Download Volcanoes and Igneous Activity Earth

Beyond the Solar System
Chapters 23 and 24
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Stellar parallax
© 2011 Pearson Education, Inc.
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 kilometers (5.8
trillion miles)
© 2011 Pearson Education, Inc.
Properties of stars
• Stellar brightness
• Controlled by three factors
• Size
• Temperature
• Distance
• Magnitude
• Measure of a star’s brightness
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Properties of stars
• Color and temperature
• Hot star
• Temperature above 30,000 K
• Emits short-wavelength light
• Appears blue
• Cool star
• Temperature less than 3000 K
• Emits longer-wavelength light
• Appears red
© 2011 Pearson Education, Inc.
Properties of stars
• Color and temperature
• Between 5000 and 6000 K
• Stars appear yellow
• 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
© 2011 Pearson Education, Inc.
Properties of stars
• Binary stars and stellar mass
• Binary stars
• Visual binaries are resolved telescopically
• More than 50 percent 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
© 2011 Pearson Education, Inc.
Binary stars orbit
each other
around their
common center
of mass
© 2011 Pearson Education, Inc.
Properties of stars
• Binary stars and stellar mass
• Stellar mass
• Mass of most stars is between one-tenth and fifty
times the mass of the Sun
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Idealized HertzsprungRussell diagram
© 2011 Pearson Education, Inc.
Hertzsprung-Russell diagram
• Parts of an
Hertzsprung-Russell (H-R) diagram
• Main-sequence stars
• 90 percent 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
© 2011 Pearson Education, Inc.
Hertzsprung-Russell diagram
• Parts of an
Hertzsprung-Russell (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 (approximate the size of Earth)
Lower-central area on the H-R diagram
Not all are white in color
Perhaps 10% of all stars
© 2011 Pearson Education, Inc.
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 close to a very hot star
• Two types of bright nebulae
• Emission nebula
• Reflection nebula
© 2011 Pearson Education, Inc.
The Trifid Nebula, in the
constellation Sagittarius
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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 the cloud
Temperature rises
Becomes a protostar
© 2011 Pearson Education, Inc.
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 balanced by gravity pulling in
– Star becomes a stable main-sequence star
© 2011 Pearson Education, Inc.
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 percent of a star’s life is in the main-sequence
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Evolutionary stages of
low-mass stars
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Evolutionary stages of
medium-mass stars
© 2011 Pearson Education, Inc.
H-R diagram showing
stellar evolution
© 2011 Pearson Education, Inc.
Stellar evolution
• Stages
• Burnout and death
• Final stage depends on mass
• Possibilities
• Massive star
• Over 3 solar masses
• 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
© 2011 Pearson Education, Inc.
Evolutionary stages of
massive stars
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Galaxies
• 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
© 2011 Pearson Education, Inc.
Face-on view of the
Milky Way galaxy
© 2011 Pearson Education, Inc.
Edge-on view of the
Milky Way galaxy
© 2011 Pearson Education, Inc.
Galaxies
 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
© 2011 Pearson Education, Inc.
Galaxies
• Three basic types of galaxies
• Spiral galaxy
•
•
•
•
•
Arms extending from nucleus
About 30 percent of all galaxies
Large diameter of 20,000 to 125,000 light years
Contains both young and old stars
e.g., Milky Way
© 2011 Pearson Education, Inc.
Andromeda Galaxy, a large spiral galaxy
© 2011 Pearson Education, Inc.
A barred spiral galaxy
© 2011 Pearson Education, Inc.
Galaxies
• Three basic types of galaxies
• Elliptical galaxy
• Ellipsoidal shape
• About 60 percent of all galaxies
• Most are smaller than spiral galaxies; however,
they are also the largest known galaxies
© 2011 Pearson Education, Inc.
Galaxies
• Three basic types of galaxies
• Irregular galaxy
•
•
•
•
Lacks symmetry
About 10 percent of all galaxies
Contains mostly young stars
e.g., Magellanic Clouds
© 2011 Pearson Education, Inc.
Galaxies
• 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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Big Bang theory
• Accounts for galaxies moving away from us
• Universe was once confined to a “ball”
that was
• Supermassive
• Dense
• Hot
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.