The Life Cycle of Stars: Chapter 8, Section 2

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The Life Cycle of Stars Chapter 8, Section 2
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What we are going to learn today about the life
cycle of Stars

• The different types of stars
• How to read an H-R diagram
• How stars appear at different stages in their
  life cycle on the H-R diagram.

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The Beginning and End of Stars

• The Beginning A star enters the first stage of
  its life cycle as a ball of gas and dust. Gravity
  pulls the gas and dust together, and hydrogen
  changes to helium in a processes called nuclear
  fusion.
• The End Stars usually lose material slowly, but
  sometimes they can lose material in a big
  explosion. Much of a stars material returns to
  space, where it sometimes forms new stars..
• How many stars are estimated to
• be in our Milky Way Galaxy?
• 200,000,000,000

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Different Types of Stars

• Stars can be classified by their size, mass,
  brightness, color, temperature, spectrum, and
  age. A stars classification can change as it
  ages.
• Main-Sequence Stars After a star forms, it
  enters the second and longest stage of its life
  cycle known as the main sequence. Energy is
  generated in the core as hydrogen atoms fuse into
  helium atoms.
• What kind of star is our sun??

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Main Sequence Star SystemAlpha Centauri, 25
trillion miles away
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Red Giants

• A red giant is a large, reddish (usually main
  sequence) star late in its life cycle, or third
  stage.
• As the center of the star shrinks, the
  atmosphere of the star grows very large and
  cools to form a red giant or a red supergiant.
• This is Betelgeuse, a red giant star
• in the Milky Way. Who has seen
• it through a telescope? In what
• Constellation is it located?

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Orion Constellation
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White Dwarf Stars

• In the final stage of its life cycle, a star that
  has the same mass as the sun (main sequence star)
  or smaller can be classified as a white dwarf.
• A white dwarf is a small, hot dim star that is
  the leftover center of an old star.
• It has no hydrogen left and cannot generate
  energy any more by nuclear fusion, but it can
  shine for billions of years before cooling
  completely.
• In what constellation is there
• a white dwarf in our galaxy?
• White Dwarf Stars

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White Dwarf SiriusBlue Supergiant Rigel
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H-R Diagram A graph for studying the stars

• The H-R Diagram (Hertzprung-Russell diagram) is a
  graph that shows the relationship between a
  stars surface temperature and its absolute
  magnitude.
• Reading the H-R Diagram The diagonal pattern on
  the H-R diagram where most stars lie, is called
  the main sequence.
• Where is our sun?
• The main sequence
• is the location on
• the diagram where
• most stars lie

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H-R Diagram

• How hot is the surface of the sun?
• 5,000 6,000 C or 10,000 F

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• According to the H-R diagram, what types of
  stars have very low temperatures and high
  absolute magnitudes?
• A blue stars
• B red giants
• C white dwarfs

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When stars get old

• When main sequence stars get old (such as our
  sun) they become red giants and then white dwarfs
  at the end of their life cycle.
• Massive stars, however, generate much more energy
  and also dont last as long.
• Massive stars may explode with such intensity
  that they may become supernovas, neutron stars,
  pulsars, or black holes.
• What will our sun probably become in its next
  stage?

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Supernovas

• A supernova is a gigantic explosion in which a
  massive star collapses and throws its outer
  layers into space.
• Supernova NGC 6826
• Its green gas is almost
• half of its mass.

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Neutron Star

• After the supernova explosion, the center of the
  collapsed star contracts to form a new star. It
  has been smashed together so forcefully that all
  of its particles have become neutrons.

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Pulsars

• When a neutron star is rapidly spinning, it is
  called PULSAR. It emits rapid pulses of radio
  waves and optical energy.
• This is Pulsar B1509. It is spinning so
  rapidly(7 rotations/sec), 12 miles wide, it
  creates a hand-shaped nebula

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Black Holes

• Sometimes the leftovers of a supernova are so
  massive that they collapse to form a black hole.
  A black hole is an object that is so massive
  that even light cannot escape its gravity.
• Black Holes are invisible their extreme gravity
  can cause light to stretch their spinning can
  drag the very fabric of space around with it

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Who took these pictures?

• These images were taken from the ALMA telescope,
  CHANDRA satellite and the Hubble Space
  telescope.
• ALMA is a radio telescope in Chile
• CHANDRA is a satellite launched by NASA in 1999
• The Hubble is an orbiting observatory that was
  launched by the Space Shuttle Discovery in 1990

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Lets see how much you know about Stars now!

• What are some different types of stars?
• What does an H-R diagram tell us?
• What can main sequence stars (like our sun) turn
  into as they get old?
• What are some things massive stars become?