Exam 17: The Cosmic Web: the Large-Scale Structure of the Universe

How large,in terms of number of galaxies,radius,and mass,is a typical galaxy group?

An astronomer would like to study a region of the Universe 100 Mpc across and 1 Gpc away from Earth,situated behind an obscuring cloud of dust,so he or she cannot directly measure light from the region.How could he or she measure the mass contained in this region?

An astronomer observes a galaxy that is currently 1 billion light years away from us.Does he or she see the galaxy as it was 1 billion years ago,or is the look-back time greater than or less than that number? Explain your reasoning.

The Local Group has about 50 galaxies in a region 2 Mpc across,while the Virgo Cluster has about 1,500 galaxies in a region 5 Mpc across.How do the densities of these systems compare?

Why did the first generation of stars to form in the Universe differ from those in the Milky Way?

How is matter distributed on the largest scales in our Universe?

If an astronomer looked at the field shown in the image below with an X-ray telescope,what would he or she see?

An astronomer discovers a region of space in which all the galaxies have peculiar motions away from a central point.This region is:

What drives structure formation in our Universe?

Why are most galaxies inside clusters ellipticals or lenticular galaxies?

Which nearby object has at least 1,300 galaxies in a region about 5 Mpc across?

Why do many galaxies that are gravitationally lensed by galaxy clusters look like arcs of a circle?

Hubble originally measured the value of Hubble's constant to be about 500 km/s/Mpc.The currently accepted value is about 70 km/s/Mpc,while the currently accepted age of the Universe is about 14 Gyr.What would Hubble have estimated the Universe's age to be?

What is the typical environment of a spiral galaxy?

What physical principle is most responsible for galaxies forming disks?

A galaxy cluster consists of 1,000 galaxies within a radius of 2.5 Mpc,traveling at a typical velocity of 1,000 km/s.If the average stellar mass of a cluster galaxy is 10¹¹ M_Sun,what fraction of the cluster's mass is NOT stellar?

An astronomer observes three large spiral galaxies within a radius of 1 Mpc of each other.This is most likely a galaxy:

Why do astronomers refer to the Dark Ages as "dark"?

What does it mean when astronomers say that dark matter is "cold"?

Two galaxy clusters have identical radii,but the galaxies in cluster A have a typical orbital velocity of 700 km/s,while the galaxies in cluster B have a typical velocity of 1,400 km/s.How do the masses of these clusters compare to each other?