Download Name ______KEY Date Core ______ Study Guide Galaxies and the

Name _______KEY________________________ Date ______________ Core _________
Study Guide
Galaxies and the Expanding Universe
Give the definitions of the following:
Galaxy: a huge group of stars, gas and dust held together by gravity
Quasar: a very bright center of a galaxy. Shortened for quasi-stellar “seeming like a star”
Black Hole: Most large galaxies seem to have supermassive black holes at the center with a large mass.
It’s invisible because the gravity is too strong and it draws a large whirlpool of gas from nearby stars
which become compressed and very hot, giving off a bright light.
Universe: space and all of the matter and energy within it.
Explain: (in your own words!!!)
Why can’t we see all of the Milky Way from Earth? The Earth is inside the disk of the Milky Way so we
only have an edge view and can only view part of it. You can’t see the center of the galaxy because it’s
hidden by the dust – also, we can only see a small fraction of the stars because of they’re too far away.
How do astronomers detect black holes? Behavior of matter around the black hole identifies its presence.
The gravity pulls in gas which becomes compressed and hot, giving off bright light. The motion of stars
orbiting the black hole also shows something is there.
Why does the Milky Way looks like a hazy band of stars in the sky? The Milky Way is a band of blended
stars and we are viewing it from the edge so it’s impossible to see all of the stars.
What is the role of gravity within a galaxy? Gravity is the pulling force that holds the gas, dust, rocks
together – toward the center. The force is proportional to the mass. The larger mass will have a larger
pull/gravity.
How can astronomers learn about the past by looking at distant galaxies? Because of the time it takes for
the light from stars and other galaxies to reach the earth, we are actually looking in the past. The closest
star to earth is 4 light years away.
When did the Big Bang happen and what has happened since? The big bang theory is theorized to have
happened 14 billion years ago when the universe suddenly began to expand from one merged mass of
matter or substance. At that time, all matter was dense and hot and the universe developed in less than a
second. 300,000 years later, the first elements formed, then stars, planets and galaxies the next billion
years. At this time, the universe continues to expand.
Define and diagram the following:
SPIRAL GALAXIES: have arms of stars, gas, dust that curve away from the center of the galaxy in a
spiral pattern. They are disk shaped with a central bulge which are old stars. The dense spiral arms
contain many young, bright stars.
ELLIPTICAL GALAXIES: are shaped like spheres, eggs or circles. They have almost no dust or gas
between stars and their stars are old.
IRREGULAR GALAXIES: faint galaxies without a definite shape, are smaller with fewer stars.