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 19, Problem 31Q
To determine
The reason for Cepheid stars pulsation.
The reason for Cepheid stars to be important to astronomers.
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The figure below shows the spectra of two galaxies A and B.
A galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance
from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen-
tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe
dark matter exists. Let's work out why!
Assuming that each star in a given galaxy has a circular orbit, we know that the accelera-
tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and
equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected
relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat
rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro-
tation curve and must therefore be the general profile that dark matter follows in our galaxy.
The figure below shows the spectra of two galaxies A and B.
Please can i get help with this questions below:
1. Which of these galaxies has ongoing star formation? How can you tell?2. One of these galaxies has Hubble type E3 while the other is SBb. Which is which? What does the 3 inE3 tell you about the galaxy? What does the SB in SBb tell you about the galaxy?3. What effects would dust have on the two spectra?4. Which galaxy would you expect to have more far-infrared emission? Expl
Chapter 19 Solutions
Universe: Stars And Galaxies
Ch. 19 - Prob. 1QCh. 19 - Prob. 2QCh. 19 - Prob. 3QCh. 19 - Prob. 4QCh. 19 - Prob. 5QCh. 19 - Prob. 6QCh. 19 - Prob. 7QCh. 19 - Prob. 8QCh. 19 - Prob. 9QCh. 19 - Prob. 10Q
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- Consider 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_forwardThe best parallaxes obtained with Hipparcos have an accuracy of 0.001 arcsec. If you want to measure the distance to a star with an accuracy of 10%, its parallax must be 10 times larger than the typical error. How far away can you obtain a distance that is accurate to 10% with Hipparcos data? The disk of our Galaxy is 100,000 light-years in diameter. What fraction of the diameter of the Galaxy’s disk is the distance for which we can measure accurate parallaxes?arrow_forwardLooking for ___ pcarrow_forward
- Globular clusters contain no stars more massive than the Sun. Which of the following seems like the least reasonable implication of this observation? Group of answer choices Globular clusters are very old. Globular clusters are very young. Only the low-mass stars are still "alive" in the clusters. Many red giants can probably be found in globular clusters. The very massive stars in the globular clusters have already burnt out.arrow_forwardIf the RR Lyrae stars in a globular cluster have average apparent magnitudes of +19, how far away (in pc) is the cluster? (Hints: See the following figure, and use the magnitude-distance formula: d = 10(mv - My+5)/5.) Туре (Classical) Cepheids 104 103 Туре II Cepheids 102 RR Lyrae stars 0.3 1 10 30 100 Pulsation perlod (days) pc Absolute magnitude Luminosity, L L.arrow_forwardIf the hottest star in the Carina Nebula has a surface temperature of 51,000 K, at what wavelength (in nm) does it radiate the most energy? Hint: Use Wien's law: ?max = 2.90 ✕ 106 nm · K T How does that compare with 91.2 nm, the wavelength of photons with just enough energy to ionize hydrogen? -The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen. -The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen. -The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen. -The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.arrow_forward
- Globular clusters revolve around the Galaxy in highly elliptical orbits. Where would you expect the clusters to spend most of their time? (Think of Kepler’s laws.) At any given time, would you expect most globular clusters to be moving at high or low speeds with respect to the center of the Galaxy? Why? (If you would like to learn more about globular clusters, read Section 22.2 of the book, though it is not necessary to answer this question)arrow_forwardLet’s say you’re looking for extrasolar planets. You observe a star that has a spectral shift in the line that is supposed to be at at 656.28011 nm – this star shows this line at 656.28005 nm. What is the radial velocity of star (in m/s) and in what direction in relation to you? a) 27.4 m/s, towards b) 27.4 km/s, away c) -27.4 m/s, toward d) -27.4 km/s, awayarrow_forwardCan you please help with Part 2 of 2? Thank you.arrow_forward
- Hotter, more massive stars are virtually absent from globular clusters. What does this tell us? a) Only that for some reason, massive stars never formed in these clusters. b) Globular clusters are among the youngest objects in our galaxy. c) Globular clusters are among the oldest objects in the Galaxy.arrow_forwardWhere in the Galaxy would you expect to find Type II supernovae, which are the explosions of massive stars that go through their lives very quickly? Where would you expect to find Type I supernovae, which involve the explosions of white dwarfs?arrow_forwardAre the galaxies red-shifting or blue-shifting? Explain. (You may find the big-bang theory helpful). Andromeda galaxy is currently approaching our galaxy with a radial velocity of 266 km/sec. How far is our galaxy from Andromeda? (Hubble’s constant, H, is 73 km/sec/MParsec). When can the two galaxies be anticipated to collide?arrow_forward
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