Foundations of Earth Science
Digi
chapter16-lecture-powerpoints-BeyondOurSolarSystem.pptx
Beyond Our Solar System
Chapter 16 Lecture
Natalie Bursztyn
Utah State University
Foundations of Earth Science
Eighth Edition
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Define cosmology.
Describe Edwin Hubble’s most significant discovery about the universe.
Focus Questions 16.1
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Cosmology
Study of the Universe
Light-year
Distance light travels in one year
Slightly less than 10 trillion km
The Universe is ~13.8 billion years old
The Universe
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The Universe
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The Universe
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The Universe
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Define main-sequence star.
Explain the criteria used to classify stars as giants.
Focus Questions 16.2
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Hertzsprung-Russell Diagram
Shows the relation between stellar brightness (absolute magnitude) and temperature
Diagram is made by plotting each star’s:
Luminosity (brightness) and
Temperature
Classifying Stars: H-R Diagrams
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Parts of an H-R diagram
Main-sequence stars
90% of all stars
Band through the center of the H-R diagram
Sun is in the main-sequence
Giants (or red giants)
Large and very luminous
Upper-right on the H-R diagram
Very large giants are called supergiants
Only a few percent of all stars
Classifying Stars: H-R Diagrams
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White dwarfs
Fainter than main-sequence stars
Small (approximate the size of Earth)
Lower-central area on the H-R diagram
Not all are white
Classifying Stars: H-R Diagrams
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Classifying Stars: H-R Diagrams
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List and describe the stages in the evolution of a typical Sun-like star.
Focus Question 16.3
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Stars exist because of gravity
Two opposing forces in a star are:
Gravity: contracts
Thermal nuclear energy: expands
Stages
Birth
In dark, cool, interstellar clouds (nebulae)
Gravity contracts the cloud
Temperature rises
Becomes a protostar
Stellar Evolution
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Protostar
Gravitational contraction of gasses continues
Core reaches 10 million K
Hydrogen nuclei fuse
Become helium nuclei
Process is called hydrogen fusion
Energy is released
Outward pressure balanced by gravity
Star becomes a stable main-sequence star
Stellar Evolution
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Main-sequence stage
Stars age at different rates
Massive stars
Use fuel faster
Exist for only a few million years
Small stars
Use fuel slowly
Exist for perhaps hundreds of billions of years
90% of a star’s life is in the main-sequence
Stellar Evolution
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Red giant stage
Hydrogen burning migrates outward
Star’s outer envelope expands
Surface cools
Surface becomes red
Core collapses as helium converts to carbon
Eventually all nuclear fuel is used
Gravity squeezes the star
Variable stars alternately expand and contract
Never reach equilibrium
Stellar Evolution
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Stellar Evolution
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Burnout and death
Final stage depends on mass
Low-mass star
0.5 solar mass
Red giant collapses and becomes a white dwarf
Intermediate-mass (Sun-like) star
Between 0.5 and 8 solar masses
Red giant collapses, planetary nebula forms, then becomes a white dwarf
Massive star
Over 8 solar masses
Terminates in a supernova
Interior condenses and may produce a hot, dense object that is either a neutron star or a black hole
Stellar Evolution
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Stellar Evolution
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Compare and contrast the final state of Sun-like stars to the remnants of the most massive stars.
Focus Question 16.4
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White dwarves
Small (some no larger than Earth)
Dense
Can be more massive than the Sun
Spoonful weighs several tons
Atoms take up less space
Electrons displaced inward
Called degenerate matter
Hot surface
Cools to become a black dwarf
Stellar Remnants
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Stellar Remnants
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Neutron stars
Forms from a more massive star
Star has more gravity
Squeezes itself smaller
Remnant of a supernova
Gravitational force collapses atoms
Electrons combine with protons to produce neutrons
Small size
Stellar Remnants
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Neutron stars
Pea size sample
Weighs 100 million tons
Same density as an atomic nucleus
Strong magnetic field
First one discovered in early 1970s
Pulsar (pulsating radio source)
Found in the Crab Nebula (remnant of an a.d. 1054 supernova)
Stellar Remnants
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Stellar Remnants
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Black holes
More dense than neutron stars
Intense surface gravity lets no light escape
As matter is pulled in
Becomes very hot
Emits x-rays
Cygnus X-1
First black hole to be identified
Orbits a massive supergiant companion once every 5.6 days
Accretion disk—gases spiral around a “void” while emitting a steady stream of x-rays
Stellar Remnants
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Stellar Remnants
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List the three major types of galaxies.
Explain the formation of large elliptical galaxies.
Focus Questions 16.5
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Galaxies—collections of interstellar matter, stars, and stellar remnants that are gravitationally bound
Three basic types of galaxies
Spiral galaxy
Arms extending from nucleus
Large diameter of 20,000 to 125,000 light years
Contains both young and old stars
e.g., Milky Way
Barred spiral galaxy – band of stars extending outward from central bulge merges with spiral arms
Galaxies and Galactic Clusters
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Galaxies and Galactic Clusters
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Galaxies and Galactic Clusters
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Elliptical galaxy
Ellipsoidal shape
Most are smaller than spiral galaxies; however, they are also the largest known galaxies
All small galaxies are known as dwarf galaxies
Irregular galaxy
Lacks symmetry
About 25% of all galaxies
Contains mostly young stars
For example, Magellanic Clouds
Galaxies and Galactic Clusters
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Galaxies and Galactic Clusters
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Galactic cluster
Group of galaxies
Some contain thousands of galaxies
Local Group
Our own group of galaxies
Consists of more than 40 galaxies
May contain many undiscovered dwarf galaxies
Supercluster
Huge swarm of galaxies
May be the largest entity in the universe
Galaxies and Galactic Clusters
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Galaxies and Galactic Clusters
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Galactic Collisions
Driven by one galaxy’s gravity disturbing another
A large galaxy may engulf a dwarf satellite galaxy
Two dwarf satellite galaxies are currently merging with the Milky Way
Two galaxies of similar size may pass through one another without merging
Interstellar matter will likely interact
Triggers an intense period of star formation
In 2 to 4 billion years, 50% probability that Milky Way and Andromeda Galaxies will collide and merge
Galaxies and Galactic Clusters
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Galaxies and Galactic Clusters
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Describe the big bang theory.
Explain what it tells us about the universe.
Focus Questions 16.6
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Big Bang Theory
Describes the birth, evolution, and fate of the universe
Universe was once confined to a “ball” that was:
Supermassive
Dense
Hot
About 13.8 billion years ago, universe began expanding rapidly in all directions
The Big Bang Theory
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Doppler effect
Change in wavelength due to motion
Movement away stretches the wavelength
Longer wavelength
Light appears redder
Movement toward “squeezes” the wavelength
Shorter wavelength
Light shifted toward the blue
The Big Bang Theory
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The Big Bang Theory
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Most galaxies exhibit a red Doppler shift (cosmological red shifts)
Far galaxies
Exhibit the greatest shift
Greater velocity
Discovered in 1929 by Edwin Hubble
Hubble’s Law
Recessional speed of galaxies is proportional to their distance
Expanding universe accounts for red shifts
The Big Bang Theory
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The Big Bang Theory
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Predictions of the Big Bang Theory
If the universe is unimaginably hot, then researchers should be able to detect the remnant of that heat
Continued expansion of the universe would stretch the waves so by now they are detectable as long-wavelength radio waves
Cosmic background radiation
Detected in 1965
The Big Bang Theory
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Fate of the universe
Two possibilities:
“Big chill”
Stars slowly burn out
Replaced by invisible degenerate matter and black holes
Travel outwards through an endless, dark, cold universe
“Big crunch”
Outward flight of galaxies slows and eventually stops
Gravitational contraction causes all matter to collide and coalesce into high-energy, high-density state, from which the universe began
The Big Bang Theory
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The Big Bang Theory
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Final fate depends on density of the universe
If density is more than the critical density, universe will contract
If density is less than the critical density, universe will expand forever
The Big Bang Theory
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Two other constituents complicate the fate of the universe:
Dark matter
One quarter of the universe
Produces no detectable light energy
Exerts a force much like gravity
Dark energy
Exerts a force that pushes matter outward
Though to be the dominant force in behind the fate of the universe
Predicts universe will expand forever
The Big Bang Theory
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