stars a self-luminous celestial body consisting of a mass of gas held together by its own gravity in...
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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
Massive luminous balls of plasma
held together by gravity
Stars
Characteristics of Stars
a. Colorb. Temperaturec. Mass
We use these characteristics to understand and examine stars
a. Color
• Color is a clue to a star’s temperature.
• Blue stars are hotter/ newer/closer
• Red stars are cooler/older/more distant
b. Temperature• Very hot stars emit short-
wavelength lightBLUE
• Cooler stars emit long-wavelength light
RED
c. Mass - A unified body of matter with no specific shape
• Mass is how much “stuff” is squeezed into a space
Japan subway car without much “stuff” inside =Less Mass
Crowded Japan subway car with lots of “stuff” =
More mass
Lots of “stuff” squeezed into a space, place or thing
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 – It’s mass
If the sizes of the orbits are known
Then the stars mass can be determined
Hertzsprung-Russell Diagram
• Shows the relationship between the absolute magnitude and the temperature of stars
• 90 % main-sequence stars
• Giants• Supergiants• White dwarfs
Light Year – the distance light travels in 1 year
• 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
9.5 x 10 to the 12th powerOr
9.5 trillion kilometersOr
186000 miles per second
Measuring distance to stars – it’s difficultThe most basic way to measure distance to stars is parallax.
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
Apparent Magnitude - a stars brightness as it appears from Earth
3 factors control the brightness from Earth
1. How big2. How hot3. How far away
Absolute Magnitude – how bright a star actually is
Variable Stars – some stars fluctuate in brightness
1. Cepheid – gets brighter in a variable pattern
2. Nova – sudden brightening of a star due to a flare up
Interstellar Matter - between existing stars is “the vacuum of space”
Except for Nebulae…
Nebulae – clouds of dust, gas, and thinly scattered matter
• Stars and planets form from this interstellar matter
1.Nebulae begin to contract– Gravity squeezes
particles in the nebula towards the center
– Nebula shrinks – Gravitational energy is
converted into heat energy
Protostar Stage – a developing star not hot enough to begin nuclear fusion
1. Contraction lasting 1 million years
2. Collapse causes the core to heat more than the outer layer– Causes gas to increase
it’s motion3. When the core reaches
10 million K, nuclear fusion of hydrogen begins
4. A star is born
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 star’s hydrogen fuel in
the core is depleted, it evolved rapidly and dies.
– Some stars delay death by burning heavier elements and become giants
Gravity (external force)Gas (internal force)
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 it’s original main-sequence size
Death and Burnout of Stars• All stars run out of fuel and collapse because of
gravity
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
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
Death of Massive Stars• Massive stars have short
lives• End star life in brilliant
explosions called supernova
• Rare1. Death is triggered when
nuclear fuel is consumed2. Star collapses 3. Implodes4. 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
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
Study of Light
Information about the universe is obtained from the study of the light emitted from stars and other bodies in space
Electromagnetic Radiation
1. Gamma Rays2. X-Rays3. Ultraviolet Rays4. Visible Light5. Infrared Radiation6. Microwaves7. Radio waves
All energy travels through the vacuum of space at the speed of light
Electromagnetic Spectrum – arrangement of waves according to their wavelengths and frequencies
1. Wavelengths 2. Photons – a
stream of particles
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
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