College Physics
OER 2016 Edition
ISBN: 9781947172173
Author: OpenStax
Publisher: OpenStax College
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Chapter 34, Problem 27PE
If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be? Assume the average mass of a MACHO is 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Way galaxy with its 1011 stars of average mass 1.5 times the Sun’s mass.
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If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be?Assume the average mass of a MACHO is 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Way galaxy with its 1011 stars of average mass 1.5 times the Sun’s mass.
Suppose that stars were born at random times over the last 1010 years. The rate of star formation is simply the number of stars divided by 1010 years. The fraction of stars with detected extrasolar planets is at least 10 %. The rate of star formation can be multiplied by this fraction to find the rate planet formation. How often (in years) does a planetary system form in our galaxy? Assume the Milky Way contains 9 × 1011 stars.
If the dark matter in the Milky Way were composed entirely of MACHOs (evidence shows it is not), approximately how many would there have to be? Assume the average mass of a MACHO is 1/1000 that of the Sun, and that dark matter has a mass 10 times that of the luminous Milky Waygalaxy with its 1011 stars of average mass 1.5 times the Sun’s mass.
Chapter 34 Solutions
College Physics
Ch. 34 - Explain why it only appears that we are at the...Ch. 34 - If there is no observable edge to the universe,...Ch. 34 - If the universe is infinite, does it have a...Ch. 34 - Another known cause of red shift in light is the...Ch. 34 - If some unknown cause of red shiftsuch as light...Ch. 34 - Olbers’s paradox poses an interesting question: If...Ch. 34 - If the cosmic microwave background radiation...Ch. 34 - The decay of one type of Kmeson is cited as...Ch. 34 - Distances to local galaxies are determined by...Ch. 34 - Distances to very remote galaxies are estimated...
Ch. 34 - If the smallest meaningful time interval is...Ch. 34 - Quantum gravity, if developed, would be an...Ch. 34 - Does observed gravitational lensing correspond to...Ch. 34 - Suppose you measure the red shifts of all the...Ch. 34 - What are gravitational waves, and have they yet...Ch. 34 - Is the event horizon of a black hole the actual...Ch. 34 - Suppose black holes radiate their mass away and...Ch. 34 - Discuss the possibility that star velocities at...Ch. 34 - How does relativistic time dilation prohibit...Ch. 34 - If neutrino oscillations do occur, will they...Ch. 34 - Lacking direct evidence of WIMPs as dark matter,...Ch. 34 - Must a complex system be adaptive to be of...Ch. 34 - State a necessary condition for a System to be...Ch. 34 - What is critical temperature Tc? Do all materials...Ch. 34 - Explain how good thermal contact with liquid...Ch. 34 - Not only is liquid nitrogen a cheaper coolant than...Ch. 34 - For experimental evidence particularly of...Ch. 34 - Discuss whether you think there are limits to what...Ch. 34 - Find the approximate mass of the luminous matter...Ch. 34 - Find the approximate mass of the dark and luminous...Ch. 34 - (a) Estimate the mass of the luminous matter in...Ch. 34 - If a galaxy is 500 Mly away from us, how fast do...Ch. 34 - On average, how far away are galaxies mat are...Ch. 34 - Our solar system orbits the center of the Milky...Ch. 34 - (a) What is the approximate speed relative to us...Ch. 34 - (a) Calculate The approximate age of the universe...Ch. 34 - Assuming a circular orbit for the Sun about the...Ch. 34 - (a) What is the approximate force of gravity on a...Ch. 34 - Andromeda galaxy is the closest large galaxy and...Ch. 34 - (a) A particle and its antiparticle are at rest...Ch. 34 - The average particle energy needed to observe...Ch. 34 - The peak intensity of the CMBR occurs at a...Ch. 34 - (a) What Hubble constant corresponds to an...Ch. 34 - Show that the velocity of a star orbiting its...Ch. 34 - The core of a star collapses during a supernova,...Ch. 34 - Using data from the previous problem, find the...Ch. 34 - Distances to the nearest stars (up to 500 by away)...Ch. 34 - (a) Use the Heisenberg uncertainty principle to...Ch. 34 - Construct Your Own Problem Consider a star moving...Ch. 34 - What is the Schwarzschild radius of a blank hole...Ch. 34 - Black holes with masses smaller than muse formed...Ch. 34 - Supermassive black holes are thought to exist at...Ch. 34 - Construct Your Own Problem Consider a supermassive...Ch. 34 - The characteristic length of entities in...Ch. 34 - If the dark matter in the Milky Way were composed...Ch. 34 - The critical mass density needed to just halt the...Ch. 34 - Assume the average density of the universe is 0.1...Ch. 34 - To get an idea of how empty deep spam is on the...Ch. 34 - A section of superconducting wire carries a...
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- Let's say that the number density of galaxies in the universe is, on average, 3 × 10–68 galaxies/m3. If astronomers could observe all galaxies out to a distance of 1010 light-years, how many galaxies would they find? (Note that there are 1016 meters in 1 light-year.)arrow_forwardmathematician Archimedes, responding to a claim that the number of grains of sand was infinite, calculated that the number of grains of sand needed to fill the universe was on the order of 1063. Our understanding of the size of the universe has changed since then, and we now know that the observable universe alone is a sphere with a radius of 1026 m. Estimating the size of a grain of sand, A) Approximately how many grains of sand would fill the observable universe? B) How many times larger or smaller is this number than Archimedes' result?arrow_forwardUsing our example from the previous unit, let's try to determine the Hubble time for this example universe. You were given that a good representative galaxy receded at a speed of 4000 km/s and was found to be 20 Mpc away. With that in mind, what would the age of that universe be in years (aka what is that universe's Hubble time)? Go ahead and take the number of kilometers per Mpc to be approximately 3.1*10^19 km/Mpc. While this problem may look scary at first, this is really just bringing you full circle to one of the unit conversion problems you encountered at the beginning of this course.arrow_forward
- 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_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_forwardIn 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)arrow_forward
- Stars form in the Milky Way at a rate of about 1 solar mass per year. At this rate, how long would it take for all the interstellar gas in the Milky Way to be turned into stars if there were no fresh gas coming in from outside? How does this compare to the estimated age of the universe, 14 billion years? What do you conclude from this?arrow_forwardWhat evidence can you give that we live in a galaxy?arrow_forwardAssume 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_forward
- 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_forwardSuppose the average mass of a star in the Galaxy is one-third of a solar mass. Use the value for the mass of the Galaxy that we calculated in Exercise 25.19, and estimate how many stars are in the Milky Way. Give some reasons it is reasonable to assume that the mass of an average star is less than the mass of the Sun.arrow_forwardThe best evidence for a black hole at the center of the Galaxy also comes from the application of Kepler’s third law. Suppose a star at a distance of 20 light-hours from the center of the Galaxy has an orbital speed of 6200 km/s. How much mass must be located inside its orbit?arrow_forward
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