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Earth Science, 12e. Beyond Our Solar System Chapter 22. After reading, studying, and discussing the chapter, students should be able to : Discuss the principle of parallax and explain how it is used to measure the distance to a star.

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earth science 12e

Earth Science, 12e

Beyond Our

Solar SystemChapter 22


After reading, studying, and discussing the chapter, students should be able to:

  • Discuss the principle of parallax and explain how it is used to measure the distance to a star.
  • List and describe the major intrinsic properties of stars.
  • Describe the different types of nebulae.
  • Describe the most plausible model for stellar evolution and list the stages in the life cycle of a star.
  • Describe the possible final states that a star may assume after it consumes its nuclear fuel and collapses.
  • List and describe the major types of galaxies.
  • Describe the big bang theory of the origin of the universe.

Learning Objectives

properties of stars
Properties of stars
  • Distance
    • Measuring a star’s distance can be very difficult
    • Stellar parallax
      • Used for measuring distance to a star
      • Apparent shift in a star’s position due to the orbital motion of Earth
      • Measured as an angle
      • Near stars have the largest parallax
      • Largest parallax is less than one second of arc
properties of stars1
Properties of stars
  • Distance
    • Distances to the stars are very large
    • Units of measurement
      • Kilometers or astronomical units are too cumbersome to use
      • Light-year is used most often
        • Distance that light travels in 1 year
        • One light-year is 9.5 trillion km (5.8 trillion miles)
    • Other methods for measuring distance are also used
properties of stars2
Properties of stars
  • Stellar brightness
    • Controlled by three factors
      • Size
      • Temperature
      • Distance
    • Magnitude
      • Measure of a star’s brightness
properties of stars3
Properties of stars
  • Stellar brightness
    • Magnitude
      • Two types of measurement
        • Apparent magnitude
          • Brightness when a star is viewed from Earth
          • Decreases with distance
          • Numbers are used to designate magnitudes – dim stars have large numbers and negative numbers are also used
properties of stars4
Properties of stars
  • Stellar brightness
    • Magnitude
      • Two types of measurement
        • Absolute magnitude
          • “True” or intrinsic brightness of a star
          • Brightness at a standard distance of 32.6 light-years
          • Most stars’ absolute magnitudes are between –5 and +15
properties of stars5
Properties of stars
  • Color and temperature
    • Hot star
      • Temperature above 30,000 K
      • Emits short-wavelength light
      • Appears blue
    • Cool star
      • Temperature less than 3,000 K
      • Emits longer-wavelength light
      • Appears red
properties of stars6
Properties of stars
  • Color and temperature
    • Between 5,000 and 6,000 K
      • Stars appear yellow
      • e.g., Sun
  • Binary stars and stellar mass
    • Binary stars
      • Two stars orbiting one another
        • Stars are held together by mutual gravitation
        • Both orbit around a common center of mass
properties of stars7
Properties of stars
  • Binary stars and stellar mass
    • Binary stars
      • Visual binaries are resolved telescopically
      • More than 50% of the stars in the universe are binary stars
      • Used to determine stellar mass
    • Stellar mass
      • Determined using binary stars – the center of mass is closest to the most massive star
properties of stars8
Properties of stars
  • Binary stars and stellar mass
    • Stellar mass
      • Mass of most stars is between 1/10 and 50 times the mass of the Sun
hertzsprung russell diagram
Hertzsprung-Russell diagram
  • Shows the relation between stellar
    • Brightness (absolute magnitude) and
    • Temperature
  • Diagram is made by plotting (graphing) each star’s
    • Luminosity (brightness) and
    • Temperature
hertzsprung russell diagram1
Hertzsprung-Russell diagram
  • 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)
      • Very luminous
      • Large
      • Upper-right on the H-R diagram
hertzsprung russell diagram2
Hertzsprung-Russell diagram
  • Parts of an H-R diagram
    • Giants (or red giants)
      • Very large giants are called supergiants
      • Only a few percent of all stars
    • White dwarfs
      • Fainter than main-sequence stars
      • Small (approximately the size of Earth)
      • Lower-central area on the H-R diagram
      • Not all are white in color
      • Perhaps 10% of all stars
variable stars
Variable stars
  • Stars that fluctuate in brightness
  • Types of variable stars
    • Pulsating variables
      • Fluctuate regularly in brightness
      • Expand and contract in size
    • Eruptive variables
      • Explosive event
      • Sudden brightening
      • Called a nova
interstellar matter
Interstellar matter
  • Between the stars is “the vacuum of space”
  • Nebula
    • Cloud of dust and gases
    • Two major types of nebulae
      • Bright nebula
        • Glows if it is close to a very hot star
        • Two types of bright nebulae
          • Emission nebula
          • Reflection nebula
interstellar matter1
Interstellar matter
  • Nebula
    • Two major types of nebulae
      • Dark nebula
        • Not close to any bright star
        • Appear dark
        • Contains the material that forms stars and planets
stellar evolution
Stellar evolution
  • 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
      • Gravity contracts cloud and temperature rises
      • Radiates long-wavelength (red) light
      • Becomes a protostar
stellar evolution1
Stellar evolution
  • Stages
    • Protostar
      • Gravitational contraction of gaseous cloud continues
      • Core reaches 10 million K
      • Hydrogen nuclei fuse
        • Become helium nuclei
        • Process is called hydrogen burning
      • Energy is released
      • Outward pressure increases
      • Outward pressure balanced by gravity pulling in
      • Star becomes a stable main-sequence star
stellar evolution2
Stellar evolution
  • Stages
    • Main-sequence stage
      • Stars age at different rates
        • Massive stars use fuel faster and exist for only a few million years
        • Small stars use fuel slowly and exist for perhaps hundreds of billions of years
      • 90% of a star’s life is in the main sequence
stellar evolution3
Stellar evolution
  • Stages
    • Red giant stage
      • Hydrogen burning migrates outward
      • Star’s outer envelope expands
        • Surface cools
        • Surface becomes red
      • Core is collapsing as helium is converted to carbon
      • Eventually all nuclear fuel is used
      • Gravity squeezes the star
stellar evolution4
Stellar evolution
  • Stages
    • Burnout and death
      • Final stage depends on mass
      • Possibilities
        • Low-mass star
          • 0.5 solar mass
          • Red giant collapses
          • Becomes a white dwarf
stellar evolution5
Stellar evolution
  • Stages
    • Burnout and death
      • Final stage depends on mass
      • Possibilities
        • Medium-mass star
          • Between 0.5 and 3 solar masses
          • Red giant collapses
          • Planetary nebula forms
          • Becomes a white dwarf
stellar evolution6
Stellar evolution
  • Stages
    • Burnout and death
      • Final stage depends on mass
      • Possibilities
        • Massive star
          • Over 3 solar masses
          • Short life span
          • Terminates in a brilliant explosion called a supernova
          • Interior condenses
          • May produce a hot, dense object that is either a neutron star or a black hole
stellar remnants
Stellar remnants
  • White dwarf
    • 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 remnants1
Stellar remnants
  • Neutron star
    • 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 remnants2
Stellar remnants
  • Neutron star
    • 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 remnants3
Stellar remnants
  • Black hole
    • More dense than a neutron star
    • Intense surface gravity lets no light escape
    • As matter is pulled into it
      • Becomes very hot
      • Emits X-rays
    • Likely candidate is Cygnus X-1, a strong X-ray source
  • Milky Way Galaxy
    • Structure
      • Determined by using radio telescopes
      • Large spiral galaxy
        • About 100,000 light-years wide
        • Thickness at the galactic nucleus is about 10,000 light-years
      • Three spiral arms of stars
      • Sun is 30,000 light-years from the center
  • Milky Way Galaxy
    • Rotation
      • Around the galactic nucleus
      • Outermost stars move the slowest
      • Sun rotates around the galactic nucleus once about every 200 million years
    • Halo surrounds the galactic disk
      • Spherical
      • Very tenuous gas
      • Numerous globular clusters
  • Other galaxies
    • Existence was first proposed in mid-1700s by Immanuel Kant
    • Four basic types of galaxies
      • Spiral galaxy
        • Arms extending from nucleus
        • About 30% of all galaxies
        • Large diameter up to 125,000 light-years
        • Contains both young and old stars
        • e.g., Milky Way
  • Other galaxies
    • Four basic types of galaxies
      • Barred spiral galaxy
        • Stars arranged in the shape of a bar
        • Generally quite large
        • About 10% of all galaxies
      • Elliptical galaxy
        • Ellipsoidal shape
        • About 60% of all galaxies
        • Most are smaller than spiral galaxies; however, they are also the largest known galaxies
  • Other galaxies
    • Four basic types of galaxies
      • Irregular galaxy
        • Lacks symmetry
        • About 10% of all galaxies
        • Contains mostly young stars
        • e.g., Magellanic Clouds
  • Galactic cluster
    • Group of galaxies
    • Some contain thousands of galaxies
    • Local Group
      • Our own group of galaxies
      • Contains at least 28 galaxies
    • Supercluster
      • Huge swarm of galaxies
      • May be the largest entity in the universe
red shifts
Red shifts
  • Doppler effect
    • Change in the wavelength of light emitted by an object due to its motion
      • Movement away stretches the wavelength
        • Longer wavelength
        • Light appears redder
      • Movement toward “squeezes” the wavelength
        • Shorter wavelength
        • Light shifted toward the blue
red shifts1
Red shifts
  • Doppler effect
    • Amount of the Doppler shift indicates the rate of movement
      • Large Doppler shift indicates a high velocity
      • Small Doppler shift indicates a lower velocity
  • Expanding universe
    • Most galaxies exhibit a red Doppler shift
      • Moving away
red shifts2
Red shifts
  • Expanding universe
    • Most galaxies exhibit a red Doppler shift
      • Far galaxies
        • Exhibit the greatest shift
        • Greater velocity
      • Discovered in 1929 by Edwin Hubble
      • Hubble’s Law – the recessional speed of galaxies is proportional to their distance
      • Accounts for red shifts
big bang theory
Big Bang theory
  • Accounts for galaxies moving away from us
  • Universe was once confined to a “ball” that was
    • Supermassive
    • Dense
    • Hot
big bang theory1
Big Bang theory
  • Big Bang marks the inception of the universe
    • Occurred about 15 billion years ago
    • All matter and space was created
  • Matter is moving outward
  • Fate of the universe
    • Two possibilities
      • Universe will last forever
      • Outward expansion will stop and gravitational contraction will follow
big bang theory2
Big Bang theory
  • Fate of the universe
    • Final fate depends on the average density of the universe
      • If the density is more than the critical density, then the universe would contract
      • Current estimates point to less than the critical density and predict an ever-expanding, or open, universe