Understanding Our Universe
3rd Edition
ISBN: 9780393614428
Author: PALEN, Stacy, Kay, Laura, Blumenthal, George (george Ray)
Publisher: W.w. Norton & Company,
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Chapter 17, Problem 43QAP
(a)
To determine
The number of galaxies present in figure.
(b)
To determine
The number of galaxies present in entire sky.
(c)
To determine
Use of cosmological principle to calculate galaxies.
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In the reading, you were told that there were roughly 10,000 galaxies in the image of the Hubble Ultra Deep Field alone. The image is roughly 10 square arcminutes and there are roughly 1.5*10^8 square arcminutes composing the entire sky. With that in mind and assuming that the Hubble Ultra Deep Field represents an average part of the sky, roughly how many galaxies may exist in the observable universe? (Please include commas for every factor of 1,000; for example 2,343,567,890)
Astronomers frequently say that "there are more stars in the universe than there are grains of sand on all the
beaches on the earth". Given that a typical grain of sand is about 0.5 – 1.0 mm in diameter, estimate the
number of grains of sand on all the earth's beaches. The diameter of the Earth is 12,742 km.
a) About 1011
b) About 1016
c) About 1021.
6.
Assume that a typical galaxy contains about 200 billion stars and that there are more than 150 billion
galaxies in the known universe. Estimate the total number of stars in the universe.
b) About 1022
a) About 1010
c) About 1016.
7.
Compare the values of the number of grains of sand in all earth's beaches (from problem 5) with the
number of stars in the universe (from problem 6) – which is greater?
a) Number of sand grains
b) number of stars
c) they are about the same.
=
2. Using a Hubble constant of Ho 70 km/s/Mpc, find the distance to the galaxy cluster that
moves with a velocity of 6500 km/s. Give your answer in megaparsecs and light-years.
Chapter 17 Solutions
Understanding Our Universe
Ch. 17.1 - Prob. 17.1CYUCh. 17.2 - Prob. 17.2CYUCh. 17.3 - Prob. 17.3CYUCh. 17.4 - Prob. 17.4CYUCh. 17.5 - Prob. 17.5CYUCh. 17 - Prob. 1QAPCh. 17 - Prob. 2QAPCh. 17 - Prob. 3QAPCh. 17 - Prob. 4QAPCh. 17 - Prob. 5QAP
Ch. 17 - Prob. 6QAPCh. 17 - Prob. 7QAPCh. 17 - Prob. 8QAPCh. 17 - Prob. 9QAPCh. 17 - Prob. 10QAPCh. 17 - Prob. 11QAPCh. 17 - Prob. 12QAPCh. 17 - Prob. 13QAPCh. 17 - Prob. 14QAPCh. 17 - Prob. 15QAPCh. 17 - Prob. 16QAPCh. 17 - Prob. 17QAPCh. 17 - Prob. 18QAPCh. 17 - Prob. 19QAPCh. 17 - Prob. 20QAPCh. 17 - Prob. 21QAPCh. 17 - Prob. 22QAPCh. 17 - Prob. 23QAPCh. 17 - Prob. 24QAPCh. 17 - Prob. 25QAPCh. 17 - Prob. 26QAPCh. 17 - Prob. 27QAPCh. 17 - Prob. 28QAPCh. 17 - Prob. 29QAPCh. 17 - Prob. 30QAPCh. 17 - Prob. 31QAPCh. 17 - Prob. 32QAPCh. 17 - Prob. 33QAPCh. 17 - Prob. 34QAPCh. 17 - Prob. 35QAPCh. 17 - Prob. 36QAPCh. 17 - Prob. 37QAPCh. 17 - Prob. 38QAPCh. 17 - Prob. 39QAPCh. 17 - Prob. 40QAPCh. 17 - Prob. 41QAPCh. 17 - Prob. 42QAPCh. 17 - Prob. 43QAPCh. 17 - Prob. 44QAPCh. 17 - Prob. 45QAP
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- If the diameter of the Milky Way Galaxys visible disk, 80,000 ly, is represented in a model by a dinner plate with a diameter of 10 inches, what is the model distance to galaxy M31, 2.6 millionly away? What is the model distance to the Virgo galaxy cluster, 16 Mpc away? (Convert answers to feet.)arrow_forwardBased on your analysis of galaxies in Table 26.1, is there a correlation between the population of stars and the quantity of gas or dust? Explain why this might be.arrow_forwardAssume that a typical galaxy contains about 200 billion stars and that there are more than 150 billion galaxies in the known universe. Estimate the total number of stars in the universe.arrow_forward
- Suppose that the outer stars of a galaxy have an orbital velocity of 150 km/s. If the radius of the galaxy is 4.0 kpc (1??? = 3.1 × 1016 ??), what is the orbital period of the outer stars in years?arrow_forwardgiven: a (distance to center of galaxy in AU) = 1,717,914,439 AU P (suns orbital period in years) = 203,782,828.3 years M (mass of milky way galaxy in solar masses) = 1.22 x 10^11 Msun Question: Assume the Milky Way Galaxy is made up entirely of stars like the Sun, i.e. on average each star has the mass of 1 MSun. Under this assumption, approximately how many stars are there in our galaxy? Express this answer in billions of stars (1 billion = 109).arrow_forwardHow astronomers determine the distance of a galaxy? Explain.arrow_forward
- For a circular velocity profile of the type (r) = ar¹ ar1/9, where a is a constant and r is the radial distance from the centre of a spiral galaxy, find the ratio (r)/(r), where (r) is the epicyclic frequency and 2(r) is the angular velocity. Enter your answer to 2 decimal places.arrow_forwardThe Kormendy relation for ellipticals can be written as He = 20.2+ 3.0 log R. where R. is the half-light radius (in kpc) and 4e is the surface brightness (in magnitudes per square arc second) at R.. An elliptical galaxy obeying this relation will have a total luminosity Lo R for some index 7. What is the correct value of n? O a. n=-6/5 O b. n= 4/5 T23D Oc n= 16/5 O d. n cannot be determined with the information we have.arrow_forwardGiven the ideas presented here about how galaxies form, would you expect to find a giant elliptical galaxy in the Local Group? Why or why not? Is there in fact a giant elliptical in the Local Group?arrow_forward
- Assume that the average galaxy contains 1011MSunand that the average distance between galaxies is 10 million light-years. Calculate the average density of matter (mass per unit volume) in galaxies. What fraction is this of the critical density we calculated in the chapter?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_forwardMost distances in the Galaxy are measured in light-years instead of meters. Why do you think this is the case?arrow_forward
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