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