Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 24, Problem 30Q
To determine
The explanation for the appearance of galaxy
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Chapter 24 Solutions
Universe: Stars And Galaxies
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- 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…arrow_forwardThe figure below shows the spectra of two galaxies A and B.arrow_forwardFigure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…arrow_forward
- NGC 3379 is an El galaxy at a distance of 14.8 Mpc that has an apparent B band magnitude of 10.65 and a central velocity dispersion of 220 kms¬1. M87 is also an El galaxy, but lies in the Virgo cluster. M87 has a central velocity dispersion of 315 km s and an apparent B-band magnitude of 10.1. Assuming that both of these galaxies exactly follow the scaling relation that connects these properties, what is the distance to M87?arrow_forwardAn observational survey of distant galaxies is undertaken that involves measuring their distances using cepheid variables and red-shifts using spectroscopy. Explain how cepheid variables can be used to measure the distances to galaxies. A spectral line is observed whose wavelength in the laboratory is de length of this spectral line observed in each galaxy, Xo, is listed in the table, along with the distance, d, to the galaxy. Determine the red-shift and the recession velocity of each galaxy and tabulate your results by making a copy of the table and filling in the blank spaces. Sketch a Hubble diagram using your results and determine the value of the Hubble constant Ho in units of km s-1 Mpc. 650 nm. The wave- Galaxy 1 652.69 Galaxy 2 Galaxy 3 Galaxy 4 Galaxy 5 653.01 do (nm) d (Mpc) 658.54 662.18 681.63 17 19 54 77 200 v (km s-1)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 first clue that the Galaxy contains a lot of dark matter was the observation that the orbital velocities of stars did not decreases with increasing distance from the center of the Galaxy. Construct a rotation curve for the solar system by using the orbital velocities of the planets, which can be found in Appendix F. How does this curve differ from the rotation curve for the Galaxy? What does it tell you about where most of the mass in the solar system is concentrated?arrow_forwardConsider the following five kinds of objects: open cluster, giant molecular cloud, globular cluster, group of O and B stars, and planetary nebulae. A. Which occur only in spiral arms? B. Which occur only in the parts of the Galaxy other than the spiral arms? C. Which are thought to be very young? D. Which are thought to be very old? E. Which have the hottest stars?arrow_forwardAssume 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_forward
- Why didn’t astronomers before Shapley realize how large the galaxy is?arrow_forwardFrom the comments in the text about which kinds of stars produce emission nebulae and which kinds are associated with reflection nebulae, what can you say about the temperatures of the stars that produce NGC 1999 (Figure 20.13)? Figure 20.13 Pleiades Star Cluster. The bluish light surrounding the stars in this image is an example of a reflection nebula. Like fog around a street lamp, a reflection nebula shines only because the dust within it scatters light from a nearby bright source. The Pleiades cluster is currently passing through an interstellar cloud that contains dust grains, which scatter the light from the hot blue stars in the cluster. The Pleiades cluster is about 400 light-years from the Sun. (credit: NASA, ESA and AURA/Caltech)arrow_forwardThe luminosity of a Seyfert galaxy nucleus varies in a time-scale of 6 days. What could be the largest possible size of the emitting region?arrow_forward
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