Download Stars - Lauer Science

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All stars get their energy from FUSION
Fusion – combining of the nuclei of lighter
elements (hydrogen) to form a heavier element
(helium).
Fusion occurs in the core (middle) of a star.
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Apparent Magnitude
 Measure of how bright a star appears to be to an
observer on Earth.
 A low magnitude number means that the star is bright.
 The dimmest stars that can be seen with our eye have a
magnitude 6.
 The Sun has a magnitude of -27, by far the brightest
object in the sky.
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Luminosity
 actual brightness of a star and depends on its surface
area (size) and temperature.
 If two stars had the same temperature but different
sizes; the larger star would have a greater luminosity.
 If two stars were the same size but had different
temperatures, the hotter star would be more luminous.
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Absolute Magnitude
 Measure of how bright the star would be if all stars were
at the same distance from Earth.
 If you are moving the star closer to earth, it will be brighter.
 If you are moving the star farther from earth, it will be dimmer.
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All stars consist mostly of hydrogen and
helium
No two stars contain exactly the same
elements in the same amounts.
Astronomers use spectral analysis from a
spectroscope to determine a star’s
composition.
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A star’s mass is something that we cannot observe directly.
We can calculate what a stars mass might be on the basis of
other observations.
 it’s properties
 Gravitational influence on other objects.
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Stellar Masses
 The mass of all stars is expressed as multiples of the mass of the
sun.
 Sun’s mass is 1 solar mass.
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Size
 Stars vary more in size than in mass.
 Smallest stars are smaller than Earth.
 Largest star known is 2000 times larger than our sun.
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Range of color a star emits depends on its surface
temperature.
Surface Temperature (C)
Color
Prominent Elements in Spectrum
Above 30,000
Blue
Ionized Helium
9500 - 30,000
Bluish white
Neutral Helium
7000 - 9500
White
Metals, Hydrogen
6000 - 7000
Yellow White
Metals, Hydrogen
5200 - 6000
Yellow
Metals, Hydrogen
3900 - 5200
Orange
Metals, Hydrogen
Below 3900
Red
Titanium Oxide
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A Star is Born
 First…..
▪ All stars begin in a nebula.
▪ A nebula is a large cloud of gas and dust.
▪ Gravity pulls the gas and dust together to form a protostar.
▪ Protostar is the earliest stage of a star’s life.
 Then….
▪ The contracting gas and dust become so hot that nuclear fusion
starts
▪ Once fusion starts a star is “born.”
▪ Most stars become part of the main sequence at this point.
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Death of all Stars
 A star begins to die when it runs out of fuel (Hydrogen)
 Center of star shrinks and the outer part of the star expands becoming a
giant
 What death the star will have depends on the mass of the star
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Small Stars
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Small and medium sized stars end up as white dwarfs.
Outer layers keep getting bigger and eventually drift into space.
The blue-white hot core of the star is left.
The core is called a white dwarf.
Planetary nebula: glowing gas around a white dwarf.
White dwarf characteristics
 size of Earth and massive as the sun
 1 million times as dense as the sun.
 When a white dwarf stops glowing it is dead, and called a black dwarf.
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Dying giant star explodes.
The explosion is called a supernova
Material from the star can either create a new
nebula to form new stars or form neutron stars.
Neutron Characteristics
 Smaller and denser than white dwarfs.
 3 times the mass of the sun
 20 km in diameter (same size as a town here)
 PULSAR- spinning neutron star.
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The supergiant explodes in a supernova explosion.
This leaves behind a black hole.
Characteristics of a Black hole
 Nothing can escape from a black hole.
 We can detect black holes by
▪ X-rays coming from the hot gas going into the black hole.
▪ Effect of the black holes gravity on a nearby star.
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How long a star lives depends on its mass.
Small stars use up their Hydrogen slower than
large stars.
 Small stars can live for up to 200 billion years.
 Medium stars (sun) live for about 10 billion years.
 Larger stars can live for a few million years.
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© Sea & Sky
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© Sea & Sky
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Hertzsprung-Russell Diagram
Graph used to find out if temperature and
brightness of a star are related.
 Temperature plotted on the X-axis
 Brightness plotted on the Y-axis
 Most stars form a diagonal band called the main
sequence.
▪ Surface temperature increases as brightness increases.
▪ 90% of stars are main-sequence stars
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Activity:
Classifying Stars!!
Sun generates
energy in its core by
“cooking” hydrogen
to form helium.
This is called
nucleosynthesis.
Protons and Neutrons are conserved.
They fuse to form new elements.
Requires and releases immense heat
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The “cooking” of
elements is called
nuclear fusion
During nuclear
fusion, two or
more atoms of
one element
combine to form
one atom of a
different element
Protons and
Neutrons can
not be created
nor destroyed
It is an addition problem!
Time to Practice!!!
Hydrogen and some helium was made at the
beginning of the Universe (Big Bang).
• All other elements were made inside of stars, and
then spewed out into space by the supernova
explosions!
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• Low mass stars up to carbon
• High mass stars up to iron
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What about elements with atoms heavier than iron?
Such as Uranium, Gold, and so on?
 The heavy atoms are made during the supernova explosion
itself!
 There is so much energy during the explosion that iron
atoms can be forced together to form larger atoms.
Just before a
supernova, the inside
of the star has shells
of various elements.
X-ray picture of the “Cas-A”
supernova remnant. The
elements in this gas will
eventually be dispersed into
space, maybe to form new
stars, planets and people!
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Every substance gives off light when it gets hot
enough.
 Each element gives off its own special color. (emission spectrum)
 We use spectra to determine which elements make up
stars.
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Motion and distance is determined by the amount
of red shift.
 Red shift = moving away
 The farther the star the greater the red shift (Hubble’s Law)