Unit 1: Origin of the Universe and Our Solar System

Physical Science

2^nd Semester 2024

Lesson 1: Origins of the Universe

• Scientists in the past were not able to readily observe evidence that allowed them to answer questions about the universe.

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• Technology has allowed scientists to:
• Gather evidence
• Develop theories about the origins of the universe
• Theorize about how the universe may or may not have evolved over time

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Lesson 1: Origins of the Universe

• In order to understand how the universe originated, we must first understand the Doppler Effect

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Lesson 1: What is the Doppler Effect ?

• The change in frequency of a wave due to the motion of an object.

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• You need to see it

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Ex:

• Doppler Radar
• Red Shift/Blue Shift

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Lesson 1: The Doppler Effect

• If the object is moving towards you, the waves are bunched closer together
• Sound waves have a higher pitch
• Light waves shift toward the blue end of the spectrum (extreme cases)

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Lesson 1: The Doppler Effect

• If the object is moving away from you, the waves are spread
• Sound waves have a lower pitch
• Light waves shift toward the red end of the spectrum (extreme cases)

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Lesson 1: The Doppler Effect

• What does this have to do with the origin of the universe?
• Can provide evidence if the universe is:
• Contracting (blue shift)
• Expanding (red shift)
• Stable (no change)
• The actual stars would not appear blue or red, however

Lesson 1: Absorption Spectrum

• Light from different gases absorb different wavelengths of light
• Absorption Spectrum
• Absorbed wavelengths appear as a black or missing section
• Scientists can use absorption spectrum to identify what stars are made from
• Red or Blue Shift shows up in the absorbed wavelengths of light
• Proves the universe is expanding

Part 1: Origin of the Universe Cosmic Microwave Background (CMB) Radiation

• Scientists were studying signals from the Milky Way Galaxy
• Heard unexplained humming noise
• Came from all directions in the galaxy with the same frequency
• Determined to be microwave radiation

Part 1: Origin of the Universe�What is radiation?

• Energy given off (emitted) in the form of electromagnetic waves
• Waves fell in the microwave range of the spectrum
• Scientist question:
• Where did this radiation come from?
• Why is it all around us?
• Why does it have the wavelength that it does?

Part 1: CMB

• Believed to be heat energy left over from the Big Bang
• As the universe expanded following the Big Bang, waves of energy were stretched as well
• Like the Doppler effect
• Stretched waves so far they now fall in the microwave range

Part 1: Origin of the Universe�Big Bang Theory

• If the universe is expanding, what did it look like billions of years ago?
• Size?
• Density?
• Energy?
• Heat?

Part 1: Big Bang Theory

• Big Bang Theory – most well supported theory for the origin of the universe
• Small, early universe was similar to conditions on the sun
• Plasma state of motion
• Incredibly hot and dense with high energy
• Unstable

Part 1: Big Bang Theory

• Eventually the universe exploded
• Heat and light exploded outward in all directions
• Occurred approximately 13 billion years ago
• Universe is expanding

Part 1: Origin of the Universe�Big Bang Theory

• When the universe expands, it does NOT mean the stars are moving away from us
• Distance between them grows

Part 1: Origin of the Universe�Evidence for the Big Bang Theory

Evidence for the Big Bang Theory:

1. Red shift – shows universe is expanding

2.CMB – even stronger evidence than Red Shift

• More directly associated with what the universe would have behaved like if it once existed as a tiny, singular point and then expanded suddenly

Part 2: Life Cycles of Stars�

• Stars - large, glowing balls of gas in space
• The sun is considered an average sized star

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Part 2: Life Cycle of Stars

Stars form from nebulas - a large cloud of gas and dust spread over a large volume

• Gravity pulls the dust and gas into a denser cloud
• Nebula heats up as it contracts
• Form early star
• Considered a star when nuclear fusion begins (occurs at high temperatures)

Part 2: Life Cycles of Stars

• Generate energy through nuclear fusion
• Nuclear Fusion - reaction in which atoms bond together to form a heavier nucleus, releasing energy in the process
• Indicators of energy change are light, heat, motion, or sound

Part 2: Life Cycle of Star

• Most stars are composed of Hydrogen
• Absorption Spectrum – Dark band appears around 678 Angstrom (Hydrogen) because that wavelength is being absorbed/used

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Part 2: Life Cycle of a Star

• Stars fuse hydrogen to form helium
• Hydrogen = main fuel of stars (can fuse other elements in the right conditions)

Part 2: Life Cycle of a Star

All elements in existence were created by fusion in stars

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Why are heavier elements created by heavy-mass stars?

* Nuclear fusion occurs at extremely high temps

* 5 million degrees C to fuse H

* 1 billion degrees C for Carbon

Part 2: Life Cycle of a Star

Fusion stabilizes star

Gravity pushes inward on stars

High mass = stronger force of gravity

Creates thermal force to push against gravity

More fusion = stronger thermal force

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These differences cause different life cycles in high and low mass stars

Part 2: Life Cycle of a Star

As it gets hotter, heavier elements can form

Fusion in stars can form elements up to Iron

All heavier elements formed when stars explode (supernova)

Part 2: Life Cycle of Stars

Early Star

• Continues contracting, increasing temperature and pressure
• Star is formed when it is so hot and dense that nuclear fusion occurs
• Joining nuclei together to form new elements

Part 2: Life Cycle of a Star (Adult Stars)

90% of a star’s life is spent on the main sequence

• Converting hydrogen to helium at a stable rate
• Force of gravity pushing inwards and thermal force pushing outwards are balanced (no change in size)
• Star’s mass determines place on the main sequence and how long it will stay there (relationship between brightness and mass)

Part 2: Life Cycle of Stars (Adult Stars)

When stars run out of hydrogen (fuel), they can’t do nuclear fusion (at least at the same rate)

• Not hot enough for other nuclei to fuse
• Less energy is produced
• Thermal energy and gravity are no longer stable
• Core starts to shrink

Part 2: Life Cycle of Stars (Death of a Star)

As the core shrinks, hydrogen from outside of the core undergoes nuclear fusion

• Energy is flowing out of the core causing outer regions to:
• Expand
• Cool (further from hot core)
• Star becomes a red giant

Part 2: Life Cycle of Stars (Death of a Star)

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• Meanwhile, collapsing core gets hotter
• Helium starts fusing
• Heavier elements form
• Star expands (thermal force in outer layers is stronger than gravity pushing in)
• Ultimately, star will die as it runs low on fuel (nuclei)

Part 2: Life Cycles of Stars�High Mass Stars vs. Low Mass Stars

• Following the Red Giant phase, the life cycle of a star depends on its mass
• High Mass vs. Low Mass stars – why the difference?
• Gravity is stronger on high mass stars

Part 2: Life Cycles of Stars�High Mass Stars vs. Low Mass Stars

• Gravity is stronger on high mass stars
• Pushes elements together more quickly, causing more fusion
• High mass stars do nuclear fusion more quickly
• Although they have more hydrogen to begin with, they run through it more quickly

Part 2: Life Cycles of Stars�High Mass Stars vs. Low Mass Stars

• High mass stars also produce heavier elements (like lead)
• More nuclear fusion = hotter
• Only high mass stars are hot enough for heavy elements to fuse
• 5 million degrees to fuse H
• 1 billion degrees to fuse C

Part 2: Life Cycle of a Star (Death of a Star)

Low/medium mass stars - become a white dwarf as its core continues to collapse

• Only the core is left
• Outer gases blow away
• No fusion
• Glows due to leftover energy

Part 2: Life of a Star (Death of a Star)

High Mass stars form a supernova when they collapse

Supernova - an extremely bright, violent explosion, produce enough energy to form elements heavier than iron

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Part 2: Life of a Star (Death of a Star)

Depending on the mass of the remaining core, the high mass star will become a:

Neutron star (lighter cores) or

Black hole (heavier cores) - surface gravity is so great that even electromagnetic waves traveling at the speed of light cannot escape it

Part 2: Life of a Star

Hertzsprung-Russell diagram – used to determine what type of star an object is

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Stars arranged by Temperature and Luminosity (High Temp is nearest the origin)

Part 2: Life of a Star

Shows a star’s color is determined by temperature (Blue = hottest)

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White Dwarf = Dim but hot

Red Giant = Bright but cool

Part 3: Patterns in the Solar System

• Planets that are closer to the sun are:
• Hotter
• More dense (made of metals and rocks)
• Called terrestrial planets
• Shorter orbit (closer)
• Smaller (more pressure from gravity)

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Part 3: Patterns in the Solar System

• Planets that are further from the sun are:
• Colder
• Less dense (cold enough that gases solidify)
• Called Jovian planets
• Longer orbit
• Large (mostly gaseous atmosphere, gases can’t escape)

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Part 4: Orbits of Celestial Bodies

• Gravity makes planets orbit the stars.

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• How does velocity change as distance increases?
• Further = slower (less gravitational pull)
• Orbits range from circular to elliptical

Part 4: Orbits of Celestial Bodies

• Circular Orbits
• The velocity of the planet/comet is in a straight line
• Gravity pulls the celestial body toward the star
• In a circular orbit, these two forces are balanced

Part 4: Orbits of Celestial Bodies

• Elliptical Orbits
• Pull of gravity and the velocity of the planet are not balanced
• Velocity is stronger than gravity, resulting in elliptical orbit
• Where is the planet moving the fastest?

Part 4: Orbits of Celestial Bodies

• Eccentricity – a measure that determines how much the orbit deviates from a perfect circle
• 0 = circular orbit
• 1 = elliptic orbit
• Greater than 1 = escape velocity
• Earth’s eccentricity = 0.0167
• How might eccentricity affect temperature? Speed? Other characteristics?