Chapter 75, Types of Galaxies Video Solutions, Pathways to Astronomy

Problem 1

For each of the following distances, if a galaxy the size of the Milky Way (about $30 \mathrm{kpc}$ in diameter) were at that distance from the Milky Way, what would its angular size (Unit 10.4 ) appear to be? Express your answers in arc minutes.
a. $10 \mathrm{Mpc}$
b. $1000 \mathrm{Mpc}$

Zachary Warner

Numerade Educator

01:46

Problem 2

If the typical distance between galaxies is 1 million $\mathrm{pc}(1 \mathrm{Mpc})$ how many galaxies are found in a sphere of radius 1 million $\mathrm{Mpc} ?$

Farhanul Hasan

Numerade Educator

01:56

Problem 3

For the majority of galaxies astronomers observe, the light travel time is less than a billion years. This is only a fraction of the Sun's age, and therefore we do not expect to find many differences in the galaxies' properties due to their age. What would the redshift be for a galaxy that we are seeing as it was billion years ago?

Farhanul Hasan

Numerade Educator

00:37

Problem 4

The Hubble Deep Field covers an area of about 5 arcmin $^{2}$ and contains about 3000 galaxies. If we observed the entire sky to this depth, about how many galaxies would we find?

Sarah Mccrumb

Numerade Educator

04:01

Problem 5

The radial velocity of M31 toward the Milky Way is about $100 \mathrm{km} / \mathrm{sec} .$ If it maintains that speed, how long will it take to travel the 700 -kpc distance between the two galaxies?

Guilherme Barros

Numerade Educator

02:13

Problem 6

Assume that the disk of the Milky Way has a diameter of $40 \mathrm{kpc}$ and has a surface area $R^{2}$. Likewise, each star covers an area determined by $R^{2}.$
a. If the Milky Way contains 100 billion stars each the size of the Sun, what fraction of the galaxy's disk is actually "covered" by a star?
b. The fraction found in (a) expresses the approximate chance that when a single star passes through the Milky Way's disk, it will strike a star. If another galaxy with the same number of stars passed through the Milky Way, how many stars would you estimate would undergo direct collisions?

Narayan Hari

Numerade Educator