Download Lesson 3 - The Life Cycle of Stars - Hitchcock

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Observational astronomy wikipedia, lookup

Dyson sphere wikipedia, lookup

Corona Borealis wikipedia, lookup

Auriga (constellation) wikipedia, lookup

Corona Australis wikipedia, lookup

Serpens wikipedia, lookup

Boötes wikipedia, lookup

Star of Bethlehem wikipedia, lookup

Cassiopeia (constellation) wikipedia, lookup

Aquarius (constellation) wikipedia, lookup

CoRoT wikipedia, lookup

Perseus (constellation) wikipedia, lookup

Cygnus (constellation) wikipedia, lookup

Ursa Major wikipedia, lookup

Hipparcos wikipedia, lookup

Star catalogue wikipedia, lookup

Stellar classification wikipedia, lookup

Star wikipedia, lookup

Lyra wikipedia, lookup

Future of an expanding universe wikipedia, lookup

H II region wikipedia, lookup

Astronomical spectroscopy wikipedia, lookup

Corvus (constellation) wikipedia, lookup

Timeline of astronomy wikipedia, lookup

Ursa Minor wikipedia, lookup

Stellar kinematics wikipedia, lookup

Star formation wikipedia, lookup

Stellar evolution wikipedia, lookup

Transcript
Unit 1 Lesson 3 The Life Cycle of Stars
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
A Star Is Born
What is the life cycle of a star?
• Stars form in nebulae.
• A nebula is a large cloud of gas and dust. It is
composed mainly of hydrogen and helium, with
small amounts of heavier elements.
• An outside force, such as the explosion of a
nearby star, may cause the nebula to contract and
cool.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a star?
• As particles within the nebula are pulled closer
together, gravitational attraction increases.
• As a result, dense regions of gas and dust form
within the nebula.
• The densest regions, called dense cores, form new
stars.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a star?
• The temperature within dense cores increases for
millions of years.
• At about 10 million °C, the process of hydrogen
nuclear fusion begins, marking the birth of a star.
• A star can remain actively fusing hydrogen into
helium for billions of years. This stage ends when
the star runs out of hydrogen.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a star?
• Nuclear fusion happens in three steps.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a star?
• When nearly all the hydrogen in a star’s core has
fused into helium, the core contracts under its
own gravity and its temperature rises.
• Energy is transferred to a thin shell of hydrogen
surrounding the core, where hydrogen fusion
continues and the shell expands.
• When fusion ends completely, the star begins to
eject matter, until only the core remains.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
The Lightweights
What is the life cycle of a low-mass
star?
• The outward pressure generated by a star’s fusion
reaction is in balance with the inward gravitational
pull.
• When the active fusion stage ends, these forces
are no longer in balance, and the star’s outer
atmosphere expands.
• The gases in the outer shell grow cooler, and the
star is much larger and glows red. These large red
stars are called giants.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a low-mass
star?
• Giant stars shine brightly because of their large
surface areas.
• Giants are at least 10 times the size of the sun.
• Low-mass stars, which contain about as much
mass as the sun, will become red giants.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a low-mass
star?
• Over time, a giant’s outer gases drift away, and
the remaining core collapses, becoming denser
and very hot.
• A white dwarf is the hot, dense core of matter
that remains from the collapse of a low-mass star.
It is about the size of Earth.
• White dwarfs shine for billions of years, becoming
fainter as they cool. This is the final stage in the
life cycle of low-mass stars.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a low-mass
star?
• How does a low-mass star become a giant and
then a white dwarf?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
The Heavyweights
What is the life cycle of a high-mass
star?
• When hydrogen fusion in a high-mass star ends,
other types of fusion begin, producing elements
heavier than carbon.
• The star expands to become a supergiant.
• A star with 10 times the mass of our sun will
become a supergiant in just 20 million years.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a high-mass
star?
• In the supergiant stage, the high-mass star fuses
larger and larger nuclei until all its nuclear fuel is
used up.
• The core then rapidly collapses and heats up. This
halts the collapse, and the supergiant becomes a
supernova.
• A supernova is a gigantic explosion in which a
high-mass star collapses, throwing its outer layers
into space. But its core remains.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a high-mass
star?
• Compare the sizes of the sun and a high-mass
star.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a high-mass
star?
• As the core of a supernova continues to collapse,
its protons and electrons smash together to form
neutrons.
• The resulting neutron star is a small, incredibly
dense ball of closely packed neutrons.
• Neutron stars rotate very rapidly. Some emit a
rotating beam of electromagnetic radiation. These
stars are called pulsars.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a high-mass
star?
• Some supergiants are so massive that their cores
are unable to stop collapsing under the force of
gravity.
• As the core collapses, the mass of the star is
compressed into a single point, which is called a
black hole.
• A black hole is an invisible object with gravity so
great that nothing, not even light, can escape it.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
What is the life cycle of a high-mass
star?
• Although black holes are invisible, they can be
observed by the gravitational effect they have on
their surroundings.
• Matter swirls around a black hole just before being
pulled in. The matter becomes so hot that it emits
X-rays.
• Astronomers use X-rays and other means to
locate black holes, even within our own galaxy.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
A Graphic Display
How are stars plotted on the H-R
diagram?
• Astronomers refer to brightness as luminosity.
Luminosity is a measure of the total amount of
energy a star gives off each second.
• When the surface temperatures of stars are
plotted against their luminosity, a consistent
pattern is revealed.
• The graph that illustrates this pattern is called the
Hertzsprung-Russell diagram, or H-R diagram.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
How are stars plotted on the H-R
diagram?
• The hottest stars are located on the left side of
the H-R diagram and are blue.
• The coolest stars are located on the right side of
the diagram and are red.
• The brightest stars are located at the top of the
diagram, and the dimmest stars are located at the
bottom.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
How does the H-R diagram show
different life cycle stages?
• The temperature and luminosity of most stars fall
within a band that runs diagonally through the
middle of the H-R diagram.
• This band, called the main sequence, is the
region of the diagram where stars spend most of
their lives.
• Stars within this band are actively fusing
hydrogen and are called main-sequence stars.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
How does the H-R diagram show
different life cycle stages?
• The sun is a main-sequence star.
• When nuclear fusion ends in the sun, it will
become a giant and will move to the upper right
quadrant of the H-R diagram.
• When the outer layers of the giant are lost to
space, the sun will become a white dwarf and
move to the lower left quadrant of the diagram.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 1 Lesson 3 The Life Cycle of Stars
How does the H-R diagram show
different life cycle stages?
• Locate the positions of the brightest stars and the
coolest stars on the diagram.
Copyright © Houghton Mifflin Harcourt Publishing Company