Chapter 10The 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:• • 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.

• • 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.

• • 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

• Twinkle Twinkle Little Star• How I wonder what you are• Up above the world so high• Like a diamond in the sky

Michele Owens

StarsThey are prettyThey are brightAnd I see them In the night

TS Eliot The Hollow Man

• 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 razorbladeinto a mountainrange;lenses extend

unwish through curving wherewhen until unwishreturns on its unself.A world of madeis not a world of born-pity poor flesh

and trees, poor stars and stones, but never thisfine specimen of hypermagical

ultraomnipotence. We doctors know

a hopeless case if-listen:there's a hellof a good universe next door;let's go

Chapter 10 Overview

• 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)

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+

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H-1

He-3

H-2

+Energ

y

Energy

Hydrogen Fusion

• 4 H1 He4 + energy +neutrinos

Nuclear FusionHelium Nuclei

+

+

++Energ

y

Energy

+

++

++

Helium Fusion

• 4He + 4He + 4He 12C + γ (gamma ray energy)• 12C + 4He 16O + γ

Fusion SummaryIn 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

• 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 cake-

just when you thought it was out, it lights again.

Chandrasekhar Limit

• 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 StarsRead 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 HolesRead Page 332, Questions 44-46

• 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• 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

• 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.