Astronomy: galaxies and stars

What are the five types of galaxies and their characteristics?

5 Types of galaxies

Galaxy = Large group of stars, planetary nebulae, interstellar gas & dust

Spiral galaxies

Elliptical galaxies

Barred Spiral galaxies

Irregular galaxies

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.

Hubble galaxy classification schemeNormal spirals

Galaxy examples

Galaxy types

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: Red shift

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)

The big bang

The big bang

STARS

A stars life is a struggle between two forces…

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

What is the one star in our solar system?

How was it formed?

What do we need in order to form a star?

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.

Why does temperature increase inside of a protostar?

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

How is a star born? (What are the first three stages?)

What is a main sequence star?

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

When our sun burns it supply of hydrogen, what will it become?

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!

What are three differences between Red Giants and Red Super giants?

Which one lives longer?

1. birth

2.

3.

4.5.

6b.

6a.

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.

What causes a supernova?

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”

Every element has a unique emission spectrum

“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”

What type of star do you think Vega is?

“Bright lights lab”

Where might you find this Nebula?

“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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are needed to see this picture.

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“Bright lights lab”

Hg

Ne

He

H

Please copy these onto the left side of your lab.