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5 Types of galaxies1. Spiral = galaxy with tightly wound spiral arms; gas,
dust, hot bright stars, arms (new stars - metals) and obvious disk (old stars)
2. Elliptical = slightly elliptical to nearly circular; light gas & dust, no disk or arms, few hot bright stars. Old stars
3. Barred Spiral = spiral with a bright bar of gas through the center; elongated nucleus which arms originate. Old and new stars. 2x more common
4. Peculiar = fits none of the descriptions
5. Irregular = small, patchy, irregularly shaped galaxy. Rich in new and old stars.
Galaxy types : Deep survey imageCan you identify the type of galaxy labeled by each letter?
B=D=E=F=I =J =
• Galaxy Type: Spiral• Age: 5 billion year• 200 Billion other stars
130,000 Light YearsLight speed =186,000miles per second
Nuclear bulge: largest concentration of matter
Disk: flatter pat outside bulge
Arm: extend off bulge, our sun on Orion arm
You are here
Our Galaxy = Milky Way
universe
Galaxies: ex. milky way
Stellar regions:Ex. Orion’s arm
Planetary systems:Ex. Solar system
Small bodies:Asteroids, meteors, comets
Planets: Earth, Saturn…
Stars:The sun
The big bang: how the universe was formed
1. Scientists believe that their was a time when the density of matter was inconceivably high
2. All matter confined to a dense hot super-massive ball
3. 13.7 million years ago, a massive explosion occurred initiating the expansion of our universe.
4. The explosion generated lots of heat. As the universe cooled, helium and hydrogen were formed.
The big bang: The evidence
In 1929 Edwin Hubble discovered a red shift in the universe
Red shift = the lengthening of a wavelength due to its movement away from something. (red has a longer wavelength than the other visible colors)
The discovery of red shift showed that the universe
was moving apart.
The big bang
Primeval fireball: energetic, high frequency radiation (short waves)
Universe still expanding
Milky Way 5 billion years old
Humansobservecosmoses
Atoms afterH & Heforming
Plasma ofH & He
p+, e-, NØ
exist
Primeval fireball: energetic, high frequency radiation (short waves)
A stars life is a struggle between two forces…
1. Gravitational contraction = wants to make the star smaller
2. Internal pressure due to heat and nuclear fusion = wants to make the star bigger
The birth of stars: Step one
Step one = gravitational attraction within the nebula causes it to begin to contract.
Gravity > Inner Pressure
The birth of stars: step twoStep two = Formation of a protostar
Gravitational collapse allows for the accumulation of denser material in the center
Temperatures begin to increase• Material becomes more dense and particles collide.
1. Collisions = thermal energy2. More density = more collisions = more thermal energy
4. More thermal energy = increasing temperatures.
The birth of stars: step threeStep three = Nuclear Fusion begins
When a protosun become hot enough nuclear fusion will start to occur
Nuclear Fusion = the combining of two nuclei to form a larger element. This process releases energy, increases temp and increases pressure.
Gravity = Inner Pressure
Main sequence star = a star that is undergoing nuclear fusion a star will spend the majority of its lifetime here.
Gravity = Inner Pressure
The birth of stars: step threeStep three = Nuclear Fusion begins
There are three types of stars (based on mass)
1. Very Small Stars: red dwarfs
2. Low Mass Stars (our sun)
3. High Mass Stars (Betelgeuse)
Most of a stars life cycle is determined by its size (its mass)
A Star’s Life: Stellar evolution
Evolution of a Star
1. Nebula contracts due to gravity, protostar
2. Main sequenceOf high mass stars
2. Main sequenceOf low mass stars
3. Red giant
4. Red supergiant
5. Supernova6A. Blackhole
6B. Neutron star
4. He gone from core, outer layer escapes
5. Whitedwarf
Evolution of our Sun
Recyclingmatter
Life cycle of a very small star: Red Dwarf
Red Dwarf = a very small star. 1/10 to 1/2 the size of our sun. Very slow to non-existent rate of nuclear fusion Dies as an inert ball of helium, cooling an shrinking. Have the longest lifespan of any star (up to 100 billion yr.) may die as a helium white dwarf.
Proxima Centauri, the second closest star tothe Sun (4.1 light years), is a Red Dwarf.
Life cycle on low mass starsour sun
2. Main sequence star. Gravity = Internal pressure (core fusion)
3. Red giant. Internal pressure (shell fusion) > Gravity
4. Planetary nebula. Internal pressure > Gravity
1. Birth. Gravity > Internal pressure (fusion)
5. White dwarf. Gravity > Internal pressure
Life cycle on low mass stars: 3. Red GiantCore fusion stops
Main sequence star. Gravity = Internal pressure (fusion)
1. Fusion stops in the core. Star compresses under it’s own weight.
Gravity > Internal pressure
Life cycle of low mass stars: 3. Red Giantshell fusion begins
2. Compression = increases temperature, increase in density. Fusion begins again in the shell of the nucleus.
Core is contracting. Outer layers are expanding.
As outer layers expand, they cool and become a reddish color
Life cycle of low mass stars: Red giants
Red Giant = a low mass star whose core hydrogen has been depleted. • the star moves away from the main sequence• the increase in size is due to the expanding outer layers•The color is due to a decrease in temperature
As the red giant’s outer layers are expanding, it’s core is contracting
The contracting core = increase temp, increase in density Temperature is hot enough in the core of some red giants
that helium can form carbon!
Outer layer: internal pressure > gravity
Inner layer: gravity > internal pressure
Life cycle on low mass stars: 3. Red Giant Core fusion of carbon
Life cycle of low mass stars: 4. Planetary nebula
Outer layers continue expanding.Internal pressure > gravityStar explodes into a planetary nebula
Planetary nebula =An expanding shell of gas ejected from a low mass star toward the end of it’s life.
Life cycle of low mass stars: 5. White Dwarf
Core of the star, remains in the center of the nebula
White Dwarf = the earth size remnant of a red giant that cools slowly in the center of the nebula. Made of carbon.
Once again, gravity = pressure
Describe the lifecycle of a low mass star like the sun.
What is the heaviest element that loss mass stars can form?
Life cycle of High Mass stars:
2. Main sequence star. Gravity = Internal pressure (core fusion)
3. Red giant. Internal pressure (shell fusion) > Gravity
1. Birth. Gravity > Internal pressure (fusion)
4. Red Supergiant. Internal pressure (shell fusion) > Gravity
5. Supernova. Gravity > internal pressure
6a. Neutron Star. Gravity > internal pressure
6b. Black hole. Gravity > internal pressure
Life cycle of High Mass stars: the differences
1. Shorter Life Span - the bigger the star the faster they move through each stage.
2. Fusion of heavier elements - as outer layers expands, core contracts. Large mass = heavy = core shrinks.
High temperatures in the core allow for the fusion of carbon, neon, oxygen,silicon, iron.
Each stage is faster than the one before.
It always stops at iron.
Life cycle of High Mass stars: the differences
3. Size: Red Supergiants - due to the immense energy release as heavier elements are fused, the outer layer grow tremendously.
Betelgeuse (in Orion) is 800 times larger than our sun!
Life cycle of High Mass stars: 5. Supernova
All element greater than iron require energy, instead of releasing it.
When a Red Supergiant reaches this stage the core condenses to attempt to create the energy need.
The star collapses rapidly, creating a supernova
Supernova = the explosion of a massive star that occurs when its core runs out of nuclear fuel creating a gravitational collapse.
Life cycle of High Mass stars: Death
Option 1: 6a. Neutron Star
Neutron star = similar to white dwarfs but smaller and more massive. Created by the massive collapse of a red supergiant. Earth would be the size of a football field and weigh 100 million tonsHigh temperature but not very bright. Gravity > internal pressure
Option 2: 6b. Black hole
Black hole = objects smaller and more dense than Neutron stars. Created by massive Red Supergiants. Pull of gravity is so great that not even light can escape. Gravity >internal pressure
Properties of stars: Hertzsprung–Russell diagram
1. Size = mass 3. Temperature2. Luminosity (brightness) 4. Composition
(elements)
Our Sun6,000K (G)
High luminosityDue to size
O B A F G K M Star Type
Stars closer to death
Emission spectrum = a spectrum created by the emission of specific wavelengths of light. Colored lines on a black background
“Bright lights lab”
Absorption spectrum = the specific wavelengths of light absorbed by a gas. Dark lines on a color background.
Remember that good emitter = good absorbers
“Bright lights lab”
What is an emission spectrum?
What are old stars made of?
What are new stars made of?
“Bright lights lab”
•Astronomers study composition of stars by observing stellar spectra
Stellar spectra = unique emission spectrum produced by each star due to the elements present in the stars atmosphere.
“Bright lights lab”
We will be looking at the emission spectra of 6 elements:
Hydrogen (H -1) Neon (Ne - 10) Helium (He - 2) Krypton (Kr - 36)Oxygen (O - 8) Mercury (Hg -80)
Let’s take a look at their emission spectra
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