance of a galaxy? Explain.
Question A1
a)
The Large Magellanic Cloud (LMC) is a galaxy in the vicinity of the Milky Way. It is at a
distance of 50 kpc, and has a size across of 9.86 kpc.
Consider a star similar to Vega (absolute magnitude M = 0.58) which is at the edge of the
LMC as seen on the sky. What is its apparent magnitude? Show your calculation.
b) A second similar star is observed near the centre of the LMC as seen on the sky with an
observed apparent magnitude of m = 20.3. Is this consistent with the star being a member
of the LMC? Explain your reasoning.
c) An observational study has derived a map of the extinction Ay across the LMC, and shown
that its average value is 0.38, with a standard deviation of 0.57.
For the star discussed in part (b), if extinction is taken into account, does your conclusion
about the star's membership of the LMC change? Explain your reasoning. You may assume
that the star may suffer the full (positive) range of extinction found in the study of the LMC.
d) Which other…
A scientist, using a telescope, sees arcs of light around a galaxy. In 3–5 sentences, explain the cause of the arcs of light.
Chapter 23 Solutions
UNIVERSE (LOOSELEAF):STARS+GALAXIES
Ch. 23 - Prob. 1QCh. 23 - Prob. 2QCh. 23 - Prob. 3QCh. 23 - Prob. 4QCh. 23 - Prob. 5QCh. 23 - Prob. 6QCh. 23 - Prob. 7QCh. 23 - Prob. 8QCh. 23 - Prob. 9QCh. 23 - Prob. 10Q
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- Describe how you might use the color of a galaxy to determine something about what kinds of stars it contains.arrow_forwardWhy does the disk of a spiral galaxy appear dark when viewed edge on?arrow_forwardIf we see a double image of a quasar produced by a gravitational lens and can obtain a spectrum of the galaxy that is acting as the gravitational lens, we can then put limits on the distance to the quasar. Explain how.arrow_forward
- The center of a faint but active galaxy has magnitude 26. How much less bright does it look than the very faintest star that our eyes can see, roughly magnitude 6?arrow_forwardLook back at Figure 6.18 of Cygnus A and read its caption again. The material in the giant lobes at the edges of the image had to have been ejected from the center at least how many years ago? Figure 6.18 Radio Image. This image has been constructed of radio observations at the Very Large Array of a galaxy called Cygnus A. Colors have been added to help the eye sort out regions of different radio intensities. Red regions are the most intense, blue the least. The visible galaxy would be a small dot in the center of the image. The radio image reveals jets of expelled material (more than 160,000 light-years long) on either side of the galaxy. (credit: NRAO/AUI)arrow_forwardConsider the following data on four stars: Which star would have the largest radius? Which star would have the smallest radius? Which star is the most common in our area of the Galaxy? Which star is the least common?arrow_forward
- Assume that the Sun orbits the center of the Galaxy at a speed of 220 km/s and a distance of 26,000 lightyears from the center. A. Calculate the circumference of the Sun’s orbit, assuming it to be approximately circular. (Remember that the circumference of a circle is given by 2pR, where R is the radius of the circle. Be sure to use consistent units. The conversion from light-years to km/s can be found in an online calculator or appendix, or you can calculate it for yourself: the speed of light is 300,000 km/s, and you can determine the number of seconds in a year.) B. Calculate the Sun’s period, the “galactic year.” Again, be careful with the units. Does it agree with the number we gave above?arrow_forwardAt the average density of the interstellar medium, 1 atom per cm3, how big a volume of material must be used to make a star with the mass of the Sun? What is the radius of a sphere this size? Express your answer in light-years.arrow_forwardDescribe what a typical star in the Galaxy would be like compared to the Sun.arrow_forward
- Assume that dark matter is uniformly distributed throughout the Milky Way, not just in the outer halo but also throughout the bulge and in the disk, where the solar system lives. How much dark matter would you expect there to be inside the solar system? Would you expect that to be easily detectable? Hint: For the radius of the Milky Way’s dark matter halo, use R=300,000 light-years; for the solar system’s radius, use 100 AU; and start by calculating the ratio of the two volumes.arrow_forwardWhy didnt astronomers before Shapley realize how large our Galaxy is?arrow_forwardWhen comparing two isolated spiral galaxies that have the same apparent brightness, but rotate at different rates, what can you say about their relative luminosity?arrow_forward
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