Download Star and Galaxies Chapter 13

Stars and Galaxies Galaxies
sStars
The Sun
Evolution of Stars
Galaxies and expanding
Universe
Stars
Constellations are grouping together of stars by
first Greeks/ Romans
They imagined constellations represented
mythological characters, animals or objects
Stars in constellations are not necessarily
clustered close together
88 constellations known today
Circumpolar Constellations
Earth rotates on its axis
When looking at the sky, the sky revolves around a
center point called the North Star (located near the
handle of the Little Dipper)
Constellations move around the North Star appearing
during parts of the year and disappearing below the
horizon during other times of year.
Some constellations appear year round that are near
the North Star
rAbsolute and Apparent Magnitude
Some stars
can appear very bright but are
actually are dim
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stars very close to earth.
Some stars appear dim but are very bright stars but are a great
distance from earth
Absolute Magnitude: Actual amount of light given off by a
star
Apparent Magnitude: is a measure of the light received on
earth
Sirius is the brightest star , but is a dim star that is 100 times
closer than Rigel (a star that is farther away). If both the same
distance from earth Rigel would be so much brighter
Measurement in Space
To find distance to stars, astronomers use Parallax
measurements
Using angles from earth on its revolution around the sun, they
can calculate distances to stars
Measurement in Space
• Units of distance of vast space is recorded in light years. It is
the distance light travels in one year (about 6 trillions miles in
one year)
Properties of Stars
• Color of Star indicates its temperature
• Red stars are relatively cool stars
• Blue/white stars are relative hot stars
• Yellow stars have medium temperatures
• When light passes through a prism, the
light is divided into its spectroscope
ranging from red, orange, yellow, green
blue, indigo and violet.
Spectroscope
• When light passes through a prism, the
light is divided into its spectroscope
ranging from red, orange, yellow, green
blue, indigo and violet. (red is cooler,
blue/violet is hottest)
• Star light is divided into its colors.
• As the light passes through the stars
atmosphere, there are black lines in
spectrograph caused by star’s atmosphere
absorbing some of its radiation depending
on the kinds of atoms in its atmosphere
Spectroscope
• Scientists knows the kind of black lines
associated with elements in the atmosphere and
can determine what the composition of the stars
atmosphere is by looking at those dark lines
Spectrograph of a star
The Sun
• Sun is our closet star made up of
layers of an atmosphere
• Energy is transfer to us through
radiation and convection
Sun’s Atmosphere
• Photosphere: lowest layer. Temp is about
6000°K, known as its surface, but is not smooth
• Chromosphere extends 1200 miles above
photosphere. Extends through a transition zone
up to 6000 miles above surface
• Corona is largest layer extends millions of miles
outward. Temperatures here is as high as 2
million degrees Kelvin
• Charged particles are emitted though corona
and move through space as solar wind
Sun’s Layers
Surface Features
• Sun spots: dark areas that are cooler
• Sunspots rotate as does the sun and can
follow the spots
• Rotates faster at equator, slower at poles
• Sunspots cycle every 10-11 years
• Prominences and Flares
• Intense magnetic fields associated with
sunspots might cause prominences (huge
arching columns of gas)
Surface Features
• Solar Flares: violent eruptions of gas near
sunspots shoot outward at great speeds
• CME’s are coronal mass ejections of
electrical charged gasses
• Can damage earths satellites, interfere
with radio and power distribution
equipment…. Produces auroras in
northern hemisphere
Average Star: The Sun
• Middle aged, absolute magnitude is about
average
• Shines yellow light
• Takes 8 minutes for light to reach earth
• It is unusual in fact it is found as a single star
(normally stars are in groups of 2 (binary
system)
• Star clusters: group of stars that have a
gravitation attraction to each other
• Appear fuzzy in sky. Pleiades star cluster is
obvious in winter skies .. Far from solar system
Evolution of Stars
Stars in the sky might appear similar, but are quite different
Hertzsprung and Russell observed characteristics where higher
temperature stars also have brighter absolute magnitudes
Developed a graph that showed this relationship called the H-R
diagram (Temperature along horizontal axis and brightness in
the vertical axis)
H-R Diagram
Main Sequence Stars
• Diagonal band that runs from upper left to lower right within
the H-R Diagram
• This gives a continuous flow of how a star is born and how it
becomes older. A main sequence star moves through the
band as it ages
• Upper left is hot bright stars, lower right is cool din stars
• Our sun is in the middle indicating middle age star
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90 % of all stars are a main sequence star
10% of stars aren’t part of Main Sequence
Some are hot but dim (lower left called white dwarfs)
Some are bright and cool (upper right called giants)
Dwarfs and Giants
Generating Energy
• Hydrogen fuses together to form Helium with great release
of energy.
• It releases electromagnetic energy in the form of light,
infrared, and ultraviolet light. Tiny fraction of light reaches
earth
• During fusion, 4 Hydrogen atoms fuse to form Helium where
small amount of mass is lost to energy in reaction (large
amount of energy is released)
• Fusion occurs in cores of all stars. In the core of stars the
temperatures are high enough to fuse atoms
Evolution of Stars
• As more and more H atoms are fused together, the fuel is
depleted
• Stars evolve depending on its original size
• Birth of Stars: begin as a large cloud of gas and dust called
nebula…. Gravity will pull gas and dust together which
eventually causes an unstable condition. It breaks into
smaller pieces that eventually become a new star
• Star is born when pieces move closer together, temperature
increases. When Core reaches 10 million degrees K, fusion
begins. Energy is released and star is born
Evolution of Star
• When stars begin the fusion process, they follow the Main
Sequence stars path
• When H is depleted, the balance between the gravity and
pressure no longer exists.
• Core contracts, temperatures increase, outer core expands
and cools and forms a late stage life cycle called a giant
When temperatures reach 100 million degrees K, helium
begins to fuse to form Carbon in giant’s core
The giant has expanded to an enormous size and its out layers
are much cooler. Our Sun will be a giant in about 5 billion
years
White Dwarfs
• When He is eventually used up, core
contracts inward and out layers escape
into space
• Leaves behind hot, dense core
• Our sun will become a white dwarf and
the sun at this stage is about size of Earth
• It will finally cool and stop giving off light
Supergiants and Supernovas
• If a star is 8 times more massive than out sun, the stages are
different
• Cores heat up to much higher temps, heavier elements fuse
together and star expands to supergiant.
• Eventually Fe forms in the core, and Fe can’t fuse to produce
energy
• Core collapses violently and shock waves travel outwards
• Outer portion of star explodes producing supernova
• Neutron stars: if collapsed core of supernova is between 1.4
to 3 times as massive as the sun, it will shrink to about 12
miles in diameter and a neutron star forms
• These are so dense that a teaspoon would weigh more than 600
million metric tons
Black Holes
• If remaining core of supernova is more than 3 times more
massive as the sun, probably nothing can stop the core’s
collapse. The core collapses to a point
• Gravity is so strong that nothing can escape from it, not even
light
• When light can’t escape, it is called black hole
• Black holes has an event horizon that if light enters it will
enter the black hole
• If an object does not cross the event horizon it will not be
drawn into the hole, rather orbit around black hole
Recycling Matter
• Star begins its life as a nebula, (parts of old stars that ejected
enormous amounts of matter during its lifetime)
• Star cores created during supernovas produce larger atoms of
carbon and iron
• These stars formed from supernovas and nebulas contain
heavier elements that could only have formed from recycled
stars
• Our sun isn’t large enough to produce Fe in atmosphere, so
the Fe had to have come from stars that died many Billions of
years ago
• Some elements condense to form planets. Our bodies contain
many atoms that were fused in the cores of ancient stars
• Are we are just recycled stars??????
Interactive H-R Diagram
• http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html
Galaxies and the Universe
• Galaxies: large group of stars, gas and
dust held together by gravity
• Earth and our solar system belong to the
Milky Way Galaxy which is made of a
trillion stars
• It is found close to 45 other galaxies
known as the Local Group
• These galaxies are separated by millions
of light years.
Types of Galaxies
• Sprial Galaxies: spiral arms that wind outward from center
• Milky Way is a spiral galaxy
• Can be normal or barred
Galaxy types
• Elliptical Galaxies: shaped like large 3 dimensional ellipse.
Looks like a football., some are round
• Some of these galaxies are huge fitting several Milky Ways
into one
Irregular Galaxies
• Galaxies that don’t fit into other two. Many different shapes
Milky Way Galaxy
• 100,000 light years across
• Sun is located 2/3 way from the center
• Takes 225 million years for sun to rotate around the
center
• Classified as normal spiral galaxy (recent studies show
think it might be barred)
• Milky Way is spread across the sky in a misty band
• Black hole found in center (2.5 million times more
massive as the sun)
Origin of Universe
• Steady state: universe has always existed, new
matter forms in center and expands outward
• Oscillating model: universe began to expand,
then contracted and oscillated between
expansion and contractions
• Big Bang Theory: universe began with a big
bang and has expanded ever since
Expansion of the Universe
• Doppler Effect: a shift of wavelengths (sound or
light waves) that reflect a change of pitch or
change of spectrograph
• As a train approaches you the wavelengths are
compressed and pitch is high, as it passes the
wavelengths are expanded and pitch is lower
• Light does same thing, rather a shift on the
spectrograph toward to red it is going away
from earth, and if shifted to blue it is
approaching earth
Doppler Shift
Big Bang Theory
• Occurred about 13.7 billion years ago
• Entire universe began expanding at the same time
• Hubble Telescope shows more than 1500 galaxies at
distances of more than 10 billion light years away.
• These galaxies could date back to when universe was no
more than a 1 billion old and are in different states of
developments
• Will the universe expand and gravity will begin to
contract back to a single point
• Whether the universe will continue to expands depend
on the dark energy that is causing the universe to
expand faster