Transcript 15. Our Star

The Fate of our Sun
&
The Origin of Atoms
Lecture 23
• The Death of our Sun and other Stars
• Nuclear Reactions creating new atoms
• The Big Bang: Origin of H and He
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Notes
• HW due Friday:
Read Chapter 14
Mastering Astronomy: Chapt 14
• No HW or Desc. Sections due next week (Thanksgiving)
• Next Week: Start Chapter 24: Life in the Universe
The Fate of our Sun
&
The Origin of Atoms
Lecture 23
• The Death of our Sun and other Stars
• The chemical enrichment of our Galaxy
• The Big Bang: Origin of H and He
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Chemical Composition of the Sun
Dark spectral lines are caused by
absorption of light by atoms
in the Sun’s atmosphere.
Magnesium
Calcium
Sodium
Iron
You can measure the amount of different atoms
from darkness of the absorption lines.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Composition of the Sun
(by Mass)
C, N, O, Ne, Fe, Others: 2%
He
28%
Hydrogen 70%
Abundances of atoms in the Sun is
representative of the universe as a whole:
Hydrogen and Helium Dominate.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
0.3%
0.2%
The Origin of the Atomic Elements
The 92 atomic elements were constructed by
nuclear reactions in the centers of stars - - -
All made in stars, except hydrogen, helium and lithium.
Tom Lehrer’s
The Elements
• http://www.youtube.com/watch?v=zGM-wSKFBpo
• http://www.youtube.com/watch?v=zGM-wSKFBpo
• Tom Lehrer singing it:
Missing Lawrencium. Listen for
• Berkelium and Californium
• http://www.youtube.com/watch?v=AcS3NOQnsQM
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Center of the Sun
Computer models (balancing gravity with pressure) show:
Temperature = 15 Million K
Collisions between atoms so violent:
• electrons removed from atoms: Atoms are Ionized
• leaving bare nucleus of each atom.
Nuclei of atoms collide & react
Nuclear Reactions
Fusion of Hydrogen to Helium
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Nuclear Fusion in the Sun:
Proton-Proton Chain
IN: 6 H, (2 e-)
OUT: He, 2 H, 2 e, 4 
4 H nuclei are converted into 1 He
nucleus and energy is released.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Luminosity of Sun:
Nuclear Burning of H to He
Mass Input: 4 p
Mass Output: 1 He (2p + 2n)
Look up Masses of particles:
Mass Input = 1.007 Mass Output
Mass is missing !
Converted to Energy:
E=
2
mc
Hydrogen is converted to Helium in Sun-like stars.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Death of the Sun
in 5 Billion Years
• Sun’s Core becomes pure helium!
• No Hydrogen burning possible.
• The Helium core begins to collapse.
– H shell (around Helium) heats up and H fusion begins there.
– Outer layers of the Sun expand.
– The Sun enters red-giant phase of its life.
Original Sun
Expanding:“Giant Star”
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Dying Sun: 5 billions years from now
Giant Star Phase
• The He core collapses until it heats to 108 K
– He fusion begins ( 3 He
•
C)
Carbon forms!
The star, called a Giant, is once again stable.
–
–
Gravity balanced by pressure, from He fusion reactions
Giant stars create, and release, most of the Carbon in the
universe: Key ingredient for organic molecules and life.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Fusion of 3 helium nuclei
into Carbon
“Triple-Alpha “
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Planetary Nebula
• When the Giant star exhausts its Helium fuel in the central core:
– the Carbon core collapses.
– Low & solar-mass stars don’t have enough gravitational energy to heat
to 6 x 108 K (temperature where Carbon fuses)
• The He & H burning shells produce huge amounts of energy.
• The energy blows away the star’s outer layers of gas:
• Making a “planetary nebula”.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Planetary Nebulae
Cat’s Eye Nebula
Twin Jet Nebula
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Planetary Nebulae
Ring Nebula
Hourglass Nebula
The collapsing Carbon core becomes a White Dwarf
© 2005 Pearson Education Inc., publishing as Addison-Wesley
When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
• C is exhausted, core
collapses until O fuses.
• The cycle repeats itself.
– O burns to Ne.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
• C is exhausted, core
collapses until O fuses.
• The cycle repeats itself.
– O burns to Ne.
– Ne burns to Mg.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
• C is exhausted, core
collapses until O fuses.
• The cycle repeats itself.
–
–
–
–
O burns to Ne.
Ne burns to Mg.
Mg burns to Si.
Si burns to Fe.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
When High Mass Stars Die:
Supergiants
They exhaust H fuel.
He C .
• They Contract, heat up to
600 million K.
– C fuses into O.
• C is exhausted, core
collapses until O fuses.
• The cycle repeats itself.
–
–
–
–
O burns to Ne.
Ne burns to Mg.
Mg burns to Si.
Si burns to Fe.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova
• The mass of the iron (Fe) core increases
- Iron can’t burn:
- No nuclear reactions: no energy production!
– Gravity overwhelms the gas pressure
– Star Collapses!
– Electrons are squeezed into protons  neutrons
•
The neutron core collapses until
abruptly stopped by neutrinos
flying outward!
– this takes only seconds
– The core recoils, bounces, and
neutrinos force the gas outward in
an explosion.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Core-Collapse
Supernova
Supernova
• The mass of the iron (Fe) core increases
- Iron can’t burn:
- No nuclear reactions: no energy production!
– Gravity overwhelms the gas pressure
– Electrons are
squeezed into protons  neutrons
•
The neutron core collapses until
abruptly stopped by neutrinos
flying outward!
– this takes only seconds
– The core recoils, bounces, and
neutrinos force the gas outward in
an explosion.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova Explosions
The explosion brings
temperature to
Billions of degrees:
The elements heavier
than Fe are instantly
created
Crab Nebula in Taurus
supernova exploded in 1054
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Four supernovae have
been observed in our
part of the Milky Way
Galaxy:
1006, 1054, 1572, &
1604
Supernovae
Tycho’s Supernova (X-rays)
exploded in 1572
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Veil Nebula
Supernova Remains
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova Remains
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova Remains
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova Remains
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Origin of the Atomic Elements
The 92 atomic elements were all
constructed in the centers of stars
(except hydrogen, helium and lithium).
The atoms that compose your
human body were made in
supernova explosions
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Supernova Explosion:
The first 0.15 seconds
Shock wave is created when the core of a massive star collapses to a proto-neutron star.
The shock does not immediately explode the star but "stalls" (because the
outer parts of the star [not shown in the movie] are exerting ram pressure on it). The shock
is "revived" within a tenth of a second from heating by neutrinos emitted
from the proto-neutron star. The different colors correspond to gas of different temperature.
Core-Collapse Supernova Explosion
The Origin of the Atomic Elements
The 92 atomic elements were all
constructed in the centers of stars
(except hydrogen, helium and lithium).
The atoms that compose your
human body were made in
supernova explosions
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Origin of the Atomic Elements
The 92 atomic elements were all
constructed in the centers of stars
(except hydrogen, helium and lithium).
Where did all the
Hydrogen and Helium
Come from?
© 2005 Pearson Education Inc., publishing as Addison-Wesley
•
•
•
•
•
Explosion: Hot and Dense. Over a trillion degrees.
Time and Space Created.
Universe expands ever since. Accelerating now.
Science can not describe what happened
13.5 Billion Years Ago.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
before the Big Bang.
Depiction of Big Bang
t < 0.001 sec
• Quarks and Electrons as numerous as photons.
(No Protons or neutrons: At billions of
degrees,any protons collide, break apart into
quarks.)
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Quarks and Photons Annihilate:
Equilibrium
© 2005 Pearson Education Inc., publishing as Addison-Wesley
t < 0.001 sec
• Quarks and Electrons as numerous as photons.
• Time > 0.001 sec:
Quarks combined to form protons & neutrons
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Protons and Neutrons
Are Composed of 3 Quarks
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Era of Nucleosynthesis
(t < 3 min)
• Protons & neutrons fuse !
4p
He
• Some He nuclei torn apart by the high temperatures
9
• When Universe was 3 min old, it had cooled to 10 K.
• At this point, the fusion stopped
• Afterwards, the matter in the Universe was:
• 70% Hydrogen nuclei (i.e. individual protons)
• 25% Helium nuclei
• trace amounts of Deuterium (H isotope) & Lithium nuclei
© 2005 Pearson Education Inc., publishing as Addison-Wesley
© 2005 Pearson Education Inc., publishing as Addison-Wesley
History of the Universe
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Universe since the Big Bang: Gravitational Attraction of material
Billions of years ago
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Universe since the Big Bang: Gravitational Attraction of material
Billions
ofInc.,
years
ago as Addison-Wesley
© 2005 Pearson
Education
publishing
Era of Galaxies ( t >
9
10
yr)
• The first galaxies came into existence about 1 billion
years after the Big Bang.
• This is the current era of the Universe.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Lecture 22
The Fate of the Sun
&
The Origin of Atoms
End of Lecture 22
© 2005 Pearson Education Inc., publishing as Addison-Wesley