chap 28

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

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

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

Why do galaxies collide, while stars almost never do?

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

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

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

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

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