Chapter 25 Pretest: Galaxies and the Universe

What is a galaxy?

• A small group of stars that, from Earth, appear to be arranged in a recognizable pattern

• A cloud of dust and gas in interstellar space

• A powerful gravitational field from which no light can escape

• A collection of billions of stars, gas, and dust held together by gravity

In what galaxy is Earth located?

• The Milky Way

• Andromeda

• The Kuiper belt

• Orion’s belt

Objects in our galaxy revolve around a common center of gravity, much like the planets in our solar system revolve around the sun.

• True

• False

How many galaxies are in the universe?

• hundreds

• thousands

• millions

• billions

Which event do scientists associate with the beginning of the universe?

• the supernova

• the big bang

• the main sequence

• the event horizon

What do most scientists think about the observable universe?

• It is shrinking in size.

• It is expanding in size.

• It is fixed in size.

• Its size is changing differently in different directions.

What do scientists think about the age of the universe?

• It is about 2 billion years old.

• It is about 4.6 billion years old.

• It is about 13.8 billion years old.

• It is eternal, so it has no age.

Which objects are considered the highest-energy objects in the universe?

• pulsars

• quasars

• galaxies

• galactic halos

What accounts for most of the matter in the universe?

• planets and moons

• stars

• dark matter

• supermassive black holes

Which statements are true of quasars? Select all correct answers.

• A. They emit large bursts of energy.

• B. They are relatively young.

• C. They are extremely distant from Earth.

• D. They are larger than galaxies.

• E. They provide clues about the early universe.