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Our Evolving Universe
-Origin of Elements-
by Yavuz Ekşi
Enka Schools
April 25th, 2007
http://www.fizik.itu.edu.tr/eksiy/
The Planets
MNEMONIC: My Very Educated Mother Just Sent Us Nine Pizzas
With the exception of Pluto each of the planets can be thought of as
belonging to one of two distinct groups: terrestrial or Jovian
Imagening the distances
• Imagine the Solar System being a soccer ground
(about 100 m long).
• The Sun would be a glaring orange in the centre.
• Pluto would encircle the sun at the edge of the
soccer ground, having the size of a dust
particle.
• The Earth would be 1,30m away from the
“orange“, having the size of a sesame seed.
Origin of Our Solar System
Solar nebula theory
• cloud of gases and dust
• formed a rotating
disk
• condensed and
collapsed due to
gravity
• forming solar nebula
– with an embryonic Sun
– surrounded by a rotating cloud
Milky Way: the Galaxy
• A hazy
band of
white light
in the
summer
skies.
• Actually a
myriad of
stars.
Milky Way
Milky way contains about 400 billion stars.
The
Local
Group
The Milky Way
is a member
of a group of
galaxies called
the Local Group
Our Neighbour Galaxy: Andromeda (M31)
2.5 million ly away (just 25 times the diameter of our galaxy).
Contains about one trillion stars.
Downtown: The Virgo Super
Cluster: 50 m.l.y
The
Coma
Cluster
350 m.l.y.
LargeScale
Structure
of the
Universe
to 500
m.l.y.
Stars in the Milky Way do not
collide
• The radius of the Sun is 700.000 km
(about 2 light seconds)
• The closest star other than the Sun is
about 4 light years away.
• Mean separation between the stars is
much greater than the mean diameters of
the stars (approx. 50 million times).
• It is very unlikely that two stars moving in
the galaxy collide.
Galaxies Colliding
Galaxies do collide
because mean separation
is not much larger than the
typical diameter of a galaxy.
Where does the elements come from?
• Only hydrogen and helium was created
in the Big Bang.
• We have Carbon, Nitrogen, Oxygen, and
iron in our body.
• Where does these elements come from?
Four Forces of Nature
•
•
•
•
Gravity
Electromagnetism
Strong interaction (short range)
Weak nuclear interaction (short range)
Hydrogen (proton) fusion
Like electrical charges repel. So, protons in a gas
avoid `collisions’
p+
p+
Hydrogen (proton) fusion
However, as a gas temperature goes up, the average speed of the
particles goes up and the protons get closer before repelling one
another. If the proton get very close, the short-range nuclear force
fuses them together.
p+
p+
Stellar Evolution
• Heavy elements are formed in stars
during their evolution.
• Thermonuclear reactions produce
elements up to iron.
• All fusion reactions before iron are
exotermic.
• After iron, endothermic.
Onion Skin Model
C shell
Ne shell
H shell
He shell
O shell
Fe core
Si shell
• But how did these elements came into our
body?
• What happens to a star after it exhausts all
matter?
• The core collapses and the outer layers of
the star are expelled in a gigantic
explosion.
Supernova 1987a in the Large Magellanic Cloud
Before
After
Crab Nebula Supernova Remnant
With Supernova Explosions…
• The outer layers of the stars are expelled
into the interstellar medium.
• Even higher elements like gold, uranium
etc are formed during the SN explosion.
• Now the interstellar medium is richer with
heavy elements.
• …but how did these elements in the
interstellar medium came to our body?
Horsehead Nebula
Stars form from gas clouds
in the interstellar medium.
The solar system formed out
of a gas cloud that had been
injected with heavy elements
from many generations of
supernova explosions.
Eagle Nebula
Star formation is an ongoing
process in the Galaxy...
Our galaxy is not complete yet!
It is rather an evolving system
in which new stars are born
and some stars die!
The Cycle of Matter
Not all stars end with a
supernova explosion
• The Sun will not die with a SN
explosion.
• All stars with mass smaller than 1.4
solar masses at the end of their life will
end with a much less energetic explosion
called a planetary nebula.
• Such objects will form white dwarfs.
The “Helix” Planetary Nebula in Aquarius
Inside stellar remnants
Aristoteles: The celestial objects
are made up of a separate
element called ether.
Modern Science: Celestial
objects are made of the same
stuff that the Earth is made up of.
...because the Earth itself is a
celestial object!
All celestial objects are
subject to change. The Earth
is a celestial object and so it
must be changing.
August 17, 1999
The Lands are moving!
The Earth is not complete yet!
• The lands, insensitive to our presense,
continue their motion that they started
millions of years ago.
• The Earth is not a complete place but
rather an evolving celestial object.
The Universe Expanding
Doppler Effect
The first crest travels out in
circle from the original position
of the plane
Shorter wavelength
(more blue)
At a later time, a second
crest is emitted from the
planes new position,
but the old crest keeps
moving out in a circle
from the planes original
position
The same thing happens again at
a later time
Longer
wavelength
(more red)
For galaxies, we can use the doppler effect to
measure velocity.
The Universe is Expanding
… The universe is like a raisin bread!
Expansion of the Universe
– All galaxies are moving away from us
– More distant galaxies moving away faster
Raisins move with
dough, not through it.
Galaxies move with
space, not through it!
Expansion is observed to be the same
in all galaxies
What DO we know?
– All galaxies are moving away from us
– More distant galaxies moving away faster
-1
0
1
2
Raisins
separated by
meters
3
Distances
Double in 1 sec
Singing
Raisin
Moves
at 1 m/s
-2
-1
Radio Raisin
Moves at 3 m/s
0
1
2
3
4
5
6
Hubble’s law: v=H d
The End
The notes are at
http://www.fizik.itu.edu.tr/eksiy/