Stars and GalaxiesStars and Galaxies

BIGBIG Idea: Idea:

►The life cycle of every star is The life cycle of every star is determined by its determined by its massmass, , luminosityluminosity, , magnitudemagnitude, , temperaturetemperature, and , and compositioncomposition..

►Much of our information Much of our information about our galaxy and the about our galaxy and the universe comes from universe comes from ground-based observations ground-based observations

Hubble Space Telescope:Hubble Space Telescope:► In orbit since 1990.In orbit since 1990.►Takes extremely sharp Takes extremely sharp

images from space.images from space.►Hubble observations Hubble observations

have led to numerous have led to numerous scientific scientific breakthroughs, breakthroughs, including rate of including rate of expansion of the expansion of the universe.universe.

I. I. Characteristics of StarsCharacteristics of Stars

A.A. CompositionComposition and and TemperatureTemperature

► What are stars What are stars made of?made of?

►mostly mostly hydrogenhydrogen (H)(H)…about …about 73%73% of a star’s mass,of a star’s mass,

►approximately approximately 25% 25% heliumhelium (He) (He),,

►and the other and the other elements in small elements in small amounts: oxygen amounts: oxygen (O), carbon (C), (O), carbon (C), nitrogen (N), nitrogen (N), silicon (Si), silicon (Si), magnesium (Mg), magnesium (Mg), neon (Ne), iron neon (Ne), iron (Fe), sulfur (S)(Fe), sulfur (S)

Spectral Types:Spectral Types:

►SpectroscopeSpectroscope:: instrument instrument used to determine chemical used to determine chemical composition by separating composition by separating light into different colors light into different colors (wavelengths).(wavelengths).

Which stars are the hottest Which stars are the hottest stars?stars?

•Blue stars are the hottest

•Red stars are the coolest

B. Motion and Distance to B. Motion and Distance to the Starsthe Stars

►Doppler EffectDoppler Effect: : shift in wavelength shift in wavelength of light source moving toward or of light source moving toward or away from an observer.away from an observer.

Blue Shift:Blue Shift: shorter wavelengths, shorter wavelengths, stars moving stars moving towardstowards EarthEarth

Red Shift: Red Shift: longer wavelengths, longer wavelengths, stars moving stars moving away fromaway from Earth Earth

DistancesDistances between stars and between stars and Earth are measured in Earth are measured in light-light-yearsyears..

Light Year = Light Year = distance a light distance a light wave travels in one yearwave travels in one year

(one light year = (one light year = 236,750,151 times around 236,750,151 times around the Earth)the Earth)

C. Stellar MagnitudeC. Stellar Magnitude1. Apparent Magnitude:1. Apparent Magnitude: how bright a star how bright a star

appearsappears from Earth (depends from Earth (depends on light emitted and distance from Earth).on light emitted and distance from Earth).

LOWER NUMBER = BRIGHTER STAR

2. Absolute Magnitude:2. Absolute Magnitude: truetrue brightness of a star.brightness of a star.

How bright a star would appear How bright a star would appear if seen from the if seen from the same distancesame distance (32.6 light years) (32.6 light years)

Most stars fall between -5 and Most stars fall between -5 and +15+15

Our sun is +5: middle of the Our sun is +5: middle of the rangerange

3. Luminosity:3. Luminosity: energyenergy output output from the surface of a star per from the surface of a star per second; measured in watts.second; measured in watts.

►An Astronomer must know both An Astronomer must know both the star’s apparent magnitude the star’s apparent magnitude and how far away the star is.and how far away the star is.

►The brightness depends on both a The brightness depends on both a star’s luminosity and distance star’s luminosity and distance from Earth.from Earth.

D. Classification of StarsD. Classification of Stars►H-R DiagramH-R Diagram – shows relationship – shows relationship

between absolute magnitude and surface between absolute magnitude and surface temperature of star temperature of star the the brighterbrighter the star, the the star, the hotterhotter it is it is

►Stars have a finite lifetime Stars have a finite lifetime and evolve over timeand evolve over time

►The mass of a star controls The mass of a star controls its evolution, length of its evolution, length of lifetime, and ultimate fatelifetime, and ultimate fate

►As stars evolve, their As stars evolve, their positions on the positions on the Hertzsprung-Russell Hertzsprung-Russell diagram move…diagram move…

II. Stellar Evolution II. Stellar Evolution ““theorytheory””

►1. 1. NebulaNebula – stars – stars start out as start out as clouds of gas clouds of gas and dustand dust

70 % hydrogen70 % hydrogen 28 % helium28 % helium 2% heavier 2% heavier

elementselements

►Nebula in the Nebula in the

Constellation Constellation OrionOrion

►Star FormationStar Formation

►Gravity pulls particles together, Gravity pulls particles together, forming a sphereforming a sphere

►As density increases, gravitational As density increases, gravitational attraction increasesattraction increases

►Gravitational forces cause denser Gravitational forces cause denser regions of nebula to shrinkregions of nebula to shrink

►As regions become smaller, they As regions become smaller, they spin more rapidlyspin more rapidly

►Think of an Think of an ice skater…ice skater…

……as he/she as he/she pulls his or pulls his or her arms in her arms in closer, what closer, what happens to happens to the rate of the rate of the spin?the spin?

ProtostarProtostar – flattened disc of – flattened disc of matter with a central matter with a central

concentration (caused by concentration (caused by shrinking, spinning region)shrinking, spinning region)

►Pressure and density build within the Pressure and density build within the protostar’s center, causing temperature to protostar’s center, causing temperature to riserise

►Gas is so hot it becomes Gas is so hot it becomes plasmaplasma (a fourth (a fourth state of matter)state of matter)

►Temperature continues to increase until it Temperature continues to increase until it reaches 10,000,000reaches 10,000,000ººC C

►At this temperature nuclear fusion beginsAt this temperature nuclear fusion begins►A star is born !A star is born !

2. 2. Main Sequence StarsMain Sequence Stars – –

► The second and The second and longest longest stage in stage in the life of a starthe life of a star

►MostMost stars fall stars fall within the main within the main sequence bandsequence band

►Our sun is a Our sun is a MainMain Sequence StarSequence Star

►During this During this main sequence main sequence stagestage, energy is generated in the , energy is generated in the core of the star as core of the star as hydrogen hydrogen atoms fuse to become atoms fuse to become heliumhelium atomsatoms

►Fusion releases huge amounts of Fusion releases huge amounts of radiant energyradiant energy

3. 3. GiantsGiants – very large cool bright – very large cool bright starstar

►Hydrogen starts to Hydrogen starts to run out and the star run out and the star expands greatly.expands greatly.

► Super Giants are Super Giants are very big Giantsvery big Giants

►Our sun is 5 billion Our sun is 5 billion years old and has years old and has only converted 5 % only converted 5 % of its hydrogen to of its hydrogen to helium.helium.

A Giant is 10x bigger than the Sun and a Supergiant is 100x bigger

4. 4. White DwarfWhite Dwarf – final stage of a – final stage of a starstar

► Planetary Planetary NebulaNebula – – expanding shell of expanding shell of gases shed by a gases shed by a dying stardying star

►Gravity causes the last of the matter Gravity causes the last of the matter in the star to collapse inwardin the star to collapse inward

►What remains is a hot, dense core of What remains is a hot, dense core of matter…a matter…a WHITE DWARFWHITE DWARF

►White dwarfs shine for billions of White dwarfs shine for billions of years before they cool completelyyears before they cool completely

►As white dwarfs cool they become As white dwarfs cool they become fainter and fainter…fainter and fainter…

►When they no longer emit energy, When they no longer emit energy, they become a they become a blackblack dwarf, a dead , a dead starstar

Black dwarfs probably do not Black dwarfs probably do not yet exist…yet exist…

WHY?WHY?

NovasNovas – explosions that occur as a – explosions that occur as a white dwarf coolswhite dwarf cools

►SupernovaSupernova – – star that has star that has such a such a tremendous tremendous explosion that it explosion that it blows itself apart.blows itself apart.

Neutron StarsNeutron Stars – small but incredibly – small but incredibly dense ball of neutrons, formed from the dense ball of neutrons, formed from the

collapsed core of a supernova.collapsed core of a supernova.

►One teaspoon of One teaspoon of material from a material from a neutron star would neutron star would weigh 100 million weigh 100 million tons on Earth.tons on Earth.

Black HolesBlack Holes – hole left by the collapse – hole left by the collapse of of a supernova.a supernova.

►The gravity of a black hole is so great The gravity of a black hole is so great that not even light can escape from it.that not even light can escape from it.

III. Star GroupsIII. Star Groups

A. Constellations:A. Constellations: patterns of patterns of stars in the skystars in the sky

there are 88 different there are 88 different patterns of stars recognized.patterns of stars recognized.

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B.B. GalaxiesGalaxies

►A A galaxygalaxy is a large group of is a large group of stars bound by gravity.stars bound by gravity.

typically 100,000 light-years typically 100,000 light-years wide wide

contain contain billionsbillions of stars of stars

Types of GalaxiesTypes of Galaxies1. Spiral:1. Spiral: central mass (nucleus) of central mass (nucleus) of

bright stars with flat arms that bright stars with flat arms that spiral around it spiral around it

arms contain millions of young arms contain millions of young stars, gas, and dust.stars, gas, and dust.

Top View Side View

2. Elliptical:2. Elliptical: nearly spherical with nearly spherical with very bright centers; no spiral armsvery bright centers; no spiral armsNo young stars, dust, or gasNo young stars, dust, or gas

3. Irregular:3. Irregular: no particular shape. no particular shape. small and faint, with little small and faint, with little

gravitational attraction to gravitational attraction to organize it into a shapeorganize it into a shape

may also be unorganized due to may also be unorganized due to the collision with another galaxythe collision with another galaxy

What What typetype of galaxy do of galaxy do we live in?we live in?

The Milky WayThe Milky Way-Spiral galaxy in which our solar system is located

-100,000 light-years wide

- The sun is 30,000 light- years from the center

- The sun revolves around the center at 250 km/sec

- It takes 200 million years to make one revolution.

IV. FORMATION OF THE IV. FORMATION OF THE UNIVERSEUNIVERSE

►The The Big Bang TheoryBig Bang Theory: most widely : most widely accepted theory explaining the formation of accepted theory explaining the formation of the universe.the universe. All matter and energy in the universe was All matter and energy in the universe was

once concentrated in a very small, very once concentrated in a very small, very hot, very dense volumehot, very dense volume

12-15 billion years ago, the “big bang” 12-15 billion years ago, the “big bang” occurredoccurred

Matter and energy were propelled outward Matter and energy were propelled outward in all directionsin all directions

The universe began to E X P A N D…The universe began to E X P A N D…

As matter and energy moved As matter and energy moved outward, the force of gravity had an outward, the force of gravity had an effecteffect

Matter began to condense, forming Matter began to condense, forming the galaxiesthe galaxies

The galaxies continued to move The galaxies continued to move outward, as they continue to do outward, as they continue to do today…today…

V. The SunV. The Sun►There is nothing special about the Sun…There is nothing special about the Sun…

It’s just close enough to Earth to give us It’s just close enough to Earth to give us light and warmthlight and warmth

The Sun is similar to most other stars in The Sun is similar to most other stars in our galaxy:our galaxy:►A large ball of gas made mostly of A large ball of gas made mostly of hydrogen hydrogen and and heliumhelium held together held together by gravity.by gravity.

►The Sun is The Sun is 300,000 300,000 times larger than Earthtimes larger than Earth

A. Structure of the SunA. Structure of the Sun1. Core1. Core

The The veryvery hot (15,000,000 hot (15,000,000ººC) C) gaseous centergaseous center

This is where nuclear This is where nuclear fusionfusion occursoccurs

FUSIONFUSION is how the Sun makes its is how the Sun makes its energy!energy!

Hydrogen

Hydrogen

Helium

2. The Inner Zones2. The Inner Zones

a. a. Radiative ZoneRadiative Zone►Zone surrounding the coreZone surrounding the core►Heat energy moves by radiationHeat energy moves by radiation

b. b. Convective ZoneConvective Zone►Around the radiative zone Around the radiative zone ►Heat energy moves by Heat energy moves by convectionconvection

3. The Sun’s Atmosphere 3. The Sun’s Atmosphere (uppermost region of solar (uppermost region of solar gases)gases)

a. a. PhotospherePhotosphere:: “light sphere”“light sphere”

►visible visible surface of surface of the Sunthe Sun

►what we seewhat we see

b. b. Chromosphere:Chromosphere: “color “color sphere”sphere”

thin layerthin layerseems to glow with seems to glow with reddishreddish lightlight

►c. c. CoronaCorona:: “crown” “crown” outermost layer of Sun’s outermost layer of Sun’s

atmosphereatmosphere cannot be seen with naked eye, cannot be seen with naked eye,

except during TOTAL solar eclipseexcept during TOTAL solar eclipse huge cloud of gas that keeps the huge cloud of gas that keeps the

atomic particles from the surface atomic particles from the surface from escaping into spacefrom escaping into space

►Solar windsSolar winds the corona does not have a the corona does not have a

defined edgedefined edge gas flows outward from the gas flows outward from the

corona at high speeds, forming corona at high speeds, forming solar windssolar winds

electrically charged atomic electrically charged atomic particles stream into space particles stream into space through holes in the coronathrough holes in the corona

flow to distant parts of solar flow to distant parts of solar systemsystem

B. Solar ActivityB. Solar Activity

1. 1. Sunspots: Sunspots: cooledcooled regions within regions within the the photosphere photosphere

►Appear Appear darkerdarker than the areas than the areas around themaround them

2. 2. Prominences:Prominences: disturbances in solar atmospheredisturbances in solar atmosphere great clouds of glowing gasesgreat clouds of glowing gases huge arches that reach high above huge arches that reach high above

Sun’s surfaceSun’s surface

3. 3. Solar Flares:Solar Flares: sudden violent sudden violent eruptions of electrically charged atomic eruptions of electrically charged atomic

particles. particles.

4. 4. Auroras Auroras (aka “Northern Lights” or (aka “Northern Lights” or “Southern Lights”):“Southern Lights”):

►Magnetic storms in the Earth’s upper atmosphereMagnetic storms in the Earth’s upper atmosphere► Solar winds attracted to Earth’s magnetic poles Solar winds attracted to Earth’s magnetic poles

by the Earth’s magnetosphere (space around by the Earth’s magnetosphere (space around Earth that contains a magnetic field)Earth that contains a magnetic field)

► Electrically charged particles strike gas Electrically charged particles strike gas molecules in the upper atmospheremolecules in the upper atmosphere

►Green, red, blue, or violet sheets of light are Green, red, blue, or violet sheets of light are producedproduced

► Visible about 5 times per year, usually in polar Visible about 5 times per year, usually in polar regionsregions

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VI. Our Solar SystemVI. Our Solar System

►How many stars do we have in our How many stars do we have in our Solar System?Solar System?

►What bodies make up our Solar What bodies make up our Solar System?System?

Formation of the Solar Formation of the Solar SystemSystem

►Solar system = the Sun and the Solar system = the Sun and the planets and other bodies that travel planets and other bodies that travel around the Sunaround the Sun

►Solar Nebular TheorySolar Nebular Theory:: our best our best current idea for the origin of the solar current idea for the origin of the solar system…system…

►Big Bang spread matter throughout Big Bang spread matter throughout universeuniverse

►Some matter gathered into clouds of Some matter gathered into clouds of dust and gasdust and gas

►Cloud of gas and dust that eventually Cloud of gas and dust that eventually developed into our solar system is developed into our solar system is called the ‘SOLAR NEBULA’called the ‘SOLAR NEBULA’

►Solar nebula was larger than our solar Solar nebula was larger than our solar system is nowsystem is now

►Heat and pressure from force of Heat and pressure from force of gravity caused center of solar nebula gravity caused center of solar nebula to become hotter and denserto become hotter and denser

►While the Sun was forming in the While the Sun was forming in the center of the solar nebula, planets center of the solar nebula, planets were forming in the outer regionswere forming in the outer regions

►PlanetesimalsPlanetesimals (small bodies of (small bodies of matter within the solar nebula) joined matter within the solar nebula) joined together through collisions and the together through collisions and the force of gravity to form larger bodies force of gravity to form larger bodies called protoplanetscalled protoplanets

►ProtoplanetsProtoplanets then condensed into then condensed into existing planets and moons…existing planets and moons…

►The four protoplanets closest to The four protoplanets closest to the Sun became:the Sun became:

►MercuryMercury►VenusVenus►EarthEarth►MarsMars

►The The next next four protoplanets four protoplanets became:became:

►JupiterJupiter►SaturnSaturn►UranusUranus►NeptuneNeptune