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Foundations of Astronomy

Michael A. Seeds

Chapter 16

Galaxies - all with Video Answers

Educators

Chapter Questions

01:14

Problem 1

If a galaxy contains a type I (classical) Cepheid with a period of 30 days and an apparent magnitude of $20,$ what is the distance to the galaxy?

Farhanul Hasan
Farhanul Hasan
Numerade Educator
01:34

Problem 2

If you find a galaxy that contains globular clusters that are 2 seconds of arc in diameter, how far away is the galaxy? (Hints: Assume that a globular cluster is 25 pc in diameter and use the small-angle formula.)

Prashant Bana
Prashant Bana
Numerade Educator
00:43

Problem 3

If a galaxy contains a supernova that at its brightest has an apparent magnitude of $17,$ how far away is the galaxy? (Hint: Assume that the absolute magnitude of the supernova is $-19 .$

Sarah Mccrumb
Sarah Mccrumb
Numerade Educator
01:47

Problem 4

If you find a galaxy that is the same size and mass as our Milky Way Galaxy, what orbital velocity would a small satellite galaxy have if it orbited 50 kpc from the center of the larger galaxy?

Sheh Lit Chang
Sheh Lit Chang
University of Washington
03:43

Problem 5

Find the orbital period of the satellite galaxy described in Problem 4

Andy Chen
Andy Chen
Numerade Educator
02:11

Problem 6

If a galaxy has an apparent radial velocity of $2000 \mathrm{km} / \mathrm{s}$ and the Hubble constant is $70 \mathrm{km} / \mathrm{s} / \mathrm{Mpc}$, how far away is the galaxy? (Hint:
Use the Hubble law.)

Matthew Miranda
Matthew Miranda
Numerade Educator
02:18

Problem 7

If you find a galaxy that is 20 minutes of arc in diameter and you measure its distance to be $1 \mathrm{Mpc}$, what is its diameter?

Guilherme Barros
Guilherme Barros
Numerade Educator
02:48

Problem 8

Suppose you found a galaxy in which the outer stars have orbital velocities of $150 \mathrm{km} / \mathrm{s}$. If the radius of the galaxy is $4 \mathrm{kpc}$, what is the orbital period of the outer stars? (Hints: 1 pc $=3.08 \times 10^{13} \mathrm{km},$ and $1 \mathrm{yr}=3.15 \times 10^{7}$ seconds.

Harper Auman
Harper Auman
Numerade Educator
03:23

Problem 9

A galaxy has been found that is $5 \mathrm{kpc}$ in radius and whose outer stars orbit the center with a period of 200 million years. What is the mass of the galaxy? 0 n what assumptions does this result depend?

Mayukh Banik
Mayukh Banik
Numerade Educator
01:20

Problem 10

Among the globular clusters orbiting a distant galaxy, the fastest is traveling $420 \mathrm{km} / \mathrm{s}$ and is located $11 \mathrm{kpc}$ from the center of the galaxy. Assuming the globular cluster is just barely gravitationally bound to the galaxy, what is the mass of the galaxy? (Hint: The galaxy had a slightly faster globular cluster, but it escaped some time ago. What is the escape velocity?)

Prabhu Ramji
Prabhu Ramji
Numerade Educator