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Warm Up 6/6/08
1)
2)
3)
If star A is farther from Earth than star B, but both stars have the
same absolute magnitude, what is true about their apparent
magnitude?
a. Star B has the greater apparent magnitude.
b. Both stars have the same apparent magnitude.
c. Star A has the greater apparent magnitude.
d. Apparent magnitude is not related to distance.
A Hertzsprung-Russell (H-R) diagram shows the relationship
between ____.
a. temperature and absolute magnitude
b. apparent magnitude and parallax
c. absolute magnitude and apparent magnitude
d. parallax and temperature
Which of the following refers to the change in wavelength that
occurs when an object moves toward or away from a source?
a. spectroscopy
c. wave theory of light
b. Doppler effect
d. chromatic aberration
Answers: 1) a. 2) a. 3) b.
Stellar Evolution
Chapter 25, Section 2
The Birth of a Star
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The birthplaces are dark, cool interstellar
clouds (nebulae)
The initial contraction of the nebula can be
triggered by the shock wave from an explosion
of a nearby star
Once this begins, gravity squeezes the
particles, pulling every particle toward the
center
The Birth of a Star
The Orion Nebula in
normal color and infrared
Protostar Stage
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The initial contraction can span millions of years
The temperature of the nebula slowly rises until it is
hot enough to radiate energy from its surface
Protostar – a developing star not yet hot enough to
engage in nuclear fusion
When the core of a protostar has reached about 10
million K, pressure within is so great that nuclear
fusion of hydrogen begins, and a star is born
Heat from hydrogen fusion causes the gases to increase
their motion
Protostar
Protostars in the Horsehead
Nebula are circled
Concept Check
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What is a protostar?
A protostar is a developing star not yet hot
enough to engage in nuclear fusion.
Main-Sequence Stage
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Main-Sequence Stage – From the moment of birth
until the star’s death
The internal gas pressure struggles to offset the
unyielding force of gravity
Hydrogen fusion will last for a few billion years and
provides the outward pressure to keep the star from
collapsing
The more massive a main-sequence star, the shorter its
life span
A yellow star, like our sun, can remain in the mainsequence for approximately 10 billion years
Once the hydrogen fuel of the star’s core is depleted, it
evolves rapidly and dies
Main-Sequence Stage
Red-Giant Stage
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Occurs because the zone of hydrogen fusion
continually moves outward
When all the hydrogen is consumed, the core no longer
has outward pressure supporting it, and will contract
The core will grow hotter, the heat is radiated outward
and expands the surface
As the surface expands, it cools down, producing its
reddish color
The core will eventually reach a temperature which
allows Helium to Carbon fusion
Eventually all the fusion fuel will be consumed
The Sun will spend less than 1 billion years as a RedGiant
Red-Giant Stage
Globular Star Cluster, some of the oldest stars in the universe
Life Cycle of a Sun-like Star
Concept Check
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What causes a star to die?
A star runs out of fuel and collapses due to
gravity.
Burnout and Death
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We do not know that all stars, regardless of their size,
eventually run out of fuel and collapse due to gravity
Low Mass Stars – consume fuel at a slow rate, may
remain on main-sequence for up to 100 billion years,
end up collapsing into white dwarfs
Medium Mass Stars – go into red-giant stage, followed
by collapse to white dwarf by blowing out their outer
layer, and eventually light up planetary nebulae
Massive Stars – these have relatively short lifetimes, end
with a large supernova (brighter than the sun if near
Earth), this huge explosion blasts apart the star
Supernova – an exploding star that increases in
brightness many thousands of times
Possible Function of a Binary Pair
Planetary Nebula
Concept Check
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What is a supernova?
A supernova is the brilliant explosion that marks
the end of a massive star.
White Dwarfs
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White Dwarf – remains of low and medium
mass stars, extremely small stars with densities
greater than anything on Earth
The sun begins as a nebula, spends much of its
life as a main-sequence star, becomes a redgiant, planetary nebula, white dwarf, and finally,
black dwarf
White Dwarfs
Neutron Stars
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The smaller white dwarfs are actually a result of
the more massive stars
Neutron Stars – remnants of supernova events,
stars that are smaller and more massive than
white dwarfs
Electrons are forced to combine with protons to
form neutrons, because of how closely packed
the matter is
Neutron Stars
Supernovae
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The outer layer of a star is ejected, while the
core condenses to form a very hot neutron star
As the star collapses, it rotates faster, and it
generates very strong radio waves situated at its
magnetic poles creating pulses
Pulsar – a variable radio source of small size
that emits radio pulses in very regular periods
Supernovae
Black Holes
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Black Hole – A massive star that has collapsed
to such a small volume that its gravity prevents
the escape of everything, including light
How does astronomer find a black hole?
They look for material that is being
gravitationally swept up by a location that we
cannot see
Material that is swept in should be very hot and
emits large amounts of X-rays
Black Holes
Stellar Evolution
Assignment
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Read Chapter 25, Section 2 (pg. 707-714)
Do Chapter 25 Assessment #1-31 (pg. 725-726)