Download Evolution of a Star

Evolution of a Star
Objectives
• Students will be able to identify and describe the evolution of a star.
Suggested Grade Level
Ninth Grade
Subject Area(s)
Science
Language Arts
Timeline
Two 50-minute class periods
Background
We have a theory of how stars evolve, what makes them different from one
another and what happens when they die.
Teachers - Stars begin as a large cloud of dust and gas called a nebula. The
particles of dust and gas exert a gravitational force on each other causing the
nebula to contract. As the particles move closer together, the temperatures
increase. When the temperature in the nebula reach 10 000 000K, fusion
begins. The energy that is released radiates outward through the condensing
ball of gas. A star is born!
The life of a star depends greatly on its mass.
Protostar is a period after clouds of hydrogen, helium, and dust begin to contract
and before the star reaches the main sequence. A protostar forms from the
contraction within a giant molecular cloud in the interstellar medium. Protostars
of around the mass of the Sun typically take 10 million years to evolve from a
condensing cloud to a main-sequence star. A protostar of 15 solar masses
evolves much more quickly, typically taking only 100,000 years to reach the main
sequence.
The heat from fusion causes pressure that balances the attraction due to gravity
and a star becomes a main sequence star. About 90% of all stars are main
sequence stars. Most of the stars are small red stars found in the lower right of
the H-R diagram. Hot blue bright stars are in the upper left of the H-R diagram.
Among the main sequence stars, the hottest stars generate the most light and
the coolest generate the least. Our sun is a yellow main sequence star.
When the hydrogen in the core of the star is all gone, there is no balance
between pressure and gravity. The core contracts and the temperatures inside
the star increase. This causes the outer layers of the star to expand. The star
has evolved into a giant. If the star equals one solar mass, then it becomes a red
giant. If the star equals 100 solar masses, then it will become a supergiant. In
about 5 billion years, our sun will become a giant.
Once the red giant’s core uses its supply of helium, it contracts even more. As
the core runs out of fuel, the outer layers escape into space. This leaves behind
the hot dense core. The core contracts under the force of gravity. At this stage
in a star’s evolution, it is a white dwarf. A white dwarf is about the size of the
Earth.
In stars that are over ten times more massive than our sun, the stages of
evolution are quicker and more violent. The core heats up to a much higher
temperature. Heavier elements form by fusion. The star expands into a
supergiant. Eventually, iron forms in the core. Fusion can no longer occur. The
core collapses violently, sending a shock wave outward through the star. The
outer portion of the star explodes, producing a supernova. The supernova can
be millions of time brighter than the original star.
The collapsed core of a supernova shrinks to 10-15 km. Only neutrons can exist
in the dense core and supernova becomes a neutron star.
If the remaining dense core is over three times more massive than the sun,
nothing can stop the core’s collapse. It quickly evolves into a black hole – an
object so dense nothing can escape its gravity field.
Students – Know the background of the above elements.
Materials
Pencil
Lined-paper
A set of pictures (Set A/Set B)
Textbook
Class notes
Lesson
1. Vocabulary
Star - A self-luminous celestial body consisting of a mass of gas held
together by its own gravity in which the energy generated by nuclear
reactions in the interior is balanced by the outflow of energy to the
surface, and the inward-directed gravitational forces are balanced by
the outward-directed gas and radiation pressures.
Prostar - is a period after clouds of hydrogen, helium, and dust begin to
contract and before the star reaches the main sequence.
Nebula - A diffuse mass of interstellar dust or gas or both, visible as
luminous patches or areas of darkness depending on the way the
mass absorbs or reflects incident radiation.
2.
3.
4.
5.
6.
Interstellar medium - interstellar space including streams of protons
moving from the stars.
Fusion - The act or procedure of liquefying or melting by the
application of heat.
Supernova - A rare celestial phenomenon involving the explosion of
most of the material in a star, resulting in an extremely bright, shortlived object that emits vast amounts of energy.
Students will work in pairs to take a set of pictures of various stars and
place them in the correct order of evolution. Some students will
receive Set A (less massive) and some students will receive Set B
(more massive). Note: The teacher will need to assemble the sets
before the lesson.
Once the students think they have the correct order the students will
check with the teacher.
Once each pair has the correct order, they will use their class notes
and textbook to write a paragraph to describe what is going on in each
picture. (Each picture will have a paragraph.)
Each pair with Set A pictures will find a pair with Set B pictures and
place each others cards in order.
The group will write a paragraph that compares and contrasts the two
sets of cards.
Extensions
1. Compare various stars (Vega, Sirius, etc.) to our sun.
Evaluation/Assessment
• Students were able to identify and describe the evolution of a star.
• Students were able to place the cards in the correct order.
• Students write individual paragraphs for each picture that describes the
evolution of a star that contains the information from the background
section.
• Students as a group write a paragraph that compares and contrasts the
two sets of cards.
Resources
Glencoe Earth Science. New York: Glencoe/McGraw Hill, 1997. ISBN 0-02827809-7.
The American Heritage Dictionary
Space Foundation Corse: Astronomy Principles for the Classroom, Graduate
Course, Space Foundation.
http://www.nmm.ac.uk/upload/img/2_20020624101618.jpg
http://www.american-buddha.com/supernova.4.jpg
http://images.google.com/imgres?imgurl=http://www.pbs.org/wnet/hawking/strang
e/assets/images/ss.nebulae.jpg&imgrefurl=http://www.pbs.org/wnet/hawking/stra
nge/html/strange_nebulae.html&h=222&w=280&sz=9&tbnid=ZNTB3PQoEx6CM:&tbnh=86&tbnw=109&hl=en&start=5&prev=/images%3Fq%3
Dnebulae%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF8%26sa%3DN
http://images.google.com/imgres?imgurl=http://www.eso.org/outreach/pressrel/pr-2004/images/phot-34e-04normal.jpg&imgrefurl=http://www.eso.org/outreach/press-rel/pr-2004/phot-3404.html&h=894&w=800&sz=728&tbnid=uAiBDToMh4yJM:&tbnh=145&tbnw=129&hl=en&start=13&prev=/images%3Fq%3Dnebula
e%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN
http://images.google.com/imgres?imgurl=http://www.clarkplanetarium.org/distribu
tion/Images/Stars/008_ProtoStar.jpg&imgrefurl=http://www.clarkplanetarium.org/
distribution/Stars.htm&h=150&w=225&sz=18&tbnid=5n9X4hzJ9yqaM:&tbnh=68&tbnw=102&hl=en&start=36&prev=/images%3Fq%3D
protostar%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DU
TF-8%26sa%3DN
http://images.google.com/imgres?imgurl=http://www.alienangels.hu/Pic1/blackhol
e.jpg&imgrefurl=http://www.alienangels.hu/9.szam.htm&h=226&w=300&sz=30&t
bnid=80kagpLEMyZLKM:&tbnh=83&tbnw=111&hl=en&start=21&prev=/images%
3Fq%3Dblackhole%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%2
6ie%3DUTF-8%26sa%3DN
http://images.google.com/imgres?imgurl=http://www.astro.princeton.edu/~frei/Gc
at_htm/Catalog/CJpeg/n2768.jpg&imgrefurl=http://www.astro.princeton.edu/~frei/
Gcat_htm/Sub_sel/gal_2768.htm&h=313&w=313&sz=11&tbnid=F_ojuGQ8822gE
M:&tbnh=113&tbnw=113&hl=en&start=7&prev=/images%3Fq%3Dsupergiants%2
6svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DG
http://images.google.com/imgres?imgurl=http://physics.uoregon.edu/~jimbrau/Br
auImNew/Chap20/FG20_13.jpg&imgrefurl=http://physics.uoregon.edu/~jimbrau/a
str122/Notes/Chapter20.html&h=599&w=599&sz=33&tbnid=j1hUMuZgBe875M:&
tbnh=133&tbnw=133&hl=en&start=16&prev=/images%3Fq%3Dwhite%2Bdwarf%
26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DG
http://isc.astro.cornell.edu/~sloan/fun/star.html
http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter20.html
http://en.wikipedia.org/wiki/Protostar
http://stardate.org/resources/gallery/gallery_detail.php?id=146
http://spaceinfo.jaxa.jp/note/hoshi/e/hos01_e.html
http://www.windows.ucar.edu/tour/link=/the_universe/HD93129A.html
Addendums
Pictures to make the sets of cards.
Red giant (Set A)
Supernova (Set B)
Nebulae (Set A)
Nebulae (Set B)
Protostar (Set A)
Protostar (Set B)
Blackhole (Set B)
Supergiant (Set B)
White Dwarf (Set A)
Neutron star (Set B)
Set A
Massive Main Sequence Star (Set B)