CH28

The rich galaxy cluster that is closest to our Local Group of galaxies is the

Virgo Cluster

How do astronomers know that there aren't significant amounts of dark matter within our solar system?

a lot of dark matter would affect the motions (orbits) of our spacecraft as the move through the solar system, and see no such effect

Roughly how many galaxies make up our Local Group?

about 60 or so

By examining rich clusters of galaxies, such as the Coma Clusters, astronomers have discovered that spiral galaxies

are found mostly in the outer regions of such clusters, not in the middle

When astronomers have examined rich clusters of galaxies with their instruments, they have found that these clusters

are more likely to contain giant elliptical galaxies than poor clusters

Some astronomers searching for what the mysterious "dark matter" might be made of have pinned their hopes on MACHO's (MAssive Compact Halo Objects). What do they think these MACHO's are?

black holes, brown dwarfs, and white dwarfs in the regions outside the main disk of our Galaxy

Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:

bluer and smaller

According to our current understanding, giant elliptical galaxies form:

by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies

Astronomers believe that the large elliptical galaxies formed

from the collision and merger of many smaller fragments

What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?

galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles

To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND

how far away from us each cluster was

Which of the following is a way that having an active galactic nucleus (AGN), with a supermassive black hole in the center, can affect the development of a galaxy?

huge energetic jets from the accretion disk can disturb and lessen star formation in the galaxy

If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?

in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away

The cosmological principle in astronomy

is confirmed by many observations done by Hubble and many other astronomers since

According to the Cosmological Principle, the universe

is isotropic and homogeneous

Which of the following is not true about the Local Group of galaxies (of which the Milky Way is a member)?

it has about a thousand member galaxies

According to our modern "bottom-up" model of the formation of large structures in the universe, the structures that formed first were about the mass of a

large globular cluster or a small galaxy

There is some irony in the fact that the Hubble Space Telescope has shown that Edwin Hubble's classification scheme for galaxy shapes only works in the later stages of the universe. What have really deep pictures (going way back in time) taken with the Hubble Telescope shown about galaxies long ago (in the first few billion years after the Big Bang)?

long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looks chaotic and lumpy

Which of the following does NOT happen when two galaxies collide?

many of the stars in one galaxy collide with the stars in the other

Which of the following is not a way that astronomers can find how much dark matter there is in cluster of galaxies?

observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them

Why do galaxies collide, while stars almost never do?

stars are much further apart (compared to how big they are) than galaxies are

The Sloan Digital Sky Survey

takes images and spectra of millions of objects, to find the positions and redshifts of as many galaxies and quasars as possible

If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would NOT be part of that address?

the Coma Cluster

How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy?

the amount of detectable matter is far less than the amount of dark matter & energy

Which of the following statements about our modern ideas of how spiral galaxies form and develop is TRUE?

the central bulges of spiral galaxies formed first and their disks formed later

An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?

the galaxy must have a lot of star formation going on at the time we are seeing it

If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:

the galaxy must have a lot of young stars and thus active star formation must still be going in it

With enormous effort, a team of astronomers manages to collect enough light from a galaxy far, far away to produce a spectrum. That spectrum has lines from the elements carbon, silicon, and sulfur. This tells the team that

the galaxy must have had an entire generation of stars that was born, lived, and died

An astronomer discovers a massive galaxy which has four nuclei. What is a likely explanation for a galaxy having more than one nucleus?

the galaxy must have swallowed several smaller galaxies that were its neighbors

In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?

the solar system

When astronomers say that the groups of galaxies are distributed isotropically, they mean that

the way galaxies are arranged in space looks the same in all directions

Astronomers can now report that active star formation was going on at a time when the universe was only 20% as old as it is today. When astronomers make such a statement, how can they know what was happening inside galaxies way back then?

they examine the spectra of galaxies (or the overall colors of galaxies) with the highest redshifts they can find

One important way astronomers can learn in some detail about what happens when galaxies collide is

to simulate galaxy collisions on a large computer and watch what the simulation predicts

The "great voids" that astronomers studying galaxies are finding are:

very large regions of intergalactic space, where relatively few galaxies or galaxy clusters can be found

Which of the following can we NOT learn from studying the Doppler shifts in the spectrum of galaxies beyond our Local Group?

whether they have Jupiter-mass planets around many of their stars