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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


Earth science 12e

  • 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 mass

  • 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 mass-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 mass-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 mass-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


Idealized hertzsprung russell diagram
Idealized massHertzsprung-Russell diagram

Figure 24.7


Variable stars
Variable stars mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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


H r diagram showing stellar evolution
H-R diagram showing massstellar evolution

Figure 24.11


Stellar evolution6
Stellar evolution mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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)


Crab nebula in the constellation taurus
Crab Nebula in the massconstellation Taurus

Figure 24.14


Stellar remnants3
Stellar remnants mass

  • 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


Galaxies
Galaxies mass

  • 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


Face on view of the milky way galaxy
Face-on view of the massMilky Way Galaxy

Figure 24.18 A


Edge on view of the milky way galaxy
Edge-on view of the massMilky Way Galaxy

Figure 24.18 B


Galaxies1
Galaxies mass

  • 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


Galaxies2
Galaxies mass

  • 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



Galaxies3
Galaxies mass

  • 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


A barred spiral galaxy
A barred spiral galaxy mass

Figure 24.22


Galaxies4
Galaxies mass

  • Other galaxies

    • Four basic types of galaxies

      • Irregular galaxy

        • Lacks symmetry

        • About 10% of all galaxies

        • Contains mostly young stars

        • e.g., Magellanic Clouds


Galaxies5
Galaxies mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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 mass

  • 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