FOUNDATIONS OF ASTRONOMY (LL)-W/MINDTAP
14th Edition
ISBN: 9780357000502
Author: Seeds
Publisher: CENGAGE L
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Chapter 15, Problem 21RQ
To determine
Whether the black hole at the nucleus of Milky Way Galaxy is a remnant of single star or not.
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The Sun is moving at 220 ??/? around the Galactic Center at a more-or-less constant distance of 8.5 ???. To appreciate how remarkable this is, consider the following questions:
a) How massive would the Sun have to be for the Earth to have an orbital velocity of 220 km/s at 1 AU?
b) How fast would the Earth move if it was in orbit around the Sun at a distance of 8.5 kpc? Of course, you may ignore the effects of all other stars in this calculation.
Assume that the number density of stars in the Milky Way is 0.14 pc-3.
(e)
There are 10" stars uniformly distributed across the galaxy. Also assume that
there is one supernova every 30 years and all of them have same luminosity.
Find the probablity, P, of a supernova causing extinction on Earth in total life
span of the Sun.
It is possible to derive the age of the universe given the value of the Hubble constant and the distance to a galaxy, again with the assumption that the value of the Hubble constant has not changed since the Big Bang. Consider a galaxy at a distance of 235 million light-years receding from us at a velocity, v. If the Hubble constant is 20.5 km/s per million light-years, what is its velocity? (Enter the magnitude in km/s.)
_________ km/s
Chapter 15 Solutions
FOUNDATIONS OF ASTRONOMY (LL)-W/MINDTAP
Ch. 15 - What evidence can you give that we live in a...Ch. 15 - Prob. 2RQCh. 15 - Why didnt astronomers before Shapley realize how...Ch. 15 - Prob. 4RQCh. 15 - Prob. 5RQCh. 15 - Prob. 6RQCh. 15 - Which parts of a spiral galaxy comprise the...Ch. 15 - Prob. 8RQCh. 15 - Prob. 9RQCh. 15 - Prob. 10RQ
Ch. 15 - Prob. 11RQCh. 15 - Prob. 12RQCh. 15 - Prob. 13RQCh. 15 - Prob. 14RQCh. 15 - Prob. 15RQCh. 15 - Prob. 16RQCh. 15 - Prob. 17RQCh. 15 - Prob. 18RQCh. 15 - Prob. 19RQCh. 15 - Prob. 20RQCh. 15 - Prob. 21RQCh. 15 - Prob. 22RQCh. 15 - Prob. 23RQCh. 15 - Prob. 24RQCh. 15 - Prob. 25RQCh. 15 - Prob. 26RQCh. 15 - Rank these objects from oldest to youngest the...Ch. 15 - What evidence contradicts the top-down hypothesis...Ch. 15 - Prob. 29RQCh. 15 - The story of a process makes the facts easier to...Ch. 15 - Prob. 1PCh. 15 - Prob. 2PCh. 15 - Prob. 3PCh. 15 - Prob. 4PCh. 15 - Prob. 5PCh. 15 - Prob. 6PCh. 15 - Prob. 7PCh. 15 - Prob. 8PCh. 15 - If the Sun is 4.6 billion years old, how many...Ch. 15 - Prob. 10PCh. 15 - Prob. 11PCh. 15 - Prob. 12PCh. 15 - Prob. 13PCh. 15 - Prob. 14PCh. 15 - Prob. 15PCh. 15 - Prob. 1SOPCh. 15 - Prob. 2SOPCh. 15 - Prob. 2LTLCh. 15 - Prob. 3LTLCh. 15 - Prob. 4LTLCh. 15 - Prob. 5LTL
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- 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 18%. 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 8 × 1011 stars.arrow_forwardConsider the Milky Way disk, which has a 50 kpc diameter and a total height of 600 pc. Suppose that the Sun orbits precisely at the mid-plane of the disk in a circular orbit. Supernovae explosions happen randomly throughout the disk at a rate of about 2 per 100 years. Consider a spherical region around the Sun with a radius of 300 pc. Ignore the Milky Way bulge and halo in this problem; assume the Milky Way disk is perfectly uniform and extends all the way through the region of the bulge. (I.e., the Milky Way is modeled *only* as a cylindrical disk--like a hockey puck-- with constant density throughout.) If a particular supernova goes off at a random location within the disk, what is the probability that it went off in the 300 pc radius spherical region near the Sun? Express your probability as a percentage (but without writing the percent sign). [Hint: there is a 100% probability that the supernova went off somewhere in the volume of the Milky Way disk; there is a 50% probability that…arrow_forwardThe 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_forward
- What is the orbital period of a bit of matter in an accretion disk that is located 8 x 10^5 km from a 82 M black hole? (Hint: Use the circular orbit velocity formula, V c = GM/R)arrow_forwardWould a human have been possible during the first generation of stars that formed right after the Big Bang? Why or why not?arrow_forwardWhat is the evidence that star formation began when the universe was only a few hundred million years old?arrow_forward
- Would you expect to observe every supernova in our own Galaxy? Why or why not?arrow_forwardA Type la supernova explodes in a galaxy at a distance of 6.10×107 light-years from Earth. If astronomers detect the light from the supernova today, how many years T have passed since the supernova exploded? T= 2.07 x10 -5 years Given a Hubble constant of 74.3 km/s/Mpc, at what speed v is this galaxy moving away from Earth? v= km/s What is this galaxy's redshift? redshift:arrow_forwardWhat has happened to the CMBR since the Big Bang?arrow_forward
- Use the Schwarzchild formula, Rs = 2GM/c2 , where Rs = Radius of the star, in meters, that would cause it to become a black hole M = Mass of the star, in kilograms, G = A constant, called the gravitational constant = 6.7 * 10-11m3/kg .s2, c = Speed of light = 3 * 108 meters per second. to determine to what length the radius of the Sun must be reduced for it to become a black hole. The Sun’s mass is approximately 2 * 1030 kilograms ?arrow_forwardA 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.arrow_forwardSuppose that stars were born at random times over the last 10e10 years. The rate ofstar formation is simply the number of stars divided by 10e10 years. The fraction ofstars with detected extrasolar planets is at least 9 %. The rate of star formation can bemultiplied by this fraction to find the rate planet formation. How often (in years) doesa planetary system form in our galaxy? Assume the Milky Way contains 7 × 10e11 stars. I've done this problem 3 different times from scratch and looked at similar problems here. Each time my answer is 1.587 (1.59 rounded to 2 significant figures), but when I submit, it says the answer is wrong. What do you think?arrow_forward
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