Stellar Evolution

The Birth, Life, and Death of Stars

The Universe

• Everything– All matter,

space, and time

• The Universe is 13.72 billion years old

Cosmology

• The study of the origin of the Universe

The Sun• An average sized Star• About 4.5 billion years old

What is a Solar System?• A star and everything that revolves around it• Our Solar System is about ___ years old

A light-year

• A unit of distance, not time

• The distance light travels in one year

• 6 Trillion miles

Distance to Sun

• 93 million miles

• 8.3 light-minutes

Proxima Centauri

• The closest star to our sun

• About 4 light-years away

Galaxies

• Stars are not evenly distributed in space.

• They are in groups called Galaxies.

Types and Sizes of Galaxies• Types: Elliptical, Spiral, Irregular• Two sizes

– Giant– Dwarf

•

The Milky Way Galaxy

• 100,000 light years across• Has Hundreds of billions of stars

Galaxy Clusters

• A Group of Galaxies

• Local Group• 2 mly across• 3 large &

about 2 dozen dwarf

• Andromeda 2.2 mly

Galaxy Superclusters

• A cluster of clusters

• The Local (Virgo) Supercluster

• 100 clusters• 100 mly across

Nearest Superclusters

Galaxy Superclusters

The Visible Universe

How big is the Universe?

• The visible universe is 28 billion light years in diameter.

• Why is that all that is visible?

• The entire universe may be much bigger

How many Galaxies are there?• Hundreds

of billions• Each has

hundreds of billions of stars

Edwin Hubble

• 1920’s• Discovered

other galaxies• Discovered

the Universe is expanding

The Expanding Universe

• The Red Shift

• Doppler effect

The Doppler Effect

The Big Bang

• Tremendous explosion started the expansion of the universe

• All of the matter and energy of the universe was contained at one point

Characteristics of Stars

Star Properties and Classification

• Color• Temperature• Age• Apparent

brightness• Distance

from Earth

Star Brightness• Apparent Magnitude

– How bright it looks from Earth

• Absolute Magnitude– How much light it

actually produces

Apparent Magnitude (Brightness)

• Depends on actual brightness (luminosity) and distance away

Hertzsprung-Russell (H-R) Diagram

• Absolute Magnitude (Brightness

)

Compares a star’s Temperature (color) and its …

Hertzsprung-Russell (H-R) Diagram

Hertzsprung-Russell (H-R) Diagram

• Things to Know• Color depends on temperature

– Blue, White, Yellow, Orange, Red

• The higher the Temperature the Brighter the Star (if in the main sequence)– White Dwarfs and Red Giants are exceptions

• The Sun is in the main sequence (90% of stars)

Star Relative Size• The Sun is an averaged sized star

Stellar Evolution

The Formation and Life Cycle of Stars

Star Formation

• Originate in gas clouds in space called Nebula

• Mostly Hydrogen

• Gravity pulls it together

Nebula

• The contraction heats the gases

• When it gets hot enough (27 million degrees) nuclear fusion starts

Nuclear Fusion

• The reaction produce

s heat energy,

which causes

more fusion

• Hydrogen nuclei are fused to make helium

How big is a Nebula?

• The Orion Nebula is about 2.5 light years across

Old Age

• When the hydrogen runs low

• Contractions make more heat

• Causes nuclear fusion to make heavier elements

• Expansion results in a Red Giant

White Dwarf• When energy is used, it shrinks to make a white dwarf

Supernovas• Collapses abruptly

then explodes• Billions of times

brighter• Creates heavier

elements• Occurs only in very

massive stars

After a Supernova• The outer

layers are blasted into space to create a new nebula (starts the cycle over)

• The core collapses to form a neutron star

Neutron Star

• Left over after a supernova

• 1 teaspoon weighs billions of tons

Black Holes• A star

so dense, even light can not escape

Formation of Heavier Elements

• Elements heavier than hydrogen are formed by nuclear fusion in Stars

• Elements heavier then iron form during a Supernova

The End