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Pathways to Astronomy

Stephen E. Schneider

Chapter 76

Galaxy Clustering - all with Video Answers

Educators

Chapter Questions

01:11

Problem 1

Some galaxies in the Virgo Cluster are found to be moving at $1000 \mathrm{km} / \mathrm{sec}$ through the center of the cluster. How long would it take to move 1 Mpc at that speed?

Zachary Warner
Zachary Warner
Numerade Educator
02:20

Problem 2

The Great Attractor, located some 50 Mpc away, is suspected to have caused the Local Group to accelerate to a speed of
$500 \mathrm{km} / \mathrm{sec}$ over the last 13 billion years.
a. What is the average acceleration over that time, expressed in $\mathrm{m} / \mathrm{sec}^{2} ?$
b. Using Newton's law of gravitation, how big a mass would be needed at that distance to produce the observed acceleration?

Mayukh Banik
Mayukh Banik
Numerade Educator
03:19

Problem 3

The spectral line of hydrogen producing the quasar absorption lines in most studies has a laboratory wavelength of $122 \mathrm{nm}$. If
a hydrogen cloud is at a distance of 1 billion ly,
a. use Hubble's law to find the recession velocity of this cloud.
b. what is the redshift of the cloud?
c. at what wavelength will the absorption occur?

Jack Gage
Jack Gage
Numerade Educator
01:56

Problem 4

Suppose that the typical galaxy has a mass of $10^{11} \mathrm{M}_{\odot}$. If the total mass of a cluster of 100 galaxies is $10^{15} M_{\odot}$, how much dark matter is contained in the cluster by the percentage of the total mass (ignoring the hot X-ray gas)?

Sunny Guha
Sunny Guha
Numerade Educator
01:56

Problem 5

Same as problem $4,$ but now the hot $X$ -ray gas has a mass 10 times greater than the galaxies. How much dark matter is contained in the cluster by the percentage of the total mass?

Sunny Guha
Sunny Guha
Numerade Educator
02:04

Problem 6

A spectral line of hydrogen has an absorption laboratory wavelength of $122 \mathrm{nm}$. It is observed in the spectrum of a quasar at $130 \mathrm{nm}, 180 \mathrm{nm},$ and $330 \mathrm{nm} .$ What are the redshifts $(z)$ of these clouds? What would be their distances, assuming Hubble's law (and using $V=c \times z$ )?

Suzanne W.
Suzanne W.
Numerade Educator