Chapter 10
The Deaths of Stars
Reflective Essay 4/2/2014
• Each student will write a reflective essay of 500 to 1000 words on a topic
selected from the following list:
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• 1. How has the study of astronomy affected your search for meaning and
purpose in life? This could include how this study has impacted your
religious and philosophical views. This could either be a personal
reflection or a general reflection of how the study of astronomy might
impact someone’s religious and philosophical views.
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• 2. Astronomy is considered an essential part of a classical education. How
has what you have learned in astronomy reinforced, contradicted,
complimented, or completed other courses you have taken.
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• 3. Debate the question, should billions of dollars of public funds be spent
for astronomical research? Pick a side and argue for or against spending
public funds for astronomy research.
Twinkle Twinkle
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Twinkle Twinkle Little Star
How I wonder what you are
Up above the world so high
Like a diamond in the sky
Michele Owens
Stars
They are pretty
They are bright
And I see them
In the night
TS Eliot The Hollow Man
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This is the way the world ends
This is the way the world ends
This is the way the world ends
Not with a bang but a whimper.
pity this busy monster,manunkind...
(XIV) by E. E. Cummings
• pity this busy monster,manunkind,
not. Progress is a comfortable disease:
your victum(death and life safely beyond)
plays with the bigness of his littleness
-electrons deify one razorblade
into a mountainrange;lenses extend
unwish through curving wherewhen until unwish
returns on its unself.
A world of made
is not a world of born-pity poor flesh
and trees, poor stars and stones, but never this
fine specimen of hypermagical
ultraomnipotence. We doctors know
a hopeless case if-listen:there's a hell
of a good universe next door;let's go
Chapter 10 Overview
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Low Mass Stars and Planetary Nebulae
Low Mass Stars and Nova
High Mass Stars and Type II Supernovae
Neutron Stars, Pulsars and Gamma Ray Bursts
Black Holes
– Relativity Theories
Typical Nucleus
• Electrical force pushes apart
• Strong Nuclear force holds together
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Nuclear Fusion (P553)
H-1
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Energy
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H-2
He-3
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Energy
Hydrogen Fusion
• 4 H1  He4 + energy +neutrinos
Nuclear Fusion
Helium Nuclei
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Energy
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Energy
Helium Fusion
• 4He + 4He + 4He  12C + γ (gamma ray energy)
• 12C + 4He  16O + γ
Fusion Summary
In a Massive Star
Temperature
Element Fused Elements Formed
Time
4 X 107 K
Hydrogen
helium
7 x 106 yrs
2 x 108 K
Helium
Carbon and oxygen
5 x 105 yrs
6 X 108 K
Carbon
Neon and magnesium
600 yrs
1.2 X 109 K
Neon
Oxygen & magnesium
1 yr
1.5 X 109 K
Oxygen
Sulfur, silicon, phosphorus
6 months
2.7 X 109 K
Silicon
Iron
1 day
Supernova
explosion
Heavy elements
hours
White Dwarf
Collisions
Heavier Elements
Leaving the Main Sequence
• Stars join the main sequence when they begin
hydrogen fusion in their cores. They leave the
main sequence and become giant stars when
the core hydrogen is depleted.
• Red giants experience significant mass loss
because of large surface areas and low gravity.
• Detect the mass moving out from these stars
with Doppler shift of spectra lines.
Really Low Mass Stars
• < 0.4 Solar Masses Page 310
– Convert all hydrogen to helium
– 100’s of Billions of years
– Red Dwarfs
– 85% of Milky Way Stars
– Stop fusing (none have yet stopped)
– Cool Off
– Move down and to the right
Low Mass Stars (a little bigger)
• 0.4 to 8 Solar Masses P310
– Hydrogen fusion in the core ceases
– Hydrogen fusion continues in a shell around the
core.
– Core cools and contracts causing core
temperature to rise again
– Core temperature reaches 100 million K
– Increased heat causes star to expand
– Helium Fusion begins in the core
Helium Fusion
• Hydrogen fusing shell surrounds a small compact
core of almost pure helium
• Hydrogen fusion in the shell adds helium to core
which contracts more and heats up more.
• 108 K Helium fusion begins
• 4He + 4He 8Be + 4He  12C + γ + 4He  16O + γ
• Hydrogen fusion continues in a shell around the
core.
• Core Helium fusion last a relatively short time
• 100 million years
2nd time around
• When Helium fusion begins, the new energy
pushes the outer layer of the star out
increasing its size and therefore its brightness.
• Helium fusion produces oxygen and carbon.
• The star moves up and to the right of the H-R
diagram becoming a low temperature red
super giant.
Late Phases of Low Mass Stars
• Outer layers of these stars expand and
thereby cool.
• Pressure inside increases and pushes more
and more material into space around the star.
• Eventually enough outer material is ejected
that the core becomes visible.
• Planetary Nebula- ejected material
• Core becomes a White Dwarf
Future of Our Sun
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7 billion years from now
Hydrogen fusion in the core will cease
Core will contract but outside will expand
Diameter of 1 AU
100 times present size
Surface Temperature drop to 3500 K
Brightness 2000 X current
Destroy inner planets and vaporize gases of gas
giants
Figure 10-2 Page 311
Read
• Read page 310 and 311 and complete
questions 1-9 of the study guide.
Nova
• A White Dwarf in a Binary System
• Close enough to another ordinary star to
attract material from the other star.
• Added material compresses, the temperature
rises until hydrogen fusion begins again.
• Blows outer layers into space.
• Kind of like a trick candle on a birthday cakejust when you thought it was out, it lights
again.
Chandrasekhar Limit
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1930’s Indian student sailing to England
Worked out the theory
Page 315
Over weight white dwarf
Electron degeneracy
White dwarf > 1.4 solar masses is unstable
and will implode
Read Page 315
• Read Page 325-316
• Answer questions 18-25
Type Ia Supernova (P315)
• A White Dwarf in a Binary System
• Close enough to a giant star to attract material
from the other star.
• Added material makes the star >1.4 solar masses
• Added material increases pressure deep inside
the carbon core enables carbon fusion.
• No outer layer to absorb the energy.
• Core explodes (not just a layer on the outside)
• Nuclear Explosion
Type Ia Supernova
• Lack hydrogen spectral lines because the star had
already shed outer layers of gas.
• All the stars experiencing Supernova are >1.4 solar
masses.
• All have the same peak magnitude (Luminosity)
• Because they all peak at the same absolute
magnitude, they can be used to determine distance.
• Know absolute magnitude, observe its apparent
magnitude, calculate distance.
Read Pages 316-Section 10-5
• Answer questions 26-32
Mass > 8 Solar Masses (page 316)
• When helium fusion ends• Gravitational compression collapses the
carbon and oxygen core driving the
temperature above 600 million K
• Carbon fuses and produces neon and
magnesium.
• Given sufficient mass the processes repeat at
ever increasing temperatures forming ever
more massive elements. Up to iron
Fusion Summary (P316)
Temperature
Element Fused Elements Formed
Time
4 X 107 K
Hydrogen
helium
7 x 106 yrs
2 x 108 K
Helium
Carbon and oxygen
5 x 105 yrs
6 X 108 K
Carbon
Neon and magnesium
600 yrs
1.2 X 109 K
Neon
Oxygen & magnesium
1 yr
1.5 X 109 K
Oxygen
Sulfur, silicon, phosphorus
6 months
2.7 X 109 K
Silicon
Iron
1 day
Supernova
explosion
Heavy elements
hours
White Dwarf
Collisions
Heavier Elements
Nucleosynthesis- the process of converting
lower-mass elements into higher mass ones.
Fusing Higher Mass Nuclei
• Given sufficient temperature elements up to
iron will fuse.
• Iron and elements with higher atomic number
do not produce as much energy in fusion as
required to start fusion.
• Fusion is not sustained.
• These higher atomic number elements are
produced in the final explosion of stars.
Multiple Layer Giant Stars
Read Page 317, Questions 33-41
• Iron Core – no fusion
• Iron deposited into the core exceeds Chandrasekhar
limit
• Core Collapses
• Tears the star apart in a few seconds.
• Breaks atoms in the core into protons, electrons
and neutrons
• Produce neutrinos
Type II Supernova
• Tremendous energy of the neutrinos collapses
the core
• Core collapses under the pressure
• Core rebounds (core bounce)
• Shockwave blasts the outer layers into space
• Star becomes a Type II Supernova
• Fusion of heavier elements occur in the
explosion.
• We are made of star dust
Gum Nebula Supernova Remnants
Cassiopeia Supernova Remnants
Neutron Stars
• Read Page 323, Questions 42,43
• Core recontracts
• Forcing electrons and protons together forming
neutrons
• The core is then a Neutron Star
• 1 teaspoon would weigh 1 billion tons on earth.
• 1 teaspoon of white dwarf would weigh only 5
tons on earth.
Black Holes
Read Page 332, Questions 44-46
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Stellar remnants > 3 solar masses
Not a star but what is left over from the star
Gravitation ‘wins” the battle,
The object collapses on itself.
Its gravitational attraction becomes so strong
that nothing- not even light- can escape
• Black Hole
Pulsars
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Jocelyn Bell 1968, Cambridge University
Radio telescope detected regular pulses
Period 1.337301seconds
LGM1 (Little Green Men 1)
Others detected with periods of .2 s to 1.5s
Discovered pulsar in the crab nebula the
remnant of the ancient Chinese Supernova
Various Theories
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Alien civilization communicating
Contracting and expanding
Rotating pairs
Finally
Magnetic Field of Rotating Neutron Stars
When star shrinks to form the Neutron Star
the magnetic field is compressed and
strengthened.
Light House Model
Einstein 1905 (P332)
Theory of Special Relativity
• Newtonian Relativity (Galileo)
– Two cars moving toward each other at 50mph will
approach each other at 100mph
• Einstein’s Two Assumptions
– Your description of physical reality is the same
regardless of the (constant) velocity at which you
are moving.
– Regardless of your speed or direction, you always
measure the speed of light to be the same.
Newton’s “Laws”
• Accurate only for objects with relatively small
masses, slow velocities compared to the
speed of light, and low densities.
• Objects on earth
• Apply only to motion sufficiently far from
large masses or high-density. (Sun)
• Apply to projectile motion on Earth, to the
motion of planets around the Sun but not to
Mercury.
Stationary Observer
Relativity
• Newtonian
• to the person in the car the light would appear to
travel at “1.5c”
• Special Relativity
• to the person in the car, the light appears to
travel at “c”
• to the person on the ground the light would
appear yellow
• to the person in the car, the light would appear
green. Doppler effect- blue shift
Other Results of Special Relativity
• The length of an object (as observed from
“rest”) decreases in the direction of its motion
as its speed increases. Length contraction
• Clocks that you see as moving run more slowly
than do clocks at rest. Biological processes
slow down. Time dilation
• Space and time cannot be considered as two
separate concepts spacetime
• The mass of an object increases as it moves
faster. At speed of light– infinite mass
• Infinite mass impossible so speed of light is
max speed possible
General Relativity 1915
• Special because assumes constant velocity,
does not apply to accelerating systems or
systems under the influence of gravity.
• Spacetime changes shape in the presence of
matter.
• Greater the mass the more distortion or
curvature.
• Curvature of spacetime creats attraction
between all pieces of matter- gravitational
force.
History of Gravity
• Aristotle – 4 types of matter, each type seeks
it own place
– Earth naturally moves toward the center of earth
• Galileo- all objects fall at the same rate
• Newton – force between every object in the
universe proportional to the product of the
masses and inversely proportion to the square
of the distance between them.
• Einstein – gravitation attraction due to
curvature of spacetime in the presence of
mass.
Spacetime affects on light
• Curvature of spacetime changes the path and
wavelength of light that passes near any matter.
• Imagine flying in an airplane between two cities –
don’t fly in a straight line but a curved line –
geodesic
• Photons that leave the vicinity of a star lose
energy in climbing out of the star’s gravitational
field. They don’t slow down but they increase
wavelength
• Gravitational redshift
Confirmation of General Relativity
• Light is measurably deflected by the curving of
space due to the presence of matter like stars
or entire galaxies.
• Einstein Predicted the angle of deflection.
• Expedition to Turkey to observe and measure
this deflection during a solar eclipse.
• WW I broke out and the astronomer was
captured by the Turks.
More Observational Evidence
• The perihelion (farthest from sun) position of
Mercury as seen from the Sun shifts or
precesses by 43 arcsec per year more than
predicted by Newtonian gravitational theory.
• The orbits of stars in binary systems follow
paths predicted by Einstein rather than by
Newton.
More Evidence
• Spectra of stars are observed to have
gravitational redshifts predicted by GR
• Observe a spectra line and note how much it
is shifted to the red.
Near a Neutron Star
• Neutron stars mass sufficiently dense to warp
the space around itself
• Photons flying outward at an angle arc back
inward.
• Photons flying straight upward are redshifted
by “gravity” (warping of spacetime)
Black Holes
• In the constant battle between
– Thermal Pressure
– Gravitational Attraction
• Gravity “Wins”
• The object collapses on itself becoming
unbelievably dense (large mass in small
volume)
• Gravitational attraction so great not even light
can escape.
• Not sucking everything in the universe into it.
Black Hole
• Black holes are formed by the collapse of a
neutron star which makes it even denser
• Matter compressed to infinite density – called
a singularity
• Not a hole at all…
GR predicts black holes
• For a black hole, no light escapes.
• Light leaving at an angle is deflected back into
the black hole.
• Light straight up is infinitely redshifted and
thereby disappears.
Formation of Black Hole
• Stellar remnant (neutron star) collapses to
infinite density (huge mass, zero volume).
• Loses it’s magnetic field
• Energy radiates away in gravitational radiation
• Gravitational wave travels as ripples in the
fabric of spacetime.
• Astronomers are building “gravitation wave”
detectors.
• Indirectly observed in binary star systems
Structure of Black Hole
• Event horizon spherical separation between
black hole and the rest of the universe.
• Singularity the infinitely dense matter at the
center of a BH
• Schwarzschild radius RSch distance from center
of BH to the event horizon.
Types of Black Holes
• Properties of a BH
– mass
– angular momentum
– charge ???
• Spinning thousands of times per second
• Ergoregions donut shaped space outside EH
Schwarzschild black hole
Kerr black hole
Ergoregion
• An object cannot remain at rest in this region
• If moving fast enough an object can fly out of
the region.
• Below a minimum speed the object falls into
the BH.
• Not sucking everything in the universe into it.
Results of Special Relativity
• The length of an object (as observed from
“rest”) decreases in the direction of its motion
as its speed increases. Length contraction
• Clocks that you see as moving run more slowly
than do clocks at rest. Biological processes
slow down. Time dilation
• Space and time cannot be considered as two
separate concepts spacetime
• The mass of an object increases as it moves
faster. At speed of light– infinite mass
• Infinite mass impossible so speed of light is
max speed possible
Bizarre Happenings at Event Horizon
• Imagine a blue probe descending toward the BH
• 100 Schwarzschild radii
• Clock on probe slows down as observed from
outside the probe
• Side of the probe toward the BH stretches
• Violent elongation and thinning
• Appearance of probe changes toward the red
• Appear to an outside observer as hovering
• Disintegrates as it falls inward.
Evidence for Black Holes
• Observed by their effects on the orbits of
other stars and on gas and dust near them.
• Often found in binary star systems
– Because the extra mass to produce the BH comes
from the other star
• Pressure and heat forms x-rays which can be
detected.
Types of Black Holes
• Stellar Black Holes formed by the collapse of
neutron stars.
• Super Massive Black Holes formed by the
collision and merger of stellar black holes
– Centers of Galaxies
• Tiny Blackholes - theorized but not observed
Wormholes
• Science fiction concept of traveling great
distances quickly or to other dimensions are
just fiction.
• Calculations indicate that an object could not
survive passage through a BH even if there
were a way to “come out somewhere”
• General Relativity predicts that a black hole
could connect to another part of spacetime or
even some other universe.
• Astrophysicist are skeptical
GR Insufficient
• Black holes are formed by the collapse of a
neutron star.
• Matter compressed to infinite density – called
a singularity
• Not a hole at all…
• General relativity and quantum mechanics do
not explain the state of matter in a black
holes’ singularity
• Superstrings theory.