UNDERSTANDING THE UNIVERSE(LL)-W/CODE
3rd Edition
ISBN: 9780393869903
Author: PALEN
Publisher: NORTON
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Chapter 14, Problem 31QAP
To determine
Reason behind the usage of X-ray, infrared and radio observations to probe the centre of our galaxy.
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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.
A given star orbits the center of its galaxy at an average speed of v_star, at a distance of r_star from the center. The galaxy has 2 spiral arms, and the arms themselves orbit slower than the star -- at the same radius, they orbit at a speed of v_arm (in the same direction as the star). The galaxy's age is t_gal. In the history of this galaxy, how many times did this star cross through a spiral arm?
Values: v_star = 200 km/s, r_star = 9 kpc, v_arms = 46 km/s, t_gal = 4 Gyr
Chapter 14 Solutions
UNDERSTANDING THE UNIVERSE(LL)-W/CODE
Ch. 14.1 - Prob. 14.1CYUCh. 14.2 - Prob. 14.2CYUCh. 14.3 - Prob. 14.3CYUCh. 14.4 - Prob. 14.4CYUCh. 14 - Prob. 1QAPCh. 14 - Prob. 2QAPCh. 14 - Prob. 3QAPCh. 14 - Prob. 4QAPCh. 14 - Prob. 5QAPCh. 14 - Prob. 6QAP
Ch. 14 - Prob. 7QAPCh. 14 - Prob. 8QAPCh. 14 - Prob. 9QAPCh. 14 - Prob. 10QAPCh. 14 - Prob. 11QAPCh. 14 - Prob. 12QAPCh. 14 - Prob. 13QAPCh. 14 - Prob. 14QAPCh. 14 - Prob. 15QAPCh. 14 - Prob. 16QAPCh. 14 - Prob. 17QAPCh. 14 - Prob. 18QAPCh. 14 - Prob. 19QAPCh. 14 - Prob. 20QAPCh. 14 - Prob. 21QAPCh. 14 - Prob. 22QAPCh. 14 - Prob. 23QAPCh. 14 - Prob. 24QAPCh. 14 - Prob. 25QAPCh. 14 - Prob. 27QAPCh. 14 - Prob. 28QAPCh. 14 - Prob. 29QAPCh. 14 - Prob. 30QAPCh. 14 - Prob. 31QAPCh. 14 - Prob. 32QAPCh. 14 - Prob. 33QAPCh. 14 - Prob. 34QAPCh. 14 - Prob. 35QAPCh. 14 - Prob. 36QAPCh. 14 - Prob. 37QAPCh. 14 - Prob. 38QAPCh. 14 - Prob. 39QAPCh. 14 - Prob. 40QAPCh. 14 - Prob. 41QAPCh. 14 - Prob. 43QAPCh. 14 - Prob. 44QAPCh. 14 - Prob. 45QAP
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- The Tully-Fischer method relies on being able to relate the mass of a galaxy to its rotation velocity. Stars in the outer-most regions of the Milky Way galaxy, located at a distance of 50 kpc from the galactic centre, are observed to orbit at a speed vrot = 250 km s−1. Using Kepler’s 3rd Law, determine the mass in the Milky Way that lies interior to 50 kpc. Express your answer in units of the Solar mass.arrow_forwardThe type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is [Select] and our Milky Way Galaxy is a [Select] barred spiral elliptical irregular F3 [Select] जी 4 4») Q Search DII de in % 5 spiral all of these galaxy types consist mostly of very old stars A 2 LO F7 & 7 PrtScn 8 Home P Endarrow_forwardThe 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? Explarrow_forward
- You observe the H-alpha line of Hydrogen in a distant galaxy to have a wavelength of 918.4 nm. What is the radial velocity of the galaxy?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_forwardAmong the globular clusters orbiting a distant galaxy, one is moving at 534 km/s and is located 14 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity, Vc = GM r ; make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 ✕ 1016 m.)arrow_forward
- You observe the H-beta line of Hydrogen in a distant galaxy to have a wavelength of 558.9 nm. What is the radial velocity of the galaxy?arrow_forwardOur galaxy is approximately 100,000 light years in diameter and 2,000 light years thick through the plane of the galaxy. If we were to compare the ratio of the diameter galaxy and its thickness to the ratio of the diameter of a CD and its thickness (CD has a diameter of 12 cm and thickness of 0.6 mm), what would be the factor differentiating those ratios? Put differently, if the galaxy were scaled down to the diameter of a CD, how many times thicker or thinner would the galaxy be than the CD? (For example if it would be twice as thick, you would answer 2 and if it were twice as thin you would answer 0.5 (aka 1/2))arrow_forwardSome interstellar Properties. Use excel calculator to fill in the missing figures. 1 ly = 365 × 24 × 60 × 60 × 300, 000km/s = 9.46 × 10^12 kmarrow_forward
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