Download The Life Cycle of Stars Stars are a fascinating part of our universe

The Life Cycle of Stars
Stars are a fascinating part of our universe. The may seem like a permanent part of the night sky but they actually are not.
Stars don’t “live” forever; they only exist for specific periods of time. The life cycle of a star is similar to the life cycle of
many living things. They are born. They “grow up.” They exist for many years, and then they die.
Comparison diagram of Human Lifetime and Star Lifetime – They share similar phases in their live
http://science89.wordpress.com/2009/05/20/life-cycle-of-a-star/
The life of a star begins in a cloud of dust and gas known as the nebula. The nebula is composed primarily of Hydrogen
(97%) and Helium (3%) gas. Gravity causes the dust and gas to clump together. The number of atoms in the clump
increases and the mass of the clump increases. This initial mass determines the mass of the star. As the gravitational
attraction in the nebula grows the clump contracts and flattens into a spinning disk. This spinning disk becomes
extremely hot and forms a glowing protostar. Once the protostar reaches critical temperatures, nuclear fusion begins.
Nuclear fusion in the protostar is when hydrogen atoms combine to form helium atoms. This fusion reaction signals the
birth of a star. It’s the release of energy during nuclear fusion that causes a star to shine!
After a star is born, it enters the main sequence phase of its life. The amount of time a star remains in the main sequence
phase depends upon its mass. Smaller stars remain here much longer than larger stars. The main sequence stage is the
longest stage in star’s life cycle. Small stars can remain here for billions of years fusing hydrogen into helium while
larger stars remain for only millions of years. Smaller stars fuse atoms much slower than larger stars and therefore live
much longer lives.
As stars “age,” the outer layers of gas are pushed out into space. They grow like an expanding, glowing ball. This can
make the star very luminous (bright), but the expanding shell cools and the temperature of the star decreases. These
expanding stars enter “old age” and leave the main sequence. Smaller stars become red giants, while larger stars become
super giants.
Once the atoms in a red giant are depleted (used up), the star collapses under the force of gravity and becomes an
extremely hot white dwarf.
Super giants begin to rapidly combine carbon atoms together to form iron. This fusion reaction causes the super giant to
lose massive amounts of energy. The force of gravity becomes too great and the core of the star collapses in a violent
explosion known as the supernova. After the supernova either a neutron star or a black hole will form. A neutron star is
a small hot core made entirely of neutrons. If the star is extremely large however, it will be swallowed up by its own
gravity and collapse into a black hole. A black hole has such a strong gravitational pull that not even light can escape it!
Picturing the Life Cycle of a Star
The H-R Diagram
Understanding the Relationship between the Temperature and Luminosity of a Star
The H-R diagram shows you the relationship between the luminosity (brightness) and temperature of a star. The Sun, like
90% of all stars, is a main sequence star. The other stars fall into three regions on the H-R diagram. The red giants and
super giants lie above the main sequence line. Red giants have large diameters with lower temperatures. Super giants are
very large and have varying temperatures. White dwarfs lie below the main sequence stars. They are very hot and have
small diameters in comparison to most main sequence stars.
The Life & Death of a Star
Introduction: You are a movie producer; your job is to make a documentary film about the life story of a star
from birth to death.
Standard 4(b): Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may
differ in size, temperature, and color.
Directions: You will be given a film strip template. In this template you will have to draw each stage in the life
of a star. You will also have to write a mini summary explaining what happens in that stage. Your summaries
should discuss the relative size, temperature and color of the stars formed. The life stages of stars include the
nebula, protostar, main sequence, giant, white dwarf, super giant, supernova, neutron star, and black hole.
1. Step 1 – Center Frame - Title
a. Create a Title for your movie . Be creative and make up your own unique title.
b. Write “produced by” and your name.
c. Draw and color a picture of the nebula.
d. Write a summary that defines the nebula, discusses its composition, and the role of gravity in the
formation of stars
2. Step 2 – Protostar Frame
You will make two Protostar frames. They go on each side of the Nebula.
Protostar
3.
4.
5.
6.
7.
Nebula
Protostar
a. Title this frame: Protostar.
b. Draw and color a picture of the protostar
c. Write a summary that defines protostar and discuss. (Yes, you are doing this step twice.)
Step 4 - Main Sequence – one direction from center
a. Title this frame Main Sequence Star
b. Draw and color a picture of a main sequence star.
c. Write a summary that identifies and explains whether or not this is a low mass or a high mass
star. Defines a main sequence star. Give an example.
Step 5 – Giant
a. Title this frame Giant Star
b. Draw and color a picture of a Giant star.
c. Write a summary that defines a Giant star, describes why it is this color, and explains how a star
becomes a Giant.
Step 6 – White Dwarf
a. Title this frame White Dwarf
b. Draw and color a picture of a White Dwarf.
c. Write a summary that defines a White Dwarf, describes why it is this color, and explains how a
star becomes a White Dwarf.
Step 4 - Main Sequence – one other direction from center
a. Title this frame Main Sequence Star
b. Draw and color a picture of a main sequence star.
c. Write a summary that identifies and explains whether or not this is a low mass or a high mass
star. Defines a main sequence star. (Yes, you are doing this step twice.)
Step 7 – Super Giant
a. Title this frame Super Giant
b. Draw and color a picture of a Super Giant.
c. Write a summary that defines a Super Giant, describes the color, and explains how a star
becomes a Super Giant
8. Step 8 – Supernova
a. Title this frame Supernova
b. Draw and color a picture of a supernova.
c. Write a summary that defines a supernova and explains how a star becomes a Supernova
9. Step 9 – Neutron Star
a. Title this frame Neutron Star
b. Draw and color a picture of a Neutron star.
c. Write a summary that defines a Neutron and explains how a Neutron is different from a normal
star
10. Step 10 – Black Hole
a. Title this frame Black Hole
b. Draw and color a picture of a Black Hole
c. Write a summary that defines a Black Hole and explains how a Neutron Star becomes a Black
Hole
Additional Details






Use pencil first for pictures – You W ILL NOT be given more templates.
Be neat
Color each frame with detail
Fill up the frame. Do not draw a tiny picture.
Write your explanation first on paper. Only write the final draft on the template - You W ILL NOT be
given more templates.
Double check your facts with the in-class handout and your text book chapter 12 section 2.