Basic Properties of Stars :Stellar Lives.

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• Basic Properties of Stars Stellar Lives.

• Stellar Temperatures
• The Hertzsprung-Russell Diagram
• Groups of Stars and Their Lives

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Terms

• Kelvin Scale
• Absolute zero is 0K
• To convert from Farenheit
• F 459.67 /1.8

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Kelvin Scale examples

• Absolute zero- 0K
• Freezing point of water- 273.16K
• Surface of Earth- 288K
• Boiling Point of water- 373.16K
• Surface of Mercury 445K
• Surface of M star 3,500K
• Surface of Sun 5, 700K

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Luminosity

• The Luminosity of a star depends on BOTH its
  temperature and its radius (surface area)
• A hotter star is more luminous than a cooler one
  of the same radius.
• A bigger star is more luminous than a smaller one
  of the same temperature.

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Surface Temperature
Surface temperature determines a star color.
The coolest stars are red, the hottest ones are
blue.
Betelgeuse has a temperature of 3,400 K, Sirius
9,400 K, the hottest stars up to 100,000 K.
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Star Clusters

• a. Open Clusters
• can contain from only a handful of stars to more
  than a hundred new stars being born in a single
  cloud of hydrogen gas and cosmic dust. The
  clusters are held together by gravity
•  
• b. Globular Clusters tightly packed balls of
  thousands or millions of old stars. Example a
  halo around the central hub of our Milky Way
  galaxy

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Stellar Masses
It is harder to measure stellar masses.
This procedure can only be applied to orbiting
objects Visual binary a resolved pair of stars
(Mizar) Eclipsing binary a pair orbiting in the
plane of our line of sight Spectroscopic binary
an object with regularly moving spectral lines or
with 2 line systems.
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Spectral Type
Stars are classified by assigning a spectral
type. The hottest stars are called spectral type
O, followed by B, A, F, G, K, M as the surface
temperature declines.
Oh Be A Fine Girl, Kiss Me
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The Hertzsprung-Russell Diagram
The diagram is a plot of stellar luminosities
against their surface temperatures.
Temperature increases leftward. Luminosity
increases upward.
H-R diagram
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Patterns in the H-R diagram
Main sequence location of the most stars (from
upper left to lower right corner) Luminosity
class V
Supergiant branch along the top (class I) Giant
branch just below the supergiants (class III)
White dwarfs near left corner (small size, high
temperature)
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HERTZSPRUNG_RUSSELL
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Groups of Stars by Mass
Low- and Intermediate-mass stars evolve into red
giants and ultimately become white dwarfs.
High-mass stars pass through a supergiant phase
and end their lives in violent explosions.
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Star Birth
A stars life begins in an interstellar
cloud. Star-forming clouds are dense and cold
(10-30 K). These clouds are called molecular
clouds.
The conditions in molecular clouds allow gravity
to overcome thermal pressure and begin the
gravitational collapse.
Gravitational contraction increases the clouds
thermal energy, which is radiated into
interstellar space as long-wavelength infrared
radiation.
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The Protostar Stage
A collapsing cloud fragment starts with angular
momentum, which increases the spin rate of the
fragment as it collapses.
As a result, a protostellar disk is formed. The
disk slows down the protostars rotation. The
rotation generates magnetic field. The field
lines transfer some of the angular momentum to
the disk. The magnetic field also generates a
strong protostellar wind.
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The Protostar Stage
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A Stars Infancy
A star is born when its core temperature exceeds
10 million K ? hydrogen fusion begins.
The stars interior stabilizes thermal energy
generated by fusion maintains the balance between
gravity and pressure.
The star becomes a main-sequence star.
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Low-Mass Star at Main-Sequence
Low-mass stars produce helium from hydrogen
The energy moves outward from the core through
random walk and convection.
The number of particles in the core reduces, the
core keeps shrinking, and the luminosity
increases over time.
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Red Giant Stage
When the core hydrogen depletes, nuclear fusion
STOPS The core with no energy source shrink
faster.
The stars outer layers expand and the luminosity
rises. The stars becomes a red giant through a
subgiant.
The radius increases 100 times. The luminosity
increases thousands times.
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Red Giant Stage
Why does the star grow bigger when the core is
when core shrinks?
The core is now made of helium, but the
surrounding layers contain plenty of
hydrogen. Gravity shrinks everything, so fusion
begins around the core (in a shell).
The fusion rate in the shell is higher than in
the core during the main-sequence stage. The
newly produced helium is added to the core.
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What Will Happen to Earth?
The Sun keeps increasing its luminosity. In 5
billion years from now the hydrogen burning will
stop in its core.
The Sun will then expand to a subgiant. It will
become 2?3 times brighter.
The Earths temperature will rise, the oceans
will be evaporated, the life may not survive. The
Earth may be destroyed, when the Sun becomes
planetary nebula.
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Supernova

• It is a explosive death of a massive star

. A neutron star is a small, powerful body left
behind when a massive star dies in a supernova
explosion.          A pulsar is formed when a
neutron star spins and its magnetic field
produces what we receive as a repeating,
clocklike energy signal of radio, light, X-ray
and gamma rays
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Supernova
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Nebula

• Nebulas are shadowy clouds of gas and dust. There
  are emission nebulas, reflection nebulas, dark
  nebulas, and planetary nebulas
•          Emission nebulas shine on their own.
  Ultraviolet light from nearby stars excites their
  hydrogen gas, causing it to fluoresce.
•          Reflection nebulas do not glow.
  Instead, tiny dust particles in the nebula
  reflect visible light from nearby stars.
•          Dark nebulas are cold dust and gas that
  absorb or scatter visible light from nearby
  stars. We know they are there when they block out
  the light visible coming from behind them.
•          Planetary nebulas are the gas and dust
  shells expelled by aging stars. They look like
  small bright disks. Although planetaries usually
  have very bright surfaces, their faint central
  stars often are difficult to detect without
  really large telescopes.
•  

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•     Dark nebulas are cold dust and gas       Dark
  nebulas are cold dust and gas that absorb or
  scatter visible light from nearby stars. We know
  they are there when they block out the light
  visible coming from behind them.
•          Planetary nebulas are the gas and dust
  shells expelled by aging stars. They look like
  small bright disks. Although planetaries usually
  have very bright surfaces, their faint central
  stars often are difficult to detect without
  really large telescopes.

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Nebulas

• Emission Nebula

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Reflection Nebula
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Planetary Nebula
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Dark Nebula
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White Dwarf

• A low and medium mass star (with mass less than
  about 8 times the mass of our Sun) will become a
  white dwarf. A typical white dwarf is about as
  massive as the Sun, yet only slightly bigger than
  the Earth. This makes white dwarfs one of the
  densest forms of matter.

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Death of High Mass Star

• Black Hole
• Neutron Star- small powerful body left after a
  massive star dies in supernova explosion
• Pulsar- forms from a neutron star spins and
  magnetic field produces energy signal