Download Life Cycle of a Star

Bellwork
• 1. Define AU
• 2. What do we call the 3 Laws of
Planetary Motion?
Chapter 3 Section 4
Planetary Motion Review
• Visual Concepts online
• Ch3Sec4 Planetary Motion worksheet
Create a Chart
In your note book create a KWL chart and write
what you know about how stars are formed. Also
summarize what you know about the life cycle of
a star? Next fill in the W.
K
W
L
What do you know? What do you want to know? What did you learn?
Objectives
• Describe the different types of stars
• Describe how color indicates the
temperature of a star
• Describe the quantities that are plotted in
the H-R diagram
Chapter 2: Section 2&3
How is a
star born?
• begins as a ball of gas and
dust
• Gravity causes the debris to
form a sphere
• As it gets denser it becomes
hotter creating the right
setting for nuclear fusion to
occur.
• Hydrogen begins to change
into Helium
The Birth of a Star
Life Cycle of
a Star:
- Stars are classified by
their size, brightness,
color, temperature,
spectrum and age.
- Stars progress
through the same life
cycle, but the larger,
hotter, and brighter
stars progress much
faster.
Life cycle sequence
• Stars begin as a large cloud of gas
and dust called a nebula
• Once stars are formed they enter
the main sequence stage. In this
stage they continuously generate
energy in the core through nuclear
fusion.
• Size, structure and composition
change very little during this stage.
A Tool for Studying Stars
• The H-R diagram is a
graph that shows the
relationship between a
star’s surface temperature
and its absolute
magnitude.
The Hertzsprung Russell Diagram
HR Diagram: The abundance of main sequence stars
Life sequence continued…
• The third stage occurs when a star becomes
a Red Giant or a Red Super Giant.
• This occurs when a star has used all of it’s
hydrogen and begins to expand and cool.
This causes the core to shrink, which then
causes the rest of the sun’s atmosphere to
expand.
• Red Giants can about ten times larger than
the sun.
• Super giants are at least 100 times larger
than the sun.
Important terms
• Nebula
• Main
sequence
• Red/Super
Giant
• Ball of dust and gas- beginning
of a star.
• Constant Energy generated
through nuclear fusion. The
longest stage of a star.
• A star that is expanding and
cooling; hydrogen is no longer
generating energy. 10x larger
/100x larger than sun.
Betelgeuse star
Betelgeuse is a red super giant
Life sequence continued…
• The final stage of a star’s life cycle is a
white dwarf.
• A white dwarf is an old star’s leftover
center that is no longer generating
energy (no hydrogen left)
• White dwarfs can shine for billions of
years before cooling completely
White Dwarfs
Life cycle of a Star:
Death of a Star
• Stars usually lose material slowly
unless they are blue stars.
• Blue stars lose their energy fast
and can sometimes explode in a
bright flash called a Supernova,
which is actually the collapse of
the star.
Death of a Stars
Super Novas can become:
Neutron starsstars that have collapsed under gravity
Pulsar stars –
-spinning neutron stars that have jets of particles
moving almost at the speed of light streaming out
above their magnetic poles.
-The beams of light sweep around as the pulsar
rotates, just as the spotlight in a lighthouse does.
-Like a ship in the ocean that sees only regular
flashes of light, we see pulsars turn on and off as the
beam sweeps over the Earth.
-This along with the light being refracted by Earth’s
atmosphere creates a stars “Twinkling” appearance
Neutron Stars and Blackholes
Interesting trivia
• Pulsars spin fast for the same reason ice
skaters pull in their arms to spin. This is
conservation of angular momentum. Pulsars
are formed with a certain amount of angular
momentum. As gravity causes them to
shrink (and thus have a smaller radius) they
must spin faster in order to conserve angular
momentum.
http://imagine.gsfc.nasa.gov/docs/science/tr
y_l1/pulsar.html
Black Holes
• Leftover supernovas that are so
massive they collapse into an object
called a black hole
• Light can not escape a black holes
gravity because it is so massive
• They are only detected through x-rays
that can determine a black hole
through materials from stars filtering
through it
Myths vs. realities of black holes
Hubble Space Telescope
•
Important terms
• Final stage, no hydrogen left.
Can shine for billions of yrs.
• Blue stars that explode in a
Supernova
bright flash.
• Stars that collapse from the
Neutron/Pulsar gravity-pulsars spin.
star
White Dwarf
Black hole
• Leftover supernovas that
collapse into themselves
forming gravity so massive
that no light can escape.
• This artist's concept depicts a super massive
black hole at the center of a galaxy. NASA's
Galaxy Evolution Explorer found evidence that
black holes -- once they grow to a critical size - stifle the formation of new stars in elliptical
galaxies. Black holes are thought to do this by
heating up and blasting away the gas that fuels
star formation.
• The blue color here represents radiation
pouring out from material very close to the
black hole. The grayish structure surrounding
the black hole, called a torus, is made up of gas
and dust. Beyond the torus, only the old redcolored stars that make up the galaxy can be
seen. There are no new stars in the galaxy.
Image Credit:
• NASA/JPL-Caltech
Color of Stars
• What Is the Color of Hot?
Although red and yellow may
be thought of as “warm” colors
and blue may be thought of as
a “cool” color, scientists
consider red and yellow to be
cool colors and blue to be a
warm color.
Stellar Spectrum
How Bright Is That Star?
• Apparent Magnitude The brightness
of a light or star is called apparent
magnitude. How luminous the star is as
it is viewed from Earth.
• Absolute Magnitude Absolute
magnitude is the actual brightness of a
star. Measurement of stars luminosity
when placed at the same distance,
absolute magnitudes show differences in
actual luminosities.
Brightness and Luminosity
The H-R diagram is a graph that shows
the relationship between a star’s surface
temperature and its absolute magnitude.
Objectives
• Describe the different types of stars
• Describe how color indicates the
temperature of a star
• Describe the quantities that are plotted in
the H-R diagram