Transcript Section 4 Formation of the Universe Chapter 19

Chapter 19
Stars, Galaxies, and the Universe
Table of Contents
Section 2 The Life Cycle of Stars
Section 3 Galaxies
Section 4 Formation of the Universe
Chapter 19
Section 1 Stars
Color of Stars
• Because a blue flame is hotter than a yellow or
red flame, we can conclude that blue stars are
hotter than yellow or red stars.
Chapter 19
Section 1 Stars
Composition of Stars
• A star is made of different elements in the form of
gases.
• The gases in the atmosphere of a star absorb
different wavelengths of light depending on which
elements make up the gases.
• The light from a star indicates which elements
make up that star.
Chapter 19
Section 1 Stars
Composition of Stars continued
• The Colors of Light A prism breaks white light
into a rainbow of colors called a spectrum.
• An instrument called a spectrograph is used to
break a star’s light into a spectrum. The spectrum
of a star will vary depending on which elements are
present.
Chapter 19
Section 1 Stars
Classifying Stars
•Differences in Temperature Stars are now
classified by how hot they are.
• Differences in Brightness The brightest star,
Sirius, has a magnitude of -1.4. The dimmest star
that can be seen with a microscope has a
magnitude of 29.
Chapter 19
Section 1 Stars
Distance to the Stars
• Because stars are so far away, astronomers use
light-years to measure the distances from Earth to
the stars. A light year is the distance that light
travels in a year.
Chapter 19
Section 2 The Life Cycle of Stars
Bellringer
Supernovas represent the “death” of stars that
exceed a certain mass. In a few seconds, a
supernova can release more energy than it previously
did in its entire existence. Look at the photographs of
Supernova 1987A and the Large Magellanic Cloud
taken before the explosion.
Record and illustrate your answers in your science
journal.
Chapter 19
Section 2 The Life Cycle of Stars
Objectives
•Describe different types of stars.
• Describe the quantities that are plotted in the H-R
diagram.
• Explain how stars at different stages in their life
cycle appear on the H-R diagram.
Chapter 19
Section 2 The Life Cycle of Stars
The Beginning and End of Stars
• The Beginning A star enters the first stage of its
life cycle as a ball of gas and dust. Gravity pulls the
gas and dust together, and hydrogen changes to
helium in a processes called nuclear fusion.
• The End Stars usually lose material slowly, but
sometimes they can lose material in a big explosion.
Much of a star’s material returns to space, where it
sometimes forms new stars.
Chapter 19
Section 2 The Life Cycle of Stars
Different Types of Stars
• Stars can be classified by their size, mass,
brightness, color, temperature, spectrum, and age. A
star’s classification can change as it ages.
• Main-Sequence Stars After a star forms, it enters
the second and longest stage of its life cycle known
as the main sequence. Energy is generated in the
core as hydrogen atoms fuse into helium atoms.
Chapter 19
Section 2 The Life Cycle of Stars
Different Types of Stars, continued
• Giants and Supergiants After the main-sequence
stage, a star can enter the third stage of its life cycle.
A red giant, as it is know known, is a large, reddish
star late in its life cycle.
• In this third stage, a star can become a red giant. As
the center of the star shrinks, the atmosphere of the
star grows very large and cools to form a red giant or
a red supergiant.
Chapter 19
Section 2 The Life Cycle of Stars
A Tool for Studying Stars
•The H-R Diagram the Hertzprung-Russell diagram is
a graph that shows the relationship between a star’s
surface temperature and absolute magnitude.
• Reading the H-R Diagram The diagonal pattern on
the H-R diagram where most stars lie is called the
main sequence. Find the diagonal pattern in the H-R
Diagram on the next two slides.
Chapter 19
Section 2 The Life Cycle of Stars
H-R Diagram
Chapter 19
Section 2 The Life Cycle of Stars
Chapter 19
Section 2 The Life Cycle of Stars
When Stars Get Old
• Supernovas A supernova is a gigantic explosion in
which a massive blue star collapses.
• Neutron Stars and Pulsars A star that has
collapsed under gravity to the point at which all of its
particles are neutrons is called a neutron star. If a
neutron star is spinning, it is called a pulsar.
Chapter 19
Section 2 The Life Cycle of Stars
When Stars Get Old, continued
• Black Holes Sometimes the leftovers of a
supernova are so massive that they collapse to form a
black hole. A black hole is an object that is so
massive that even light cannot escape its gravity.
Chapter 19
Section 3 Galaxies
Bellringer
Look at the photograph of a spiral galaxy.
• Describe the evidence that indicates that the
galaxy is rotating.
• What other objects have you seen look similar to a
spiral galaxy? Do they rotate?
Record your answers in your science journal.
Chapter 19
Section 3 Galaxies
Objectives
• Identify three types of galaxies.
• Describe the contents and characteristics of
galaxies.
• Explain why looking at distant galaxies reveals
what young galaxies looked like..
Chapter 19
Section 3 Galaxies
• A galaxy is a collection of stars, dust, and gas held
together by gravity.
Types of Galaxies
• Spiral Galaxies have a bulge at the center and
spiral arms.
• The Milky Way Astronomers think that our solar
system is in a spiral galaxy.
Chapter 19
Section 3 Galaxies
Types of Galaxies, continued
• Elliptical Galaxies About one-third of all galaxies
are simply massive blobs of stars. These are called
elliptical galaxies.
• Irregular Galaxies Galaxies that do not fit into any
other class are called irregular galaxies.
Chapter 19
Section 3 Galaxies
Contents of Galaxies
• Gas Clouds A large clouds of gas and dust in
interstellar space is called a nebula.
• Star Clusters A globular cluster is a tight
group of stars that looks like a ball and contains
up to 1 million stars.
• An open cluster is a group of stars that are
close together relative to surrounding stars.
Chapter 19
Section 3 Galaxies
Chapter 19
Section 3 Galaxies
Origin of the Galaxies
• Because if takes light time to travel through space,
looking at distant galaxies reveals what early galaxies
looked like.
• Quasars A very luminous, starlike object that
generates energy at a high rate is called a quasar.
Some scientists think that quasars may be the core of
young galaxies that are in the process of forming.
Chapter 19
Section 4 Formation of the Universe
Bellringer
Look at Figure 1. The first image represents the
initial explosion of the big bang, and the following
images represent the expansion of the universe and
the formation of the galaxies.
Describe the differences between the images.
Record your answers in your science journal.
Chapter 19
Section 4 Formation of the Universe
Objectives
• Describe the big bang theory.
• Explain evidence used to support the big bang
theory.
• Describe the structure of the universe.
Chapter 19
Section 4 Formation of the Universe
Objectives, continued
• Describe two ways scientists calculate the age of
the universe.
• Explain what will happen if the universe expands
forever.
Chapter 19
Section 4 Formation of the Universe
• Cosmology is the study of the origin, properties,
processes, and evolution of the universe.
Universal Expansion
• Galaxy Movement To understand how the universe
formed, scientists study the movement of galaxies.
• A Raisin-Bread Model The universe, like the rising
raisin bread dough, is expanding. Think of the raisins
in the dough as galaxies. As the universe expands, the
galaxies move farther apart.
Chapter 19
Section 4 Formation of the Universe
Universal Expansion
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Visual Concept
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Chapter 19
Section 4 Formation of the Universe
The Big Bang Theory
• A Tremendous Explosion The theory that the
universe began with a tremendous explosion is called
the big bang theory.
• Cosmic Background Radiation In 1964, two
scientists using a huge antenna accidentally found
radiation coming from all directions in space. One
explanation for this radiation is that it is cosmic
background radiation left over from the big bang.
Chapter 19
Section 4 Formation of the Universe
Big Bang Theory
Chapter 19
The Structure
of the Universe
Section 4 Formation of the Universe
Chapter 19
Section 4 Formation of the Universe
How Old Is the Universe?
• Age of the Universe Scientist use to methods to
study the age of the universe.
• By measuring the distance between Earth and
various galaxies, scientists can predict the rate of
expansion and calculate the age of the universe.
• Because the universe must at least be as old as the
oldest stars it contains, the ages of the stars provide a
clue to the age of the universe.
Chapter 19
Section 4 Formation of the Universe
A Forever Expanding Universe
• The expansion of the universe depends on the
amount of matter it contains. A large enough quantity
of matter would cause gravity to stop the expansion.
The universe could start collapsing.
• Scientist now think that there may not be enough
matter in the universe, so the universe would continue
to expand forever and become cold and dark as all the
stars die.
End of Chapter 19