Star Properties

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Star Properties
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Star Distances

• Units of Distance for Space
• Astronomical Units (AU) The distance from the
  earth to the sun (150,000,000 km)
• Light Years Distance light travels in a year.
• 9.4 trilliion km

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Physical Properties of Stars Size and Density

• Color , temperature, size and density vary
  greatly between stars.
• Some are smaller than earth, others are 2000
  times wider than the sun

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Elements in Stars

• Stars are mainly 99 Hydrogen (H) and Helium (He)
• 1-2 may be heavier elements like Oxygen, Carbon,
  Nitrogen, Calcium
• Sun is 70 Hydrogen and 28 Helium
• Stars produce energy (heat and light) by fusing
  hydrogen atoms to make helium

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Star Color

• The color of the star is dependant on its surface
  temperature.
• Hot stars Blue or White, 30,000 K
• Cool stars Red or Orange, 3,000 K
• The Sun Orange or Yellow, 5,500 K

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Star Brightness

• Luminosity
• How bright a star actually is.
• Dependant on the size and temperature of the
  star.
• Hotter Brighter
• Bigger Brighter

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Star Brightness

• Apparent Magnitude How bright the star appears
  to be to an observer on Earth.
• Ranking 1st to 6th, 1st being brightest
• A 1st is 100x brighter than a 6th magnitude
• Absolute Magnitude The luminosity of stars if
  they were all seen from the same distance (32.6
  light years from the sun)

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Star Types

• Nebula a cloud of dust and gas that stars are
  born out of most are invisible

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2 Visible types of Nebulas

• Diffuse Nebula visible due to the light provided
  by close stars
• Dark Nebula A nebula that you can see blocking
  other stars

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Star Types

• Protostars baby stars that appear as a nebula
  contracts and heats up.
• Main Sequence/Stable State Young stars that are
  still mostly hydrogen that is fusing into helium
• Stars in The prime of their life
• The more mass, the hotter

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Star Types

• Giants Highly luminous due to their overwhelming
  size
• Supergiant Largest and brightest of all stars
• Dwarfs Small, less luminous stars
• Can still be very hot, but dim because they are
  so small

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• Test ? Tomorrow (Tuesday 10/19)
• Stars, Galaxies, Universe
• Review Sheet Due Tomorrow
• Constellations Presentations Start Wednesday
• (Laranda_at_cps.edu)

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Star Life Cycle Activity

• Diagram and describe YOUNGEST to OLDEST in
  order.
• Nebula,
• Protostar
• Main Sequence
• Giant/Supergiant
• Dwarf
• Supernova
• Neutron
• Black Hole

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Determine Star Color Type.
D
C
B
A
Low Temp
High Temp
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Origin of Stars

• Start as huge clouds of gas and dust (nebulae)
• Gas clouds originated from supernovas

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Formation of Protostars

• Something outside the nebula triggers the gravity
  between the gasses and dust
• As the nebula contracts, spots begin to glow with
  heat, forming protostars.

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Formation of Main Sequence Stars

• As protostars continue to contract, they get
  hotter and brighter until fusion begins.
• IMPORTANT STARS ARE ALWAYS TRYING TO COLLAPSE
  DUE TO THEIR OWN GRAVITY
• Stars release energy equal to the force of
  gravity, which stops the contracting
• It is now a Main Sequence Star

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Formation of Giants/Supergiants

• When hydrogen is almost depleted, the energy of
  fusion no longer balances the force of gravity.
• Core of the star contracts and increases in heat.
  
• Increased energy causes the outer layers to
  expand creating a Giant/Supergiant

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Formation of Dwarfs

• With no fuel, no energy is released to support
  the outer layers of the star
• THE STAR COLLAPSES ON ITSELF DUE TO GRAVITY
• This squeezes the nuclei together very tightly
  and it becomes a dwarf
• Causing the star to glow for billions of years as
  they cool

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Massive Star Life Cycle Supernova

• When fusion stops in very MASSIVE STARS, a super
  dense central iron core is left.
• The cores gravity is so strong that it collapses
  further, increasing pressure.
• All the pressure on the core makes the star
  explode violently and half its mass is blown away
  in a great cloud called a supernova

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Supernova Before and After
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Neutron stars

• The leftover half of supernova.
• Its gravity is so strong that all of the atoms
  particles are crushed together, leaving only
  neutrons.
• Neutron stars may be 10km wide but are a
  trillions times as dense as the sun.

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Black Holes

• If the neutron star is massive enough, its
  gravity causes it to collapse, creating Black
  Holes.
• Gravity is so great that not even light can
  escape
• Gathering evidence supports the theory that the
  central core of the galaxy is a black hole

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If we cant see them, how do we know that they
are there?

• Strong X-Ray emissions from the Cygnus
  constellation were detected.
• Upon observation, we saw a star orbiting around
  an empty spot in space
• When something gets sucked into a black hole, its
  atoms get ripped apart and it emits x-rays
• This was what was happening to the stars matter
• It is believed that the center of our galaxy and
  many others are massive black holes

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Galaxies and Universe
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Starting small

• Solar system the sun and its orbiting planets,
  asteroids, meteors, and comets.
• Galaxy groups of millions or billions of stars
  held together by gravity.
• Universe contains all the planets, stars, solar
  systems, and galaxies.

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The Milky Way

• Sun is 1 of 100 billion stars in the Milky Way
  galaxy
• It is 1 of 17 nearby galaxies that make up the
  Local Group

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Milky Way Facts

• Diameter 140,000 light years
• 1 light year 9,460,730,472,580.8 km
• Width 20,000 light years
• Sun is 23,000 light years from the center

Thats Us!
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Galaxy Types Spiral Galaxies

• Spiral Galaxies have a central nucleus made of
  millions of stars
• Have arms extending from the nucleus, (made of
  clouds of dust gas)
• 75 of known galaxies are spiral.

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Barred Spiral Galaxies

• Same as spiral galaxies, except they have a bar
  that goes through the middle.

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Which is Which?
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Elliptical Galaxies

• Elliptical Galaxies range from spherical to lens
  shaped
• Contain no gas and dust clouds

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Irregular Galaxies

• Irregular Galaxies are smaller, fainter, and less
  common Stars have no pattern

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The Origin of the Universe

• Big-Bang Theory
• Universe started as 1 dense sphere of hydrogen
• 13.7 bya it exploded, forming an expanding cloud
  of gas dust
• Cloud parts condensed into stars. Stars joined
  with other stars to become galaxies

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Evidence for the Big Bang

• 1. Edwin Hubble discovered that the light of
  distant stars is constantly becoming more red.
• Red Shift ? the object producing the light is
  moving away from us
• 2. Microwaves coming from all directions in the
  universe
• Echoes of the original explosion

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What is Dark Matter?