Principles of Physics: A Calculus-Based Text
5th Edition
ISBN: 9781133104261
Author: Raymond A. Serway, John W. Jewett
Publisher: Cengage Learning
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Chapter 31, Problem 2OQ
To determine
The comparison between average density of the solar system with the critical density required for the Universe to stop its Hubble’s law expansion.
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Recent findings in astrophysics suggest that the observable universe can be modeled as a sphere of radius R=13.7x109 light-years=13.0 x 1025m with an average total mass density of about 1x10-26 kg/m3 Only about 4% of total mass is due to “ordinary” matter (such as protons, neutrons, and electrons). Estimate how much ordinary matter (in kg) there is in the observable universe. (For the light-year, see Problem 19.)
I asked the following question and was given the attached solution:
Suppose that the universe were full of spherical objects, each of mass m and radius r . If the objects were distributed uniformly throughout the universe, what number density (#/m3) of spherical objects would be required to make the density equal to the critical density of our Universe?
Values:
m = 4 kg
r = 0.0407 m
Answer must be in scientific notation and include zero decimal places (1 sig fig --- e.g., 1234 should be written as 1*10^3)
I don't follow the work and I got the wrong answer, so please help and show your work as I do not follow along easily
thanks
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.
Chapter 31 Solutions
Principles of Physics: A Calculus-Based Text
Ch. 31.2 - Given the identification of the particles in...Ch. 31.5 - Prob. 31.2QQCh. 31.5 - Prob. 31.3QQCh. 31.5 - Prob. 31.4QQCh. 31.9 - Prob. 31.5QQCh. 31 - Prob. 1OQCh. 31 - Prob. 2OQCh. 31 - Prob. 3OQCh. 31 - Prob. 4OQCh. 31 - Prob. 5OQ
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- You observe a star orbiting in the outer parts of a galaxy. The distance to this galaxy is known, and you are able to take a spectra of this star and determine its velocity. The star is 19 kpc from the galaxy center and moving in a circular orbit with speed 369 km/s. Compute the total mass of the galaxy internal to the star's orbit. You will get a large number; express it in scientific notation and in units of solar masses [e.g., 4.2e10]. [Hint: there is a Box in Chapter 22 of your textbook that will be of help. See also the course formula sheet.]arrow_forwardThe visible section of the Universe is a sphere centered on the bridge of your nose, with radius 13.7 billion light-years. (a) Explain why the visible Universe is getting larger, with its radius increasing by one light-year in every year. (b) Find the rate at which the volume of the visible section of the Universe is increasing.arrow_forwardPretend that galaxies are spaced evenly, 7.0 Mpc apart, and the average mass of a galaxy is 1.0 ✕ 1011 M. What is the average density (in kg/m3) of matter in the universe? (Note: The volume of a sphere is 4/3pieR^3 and the mass of the sun is 2.0 ✕ 1030 kg.) ______ kg/m^3 Which model universe does this density value support? A: open B: flat C: closedarrow_forward
- The nearest neutron star (a collated star made primarily of neutrons) is about 3.00 1018 m away from Earth. Given that the Milky Way galaxy (Fig. P1.81) is roughly a disk of diameter 1021 m and thickness 1019 m, estimate the number of neutron stars in the Milky Way to the nearest order of magnitude. Figure P1.81arrow_forwardA star is 1.0 x 104 ly (light-years) from the center of its galaxy and is moving in a circle around that center at a speed of 110 km/s. (a) How long does it take the star to make one revolution about the galactic center? (b) How many revolutions has the star completed since it was formed about 5.6 x 109 years ago?arrow_forwardSuppose we find an Earth-like planet around one of our nearest stellar neighbors, Alpha Centauri (located only 4.4 light-years away). If we launched a "generation ship" at a constant speed of 1500.00 km/s from Earth with a group of people whose descendants will explore and colonize this planet, how many years before the generation ship reached Alpha Centauri? (Note there are 9.46 ××1012 km in a light-year and 31.6 million seconds in a year.arrow_forward
- The sun orbits the center of the Milky Way galaxy for a period of 2.5x10^8 years. (a) Assuming a circular orbit of radius 2.4x10^20 m, compute the mass of the Milky Way. (b) Estimate the number of stars in the Milky Way, assuming the average star mass equals the mass of the sun—2.0x10^30 kgarrow_forwardObservations indicate that each galaxy contains a supermassive black hole at its center. These black holes can be hundreds of thousands to billions of times more massive than the Sun. Astronomers estimate the size of such black holes using multiple methods. One method, using the orbits of stars around the black hole, is an application of Kepler's third law. The mass of the black hole can be found by using the given equation, where a is the semi-major axis in astronomical units, P is the period in years, and k is a constant with a value of 1 Mo X year²/ AU³. a³ M = k- p² What is the mass of a supermassive black hole if a star orbits it with a semimajor axis of 959 AU and a period of 13.3 years? mass: Another method measures the speed of gas moving past the black hole. In the given equation, v is the velocity of the gas (in kilometers per second), r is the distance of the gas cloud from the black hole (in kilometers), and G is Newton's gravitational constant. In this equation, G = 1.33 ×…arrow_forwardn(r) = 1ge where r represents the distance from the centre of the Galaxy, Ro is the distance of the Sun from the centre of the Galaxy, Ra is the typical size of disk and no is the stellar density of disk at the position of the Sun. All distances are expressed in kpc. An astronomer observes the center of the Galaxy within a small field of view. We take a particular type of Red giant stars as the standard candles for the observation with approximately constant absolute magnitude of M = -0.2, (a) A telescope has a limiting magnitude of m = 18. Calculate the maximum distance to which this telescope can detect these red giant stars. For simplicity we ignore the presence of interstellar medium so there is no extinction. (b) Assume an extinction of 0.7 mag/kpc for the interstellar medium. Repeat the calculation as done in the part 5a and obtain a rough number for the maximum distance these red giant stars can be observed. (c) Give an expression for the number of these red giant stars per mag-…arrow_forward
- What would be your estimate for the age of the universe if you measured Hubbleʹs constant to be 33 km/s/Mly? You can assume that the expansion rate has remained unchanged during the history of the universe.arrow_forwardProblem 6. The average density p of the Universe today is 3 x 10-27kgm-³. -3 1. Find this density in (a) gcm-³ (b) M.Mpc-³ (c) m₂cm-³ 2. Find the mass within a sphere of radius (a) R. (b) 1 AU (c) 10 Mpcarrow_forwardIf our Sun (mass = 1.99××103030 kg, radius = 6.96××1088 m) were to collapse into a neutron star (an object composed of tightly packed neutrons with roughly the same density as neutrons within a nucleus, ρnucleusρnucleus = 2.3××101717 kg/m33), what would the new radius of our “neutron-sun” be?arrow_forward
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