Download Unit 8 Chapter 30

Unit 8 Chapter 30
Stars, Galaxies and the
Universe
Section 1 Characteristics of Stars
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A star is a ball of gases that give off a tremendous amount of energy. As with our
“star” all star’s energy comes from nuclear fusion.
Another cool thing about stars is that they come in colors.
Analyzing Star Light
• Astronomers use a spectroscope to bend the light of the stars and look at the
properties of them.
Composition of Stars
• Hydrogen is the most abundant element
• Helium is the next
• Carbon, oxygen and nitrogen is the trace amounts
Temperature of Stars
• The surface temperature of the star will indicate the color. Hot stars are blue and
cooler stars are red. The in between are yellow or white.
The Size and Mass of Stars
• Sizes will vary as with any type of object. Our sun is an average size and mass.
Stellar Motion
There are two kinds of motion an object will have
Actual motion – going through space
Apparent motion – going across the sky
Apparent Motion
Apparent motion is the motion that the stars appear to make in the sky when in actuality
it is the earth that is moving.
Circumpolar stars
They are the stars that seem to revolve around the North Star (Polaris).
Because Polaris is near our axis point. Circumpolar stars are stars that move
around Polaris and are always visible in the Northern Hemisphere
Actual Motion
First, they move across the sky, which can be seen only for the closest stars. Second,
they may revolve around another star. Third, they either move away from or toward our
solar system.
Don’t forget – Red Shift, Blue Shift
Distances to Stars
Astronomical Unit – A.U.
Light Year
Parallax
Stellar Brightness
Brightness of Stars:
Around 120 BCE, a Greek astronomer named Hipparhus developed a system to
classify a stars brightness. He used about 850 of the stars that he studied.
The brighter stars were #1, dimmest were #6. Years later Ptolemy expanded
the scale to include 1000 stars.
Apparent Magnitude
Is how bright a star appears to be from the Earth. This depends on
how bright the star is and how far it is from the Earth. The scale is from 0 to
6, 0 being the brightest. If a star is brighter than a magnitude 0, you use a
negative value.
0
1
2
3
4
5
6
Brightest
Faintest
Each number is a multiple of 25 times higher than the one before. Example, A
magnitude 1 star is 25 times brighter than a magnitude 2 star. It is 25 X 25 or
625 times brighter than a magnitude 3 star.
Absolute Magnitude
How bright stars would appear if they were the same distance away
from Earth or 32.6 Light years away (10 parsecs). Our sun would be a 4.8,
average star, Rigel has an Absolute Magnitude of -6.4 which makes it appear
brighter than most stars.
Remember, all stars are not the same distance away, therefore, a faint star may
really be very bright if it were closer.
Variable Stars
Stars that change their brightness in cycles. The cycles can be short
(days) or long (years). This is caused by expansion (cooler/dimmer) or
contraction (hotter/brighter).
Section 2 Stellar Evolution
Because a typical star exists for billions of years, astronomers will never be able
to observe one star throughout its entire lifetime. Instead, they have developed
theories about the evolution of stars by studying stars in different stages of
development.
Classifying Stars
Stars are classified by luminosity, color and temperature.
Hertzsprung-Russell Diagram
Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris
Russell developed the diagram independently. This scale graphs all stars by
temperature and luminosity. See ESRT
Main Sequence:
Most of the stars in the galaxy fall into this category. They are very
stable stars that have long lives.
Luminosity
It is the actual brightness of a star. This depends on the Size and Temperature.
If sizes were equal, a hotter star would be more luminous than a cool one. If
temperature were the same, the larger ones would be more luminous.
Star Formation
It is believed that stars probably formed in similar ways. The theory is that a cloud of
dust (a nebula) contracts with most of the material going to the center to form a star.
The dust is mainly Hydrogen (99%) with other elements and compounds like silicon
carbide, graphite diamonds and nitrogen. The dust cloud most likely came from an
exploded star. As the cloud shrinks materials become hotter because of the compaction.
Protostars
A Protostar is a warm glowing mass.
The Birth of a Star
If the contraction continues hydrogen fusion may occur.
The Delicate Balancing Act
The Birth of a Star
• http://www.youtube.com/watch?v=S_nCIJ
nZDW8
The Main Sequence Stage
Stage one – new star that has used up about 5% Hydrogen
The second and longest stage in the life of a star is the mainsequence stage.
During this stage, energy continues to be generated in the core of the star as
hydrogen fuses into helium.
Stage 2: is the stable stage of the star
Leaving the Main Sequence
Stage 3: After a star is formed it continues hydrogen fusion. Eventually the
hydrogen is used up. This triggers fusion on the outside of the core. The star
expands when the core temperature becomes hot enough; it starts to fuse other
elements. The gases begin to blow away in bursts until a fierce hot core is left
(white dwarf).
Giant Stars
They are large cool stars with diameters 10 to 100 times larger than our
sun. Ex. Aldebaran and Arcturus
Red Giants:
When all the fuel (H) is used up the star starts to collapse again. This
gets the star hot again. Helium fusion begins. The star expands further
and is brighter than before.
Ex. Betelgeuse in Orion’s constellation
Super Giants
They are bright, hot stars whose diameter is more than 100 times larger than
our sun.
Ex. Blue-White Rigel and White-Yellow Canopus
The Final Stages of a Sun Like Star
In the evolution of a medium-sized star, fusion in the core will stop after
the helium atoms have fused into carbon and oxygen. With energy no
longer available from fusion, the star enters its final stages.
Planetary Nebula
Planetary Nebula is left (a glowing halo of gases that 18th century astronomers
thought they looked like disks of planets).
White Dwarfs
After a long while there is no more fuel left for the star, it collapses onto itself. It
becomes very small, earth size and only faintly glows until it becomes cold
and dark.
Novas and Super Novas
They are near the end of their lives as stars. If it flares up again, it becomes a
Nova (new star) and can burn for a while longer.
Super Nova: The center core of huge stars is mainly made up of heavy metals
(U, Pb, Fe, Ni). When all of the fuel is used up the collapse of these metals
is very rapid. The star can not contain all the material, it just EXPLODES.
The death takes millions of years, but when it gets to the core, it can take a
few weeks to a few months. This becomes the source material for new
stars/solar systems.
Pulsars
Neutron Stars
Neutron stars that are extremely
dense and small are formed
from super novas. This
causes a fast rotation. The
fast rotation and magnetic
fields causes radio waves to
be sent from the star in pulses.
Stars that contain about 8 or more
times the mass of the sun do
not become white dwarfs. After
a star explodes as a
supernova, the core may
contract into a very small but
incredibly dense ball of
neutrons, called a neutron star.
A single teaspoon of matter
from a neutron star would have
a mass of 2 × 1030 kilograms
(a 2 followed by 30 zeroes). A
neutron star that has more
mass than the sun may have a
diameter of only about 20 km
but may emit the same amount
of energy as 100,000 suns.
Neutron stars rotate very
rapidly.
Black Holes
When a really large neutron star collapses to the point where the mass is
infinitely small (all the mass of a star in a Point). The gravity is so strong that
light cannot escape. These are the most massive objects in existence. In
September 2000 the scientists discovered evidence concerning the existence of
a black hole in the center of our galaxy.
A nearby black hole, hurtling
like a cannonball through the
plane of our Milky Way, has
provided possibly the best
evidence yet that stellar-mass
black holes are made in
supernova explosions. This
black hole is streaking across
space at a rate of 400 000
kilometers per hour - 4 times
faster than the average
velocity of the stars in the
galactic neighborhood
Section 3: Star Groups
Most stars we see are at least 100 light years away. Most seem to be individual stars;
however, they really belong to larger groups.
Constellations
By using a star chart and observing carefully, you can identify many star groups that
form star patterns or regions. Although the stars that make up a pattern appear to be
close together, they are not all the same distance from Earth. In fact, they may be very
distant from one another.
Dividing up the Sky
In 1930, astronomers around the world agreed upon a standard set of 88
constellations. The stars of these constellations and the regions around them
divide the sky into sectors. Just as you can use a road map to locate a
particular town, you can use a map of the constellations to locate a particular
star.
Multiple Star Systems
Binary Stars are pairs of stars that revolve around each other.
There are some that are more than two.
Star Clusters
Sometimes, nebulas collapse to form groups of hundreds or
thousands of stars, called clusters. Globular clusters have a
spherical shape and can contain up to one million stars. An open
cluster is loosely shaped and rarely contains more than a few
hundred stars.
Omega Centauri
Galaxies
Galaxy:
Billions of stars rotating around each other or a central point
(black hole?). There are billions of galaxies out there.
Ours is called the Milky Way
Distances to Galaxies
By comparing the absolute magnitude to the apparent magnitude of stars,
Astronomers can judge the distances to other galaxies.
Types of Galaxies
Spiral galaxies are pin wheel shaped with
dense central core with spinning arms
extruding out from the core.
Elliptical are circular in shape with most stars in the
core. It does not have arms.
Irregular galaxies are the least common with no star pattern;
they are scattered randomly
The Milky Way
The Milky Way galaxy is a spiral galaxy in which the sun is one of hundreds of
billions of stars. Each star orbits around the center of the Milky Way galaxy. It
takes the sun about 225 million years to complete one orbit around the galaxy.
The Local Cluster is a group of 30 of the nearest galaxies
Quasars
Quasars are believed to be galaxies in early stages of development. They are
very bright, very far away. radio waves Tremendous come from them.
Section 4 The Big Bang Theory
Cosmology is the study of the universe. Cosmologists are the specialized
scientists who study how the universe was formed and when.
Hubble’s Observation
In 1929 Hubble discovered that ALL galaxies were RED SHIFTED. This meant
that all galaxies are moving apart. This is major proof for the big bang theory.
Measuring Red Shift
Hubble found that the spectra of galaxies, except for the few closest to Earth,
were shifted toward the red end of the spectrum. By examining the amount of
red shift, he determined the speed at which the galaxies were moving away
from Earth. Hubble found that the most distant galaxies showed the greatest
red shift and thus were moving away from Earth the fastest.
The Expanding Universe
By using Hubble's observations, astronomers were able to determine that the
universe was expanding.
A Theory Emerges
It is believed that all the matter in the universe started out in one small sphere.
There was an explosion and all the matter was sent outward. As it spread out,
the material was slowly transformed into the Universe we see today.
Cosmic Background Radiation
In 1964 background radiation is detected in space without a stellar source.
This could be the “sound” left over from the big bang. This also supports the
theory.
Ripples in Space
These ripples are irregularities in the cosmic background radiation, which were
caused by small fluctuations in the distribution of matter in the early universe.
The ripples are thought to indicate the first stages in the formation of the
universe's first galaxies.
A Universe of Surprises
Astronomers now think that the universe is made up of more mass and energy
than they can currently detect.
Dark Matter
23% of the universe is made up of a type of matter that does not give off light
but that has gravity that we can detect. Because this type of matter does not
give off light, it is called dark matter.
Dark Energy
Scientists think that it acts as a force that opposes gravity. Because of dark
energy, the universe is not only expanding, but the rate of expansion also
seems to be accelerating.