Our Evolving Universe-Origin of Elements-

by Yavuz EkşiEnka Schools

April 25th, 2007http://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 asbelonging 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

• formed a rotating disk

• condensed and collapsed due to gravity

• forming solar nebula – with an embryonic Sun – surrounded by a rotating cloud

• cloud of gases and dust

Milky Way: the Galaxy• A hazy

band of white light in the summer skies.

• Actually a myriad of stars.

Milky WayMilky way contains about 400 billion stars.

The Local Group

The Milky Wayis 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.

Large-Scale

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 CollidingGalaxies 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

p+

p+

Like electrical charges repel. So, protons in a gas avoid `collisions’

Hydrogen (proton) fusion

p+

p+

However, as a gas temperature goes up, the average speed of the particles goes up and the protons get closer before repelling oneanother. If the proton get very close, the short-range nuclear forcefuses them together.

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

H shell

He shell

C shell

Ne shell

O shell

Si shell

Fe core

• 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 CloudBefore 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 cloudsin the interstellar medium.

The solar system formed out of a gas cloud that had beeninjected with heavy elementsfrom many generations ofsupernova explosions.

Eagle Nebula

Our galaxy is not complete yet! It is rather an evolving systemin which new stars are bornand some stars die!

Star formation is an ongoing process in the Galaxy...

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

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)

Shorter wavelength (more blue)

For galaxies, we can use the doppler effect to measure velocity.

The Universe is Expanding

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!

… The universe is like a raisin bread!

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 21 3

-2 -1 10 2 3 4 65

Radio Raisin Moves at 3 m/s

Singing Raisin Moves

at 1 m/s

Distances Double in 1 sec

Raisins separated by

meters

Hubble’s law: v=H d

The EndThe notes are at

http://www.fizik.itu.edu.tr/eksiy/