Download Exploring The Universe

Exploring The Universe
Student Guided Notes
Ch. 20 Sec.1
STARS
• Objectives:
– Classify stars according to chemical and
physical properties
– Interpret an H-R diagram.
What are STARS?
• Star
– a large celestial body that is composed of gas and
that emits light; the sun is a typical star
• Light-year
– the distance that light travels in one year; about 9.5
trillion kilometers
• Stars are huge spheres of hot gas.
• The nearest star to the Earth is the sun.
• We use the unit light-year to describe a star’s
distance from Earth.
How do we classify STARS?
• Scientists classify stars according to their:
– Color
– Size
– Brightness
How do we classify STARS?
• Scientists classify stars according to their:
– Color
– Size
– Brightness
Copy this
table
down!!!
Above 30,000o
Celsius
5000o-6000o
Celsius
3000o C
BLUE
Yellow
RED
How do we classify STARS?
• Scientists classify stars according to their:
– Color
– Size
– Brightness
• Apparent Brightness:
– Decreases as its distance from you increases
• The brightness of a star as it appear from
Earth
Apparent Brightness:
Absolute Brightness:
• How bright a star REALLY is regardless of
its distance from Earth.
• Absolute brightness is a characteristic of a
star
Apparent
Brightness
Absolute
Brightness
How do we classify STARS?
• Scientists classify stars according to their:
– Color
– Size
– Brightness
• Temperature & Absolute Brightness help us
figure out a star’s VOLUME
• Gravitational attraction of stars that appear in
pairs helps us figure out its MASS
• There is a relationship between mass &
absolute brightness
How do we know what elements
are in STARS?
• Spectrograph:
– An instrument that spreads light from a hot glowing
object into a band of colors called a spectrum.
• Spectral lines reveal the composition of stars.
• The spectra of most stars have dark lines caused by
gases in the outer layers that absorb light at that
wavelength.
• Each element produces a unique pattern of spectral
lines.
How do we know what elements
are in a STAR?
• Astronomers can match the dark lines in
starlight to the known lines of elements found
on Earth.
Absorption
Lines
H-R Diagrams
Early 1900’s:
• Ejnar Hertzprung & Henry Norris Russell
(working independently) Noticed:
• Stars can be classified by graphing them
according to their
surface temperature (color) and absolute
brightness.
H-R Diagram
H-R Diagram
• Two factors
determine a star’s
absolute brightness:
– Size
– Surface temperature
• The H-R diagram
shows temperature
& absolute
brightness
– We can use it to infer
a star’s size.
Types of Stars:
• Main Sequence Stars
• Supergiants
• Giants
• White Dwarfs
Main Sequence Stars
• Range from bright & hot to dim & cool
• Over 90% of stars are classified this way
• Over 90% of a star’s lifetime is spent in this
stage.
Diagonal band in the
middle of the H-R Diagram
•The Sun lies near the
middle of this band
Super Giants
• Very Bright
• Much Brighter than main sequence stars of
the same temp.
• Very Large
Red Giants
• Large & Bright
• Fainter than Supergiants.
White Dwarfs
• Small, dense remains of low to
medium mass stars
• Hot, but dimmer
than main
sequence stars of
the same temp.
Exploring the Universe
Part II
Life Cycle of Stars
Life Cycles of Stars
• Objectives:
– Describe how stars form.
– Estimate how long a star remains in the main
sequence stage.
– Predict what happens to a star when it runs
out of fuel.
Birth of a Star
1. A star begins as a cloud
of dust & hydrogen gas.
•
Cloud of
Hydrogen gas
NEBULA
2. As gravity pulls the
clouds together, a
dense, hot core is
formed
3. Temps increase in core.
Hydrogen atoms smash
into each other
Cloud pulls
Together &
Forms a
Dense, hot core
Birth of a Star
4. When temp is hot
enough, hydrogen begin
FUSING to form helium.
5. Nuclear Fusion
generates huge
amounts of energy.
6. Leftover dust & gas
dissipates, leaving the
star behind.
Nuclear….
Fusion begins
& the core…
Becomes a
Star…..
Cloud…..
Dissipates,
Leaving star
Behind...
Life Cycle of a Star
• Lifetime depends on size of star.
– Large, heavy stars burn up their hydrogen
(fuel) faster than smaller stars do.
– Therefore, large (massive) stars burn out
faster than small stars.
Life Cycle of an Average Star
• Death
– When Hydrogen is used up, the core
collapses on itself causing temp to rise.
– Heat from core makes outer layers expand
– Any remaining hydrogen is burned up.
Life Cycle of an Average Star
• Collapse
– When all Hydrogen is used up, the star
collapses on itself.
– Resulting in a WHITE DWARF.
Life Cycle of a Massive Star
• Death
– When Hydrogen is used up, the core
collapses on itself causing temp to rise.
– Heat from core makes outer layers expand
– Any remaining hydrogen is burned up.
Life Cycle of a Massive Star
• Supernova
– When the supergiant starts to collapse, there
is a huge & sudden explosion.
– Everything except the core is blown outward
into space.
• This exploded material is used to start new stars &
solar systems.
Life Cycle of a Massive Star
• Collapse
– Remaining star’s core becomes a dense,
invisible pulsar sending out pulsing radio waves.
– When pulsar stops pulsing, it becomes a neutron
star.
– Neutron star eventually collapses further,
becoming a black hole.
Exploring the Universe
Part III
Galaxies
The Milky Way and Other Galaxies
Galaxies
• Galaxies contain millions or billions of
stars.
• Galaxy a collection of stars, dust, and gas
bound together by gravity
• Because stars age at different rates, a
galaxy may contain many types of stars.
The Milky Way and Other Galaxies
Galaxies, continued
• Gravity holds galaxies together in clusters.
• Galaxies are not spread evenly throughout
space.
The Milky Way and Other Galaxies
Galaxies, continued
• Cluster a group of stars or galaxies bound
by gravity
• The Milky Way galaxy and the Andromeda
galaxy are two of the largest members of the
Local Group, a cluster of more than 30
galaxies.
• Clusters of galaxies can form even larger
groups, called superclusters.
The Milky Way and Other Galaxies
Types of Galaxies
• We live in the Milky Way galaxy.
• Edwin Hubble divided all galaxies into three
major types: spiral, elliptical, and irregular.
• Most of the objects visible in the night sky are
part of the Milky Way galaxy.
• Scientists use astronomical data to piece
together a picture of the Milky Way galaxy.
The Milky Way and Other Galaxies
Galaxies,
• Types
The MilkyofWay
is a spiral continued
galaxy.
• Our galaxy is a huge spiraling disk of stars, gas,
and dust.
• Our solar system is located within a spiral arm.
• The nucleus of the galaxy is dense and has many
old stars, while the arms have younger stars.
• Interstellar matter the gas and dust
located between the stars in a galaxy.
Spiral Galaxies
The Milky Way and Other Galaxies
Types of Galaxies, continued
• Eliptical galaxies have no spiral arms.
• Elliptical galaxies are spherical or egg
shaped.
• They contain mostly older stars and have
little interstellar matter.
• Because older stars are red, elliptical galaxies
often have a reddish color.
Elliptical Galaxy
The Milky Way and Other Galaxies
Types of Galaxies, continued
• All other galaxies are irregular galaxies.
• Irregular galaxies lack regular shapes and do
not have a well-defined structure.
• Some irregular galaxies may be oddly shaped
because the gravitational pull of nearby
galaxies distorts their spiral arms.
• Contain mostly YOUNG STARS
Irregular Galaxy
How do Galaxies FORM?
• Quasars may be infant galaxies.
• In 1960, a faint object was matched with a
strong radio signal. This object was called a
quasar.
• quasar quasi-stellar radio sources; very
luminous objects that produce energy at a high
rate and that are thought to be the most distant
objects in the universe
• Each quasar has a huge central black hole and
a large disk of gas and dust around it.
How do Galaxies FORM?
• Galaxies change over time.
• Galaxies change as they use up their stores
of gas and dust
• Galaxies also change as a result of
collisions.
• As galaxies approach each other, mutual
gravitational attraction changes their shape.
• Collisions of gas and dust may cause new
stars to begin forming.
Exploring the Universe
Part IV
Origins of the Universe
Origins of the Universe
• Universe the sum of all space, matter,
and energy that exist, that have existed in
the past, and that will exist in the future.
• You are part of the universe, as is Earth
and everything on it.
Origins of the Universe
• We see the universe now as it was in the
past.
• It takes time for light to travel in space.
• The farther away an object is, the older the
light that we receive from that object.
• Most of the universe is empty space
Origins of the Universe
• The universe is expanding.
• Observations of spectral lines from other
galaxies indicated that they were moving
away from us
Origins of the Universe
• Red shift a shift toward
the red end of the light
spectrum caused when
objects move away from
the observer
• Blue shift a shift toward
the blue end of the light
spectrum caused when
objects move toward the
observer
Birth of the Universe
• Expansion implies that the universe was
once smaller.
• All of the matter in the universe appears to
expand rapidly outward, like a gigantic
explosion
• Scientists call this hypothetical explosion the
big bang.
Birth of the Universe
• Cosmic background radiation supports
the big bang theory.
• Cosmic background radiation is a signal from
all over the sky in the form of microwave
radiation.
• Many scientists believe that the microwaves
are dim remains of the radiation produced
during the big bang.
Birth of the Universe
• Processes in stars
lead to bigger atoms.
• Once hydrogen
atoms formed, stars
and galaxies began to
form, too.
• All elements other
than hydrogen and
helium form in stars.
The FUTURE of the Universe
• The future of the universe is uncertain.
• The universe is expanding,
•
but the gravity of all the mass in the universe
is also pulling the universe inward.
• So what’s going to happen?
The FUTURE of the Universe
• The competition between these forces
leaves three possibilities:
•
The universe will keep expanding forever
•
The expansion of the universe will gradually slow
down, and the universe will stay the same size.
•
The universe will stop expanding and start to fall
back in on itself
The FUTURE of the Universe
• The fate of the universe depends on mass.
• If there is not enough mass, the gravitational
pull will be too small to stop the expansion.
• The right amount of mass, the expansion will
continually slow down, but will never stop
completely.
• Too much mass, gravity will eventually
overcome expansion and the universe will
contract.
The FUTURE of the Universe
• There is a debate
about dark matter.
• There is more matter
in the universe than
what is visible.
• Scientists call this
dark matter.
• Dark matter may be:
• Planets
• black holes
• brown dwarfs
(starlike objects that lack
enough mass to begin
fusion.)