21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Chapter 20, Problem 28QP
To determine
The origin of the Milky Way’s satellite galaxies, the fate of most of the Milky Way’s satellite galaxies and the Milky Way’s satellite galaxies so difficult to detect.
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Chapter 20 Solutions
21st Century Astronomy
Ch. 20.1 - Prob. 20.1CYUCh. 20.2 - Prob. 20.2CYUCh. 20.3 - Prob. 20.3CYUCh. 20.4 - Prob. 20.4CYUCh. 20 - Prob. 1QPCh. 20 - Prob. 2QPCh. 20 - Prob. 3QPCh. 20 - Prob. 4QPCh. 20 - Prob. 5QPCh. 20 - Prob. 6QP
Ch. 20 - Prob. 7QPCh. 20 - Prob. 8QPCh. 20 - Prob. 9QPCh. 20 - Prob. 10QPCh. 20 - Prob. 11QPCh. 20 - Prob. 12QPCh. 20 - Prob. 13QPCh. 20 - Prob. 14QPCh. 20 - Prob. 15QPCh. 20 - Prob. 16QPCh. 20 - Prob. 17QPCh. 20 - Prob. 18QPCh. 20 - Prob. 19QPCh. 20 - Prob. 20QPCh. 20 - Prob. 21QPCh. 20 - Prob. 22QPCh. 20 - Prob. 23QPCh. 20 - Prob. 24QPCh. 20 - Prob. 25QPCh. 20 - Prob. 26QPCh. 20 - Prob. 27QPCh. 20 - Prob. 28QPCh. 20 - Prob. 29QPCh. 20 - Prob. 30QPCh. 20 - Prob. 31QPCh. 20 - Prob. 32QPCh. 20 - Prob. 33QPCh. 20 - Prob. 34QPCh. 20 - Prob. 35QPCh. 20 - Prob. 36QPCh. 20 - Prob. 37QPCh. 20 - Prob. 38QPCh. 20 - Prob. 39QPCh. 20 - Prob. 40QPCh. 20 - Prob. 41QPCh. 20 - Prob. 42QPCh. 20 - Prob. 43QPCh. 20 - Prob. 44QPCh. 20 - Prob. 45QP
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- Suppose three stars lie in the disk of the Galaxy at distances of 20,000 light-years, 25,000 light-years, and 30,000 light-years from the galactic center, and suppose that right now all three are lined up in such a way that it is possible to draw a straight line through them and on to the center of the Galaxy. How will the relative positions of these three stars change with time? Assume that their orbits are all circular and lie in the plane of the disk.arrow_forwardChoose the statement that is NOT true of a galaxy. O Galaxies take different shapes depending on how the stars are distributed and oriented. O Agreat island of stars held together by gravity. All galaxies are basically of the same shape and consist mainly of a discs and a halos. All the stars in a galary orbit a common centerarrow_forwardAre the galaxies red-shifting or blue-shifting? Explain. (You may find the big-bang theory helpful). Andromeda galaxy is currently approaching our galaxy with a radial velocity of 266 km/sec. How far is our galaxy from Andromeda? (Hubble’s constant, H, is 73 km/sec/MParsec). When can the two galaxies be anticipated to collide?arrow_forward
- Which of the following statements best describes our galaxy, the Milky Way? O A bulge dominated system, with little or no disk, approximately 27,000 light years across. A disk 100,000 lightyears across filled with gas and stars, with a bulge of older stars in the galaxy centre. A disk 27,000 light years across with a bulge of gas and newly formed stars in the galaxy centre. O A spherical (elliptical) galaxy, 100,000 lightyears across, with no gas and no new stars.arrow_forwardHow astronomers determine the distance of a galaxy? Explain.arrow_forwardA 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 Gyrarrow_forward
- 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.arrow_forwardSuppose you have obtained spectra of several galaxies and have measured the observed wavelength of the H-Alpha line (rest wavelength = 656.3 nm) to be Galaxy 1: 658.1 nm. Galaxy 2: 667.1 nm. Galaxy 3: 677.6 nm. Calculate the radial velocity of each of these galaxies.arrow_forwardIf you will compare the balloon to our universe, with the dots / markings as galaxies or galaxy clusters, what can you say about the distances of the galaxies as continuously expands?arrow_forward
- 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.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_forwardWhich of the following best describe the reasons we have to infer that a supermassive blackhole lurks in the centre of our galaxy? Stars keep disappearing from view as they get swallowed up in the galactic centre. Tight orbit of stars around an invisible companion & giant bubbles of cold, star forming gas have been expelled from galactic centre. We can measure the gravitational waves coming from such an enormous black hole. O Tight orbit of stars around an invisible companion & giant bubbles filled with gamma rays expelled from the galactic centre.arrow_forward
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