Stars

1
Stars

• A self-luminous celestial body consisting of a
  mass of gas held together by its own gravity in
  which the energy generated by nuclear reactions
  in the interior is balanced by the outflow of
  energy to the surface, and the inward-directed
  gravitational forces are balanced by the
  outward-directed gas and radiation pressures

2
Massive luminous balls of plasma held together
by gravity
Stars
3
Characteristics of Stars

• Color
• Temperature
• Mass
• We use these characteristics to understand and
  examine stars

4
Color

• Color is a clue to a stars temperature.
• Blue stars are hotter/ newer/closer
• Red stars are cooler/older/more distant

5
b. Temperature

• Very hot stars emit short-wavelength light
• BLUE
• Cooler stars emit long-wavelength light
• RED

6
c. Mass - A unified body of matter with no
specific shape

• Mass is how much stuff is squeezed into a space

7
Japan subway car without much stuff inside
Less Mass
8
Crowded Japan subway car with lots of stuff
More mass
Lots of stuff squeezed into a space, place or
thing
9
Binary Stars pairs of stars pulled toward each
other by gravity

• Many stars orbit each other
• More than 50 of stars occur in pairs or
  multiples.
• Binary stars are used to determine the star
  property most difficult to calculate Its mass

10
If the sizes of the orbits are known
Then the stars mass can be determined
11
Hertzsprung-Russell Diagram

• Shows the relationship between the absolute
  magnitude and the temperature of stars
• 90 main-sequence stars
• Giants
• Supergiants
• White dwarfs

12
Light Year the distance light travels in 1 year
9.5 x 10 to the 12th power Or 9.5 trillion
kilometers Or 186000 miles per second

• Distances to stars are so large that units like
  miles or kilometers are too hard to use
• The numbers get really, really confusing and big

13
Measuring distance to stars its difficult

• The most basic way to measure distance to stars
  is parallax.

14
Parallax the slight shifting of a nearby star
due to the orbital motion of Earth
uses photographs of stars to compare to distant
stars in the backgroundshifting angles are
comparedthe angles compared are very small
Close stars large parallax angles Distant
stars smaller parallax angles
15

• Apparent Magnitude - a stars brightness as it
  appears from Earth

• 3 factors control the brightness from Earth
• How big
• How hot
• How far away

16
Absolute Magnitude how bright a star actually is
17
Variable Stars some stars fluctuate in
brightness

• Cepheid gets brighter in a variable pattern
• Nova sudden brightening of a star due to a
  flare up

18
Interstellar Matter - between existing stars is
the vacuum of space
Except for Nebulae
19
Nebulae clouds of dust, gas, and thinly
scattered matter

• Stars and planets form from this interstellar
  matter
• Nebulae begin to contract
• Gravity squeezes particles in the nebula towards
  the center
• Nebula shrinks
• Gravitational energy is converted into heat
  energy

20
Protostar Stage a developing star not hot
enough to begin nuclear fusion

• Contraction lasting 1 million years
• Collapse causes the core to heat more than the
  outer layer
• Causes gas to increase its motion
• When the core reaches 10 million K, nuclear
  fusion of hydrogen begins
• A star is born

21
Main-Sequence Star a star balanced between 2
forces, gravity and gas pressure

• Gravity(external force)
• Gas (internal force)
• Hydrogen fusion lasts a few billion years
• 90 of an average stars life is in this hydrogen
  burning stage
• When a stars hydrogen fuel in the core is
  depleted, it evolved rapidly and dies.
• Some stars delay death by burning heavier
  elements and become giants

22
Gravity (external force) Gas (internal force)
23
Red Giant Stage

• Inner Core consumes all hydrogen fuel energy and
  begins to contract
• Helium core is left behind
• Core contracts and heat is radiated outward.
• This energy heats the outer layer and causes
  expansion
• Results in giant body size of star 100 to 1000 X
  size of its original main-sequence size

24
Death and Burnout of Stars

• All stars run out of fuel and collapse because of
  gravity

25
Death of Low Mass Stars

• Small
• Cool
• Red
• Consume hydrogen fuel slowly
• Not hot enough to fuse helium
• Remain on the main sequence for up to 100 billion
  years
• Collapse into White Dwarfs

26
Death of Medium Mass Stars

• Masses similar to our Sun
• Evolve into Giants
• consume hydrogen and helium at fast rate
• Collapse into White Dwarfs
• During collapse from Red Giant into White Dwarf
  they cast off their outer shell and leave a cloud
  of gas called planetary nebulae

27
Death of Massive Stars

• Massive stars have short lives
• End star life in brilliant explosions called
  supernova
• Rare
• Death is triggered when nuclear fuel is consumed
• Star collapses
• Implodes
• Sends shock wave out from the stars interior,
  this destroys the star blasting the shell into
  space
• None have been observed since the invention of
  the telescope

28
Nucleosynthesis the process that produces
chemical elements inside stars

• Occurs in dying stars
• Stars produce all naturally occurring elements
  beyond helium in the periodic table
• Mass of the star determines the highest atomic
  number of the elements it can produce
• More massive stars produce heavier elements

29
Study of Light
Information about the universe is obtained from
the study of the light emitted from stars and
other bodies in space
30
Electromagnetic Radiation

1. Gamma Rays
2. X-Rays
3. Ultraviolet Rays
4. Visible Light
5. Infrared Radiation
6. Microwaves
7. Radio waves

All energy travels through the vacuum of space at
the speed of light
31
Electromagnetic Spectrum arrangement of waves
according to their wavelengths and frequencies

1. Wavelengths
2. Photons a stream of particles

32
When the spectrum of a star is studied, the
spectral lines act as fingerprints. Spectral
lines identify the elements present in a star and
tell of the stars chemical composition