Download Life cycle of low mass stars

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 galaxies
1. 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 scheme
Normal spirals
Galaxy examples
Galaxy types
Galaxy types : Deep survey image
Can you identify the
type of galaxy
labeled by each
letter?
B=
D=
E=
F=
I=
J=
Our Galaxy = Milky Way
• Galaxy Type: Spiral
• Age: 5 billion year
• 200 Billion other stars
Nuclear bulge:
largest
concentration
of matter
Disk: flatter
pat outside
bulge
Arm:
extend off
bulge,
our sun
on Orion
arm
You are here
130,000 Light Years
Light speed =186,000miles per second
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)
Primeval fireball: energetic, high frequency radiation (short waves)
p+, e-, NØ
exist
Plasma of
H & He
Atoms after
H & He
forming
Milky Way 5
billion years old
Humans
observe
cosmoses
Universe still expanding
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 two
Step 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 energy
2. 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 three
Step 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
The birth of stars: step three
Step three = Nuclear Fusion begins
Main sequence star = a star that is undergoing nuclear
fusion a star will spend the majority of its lifetime here.
Gravity = Inner Pressure
How is a star born?
(What are the first three stages?)
What is a main sequence star?
A Star’s Life: Stellar evolution
Most of a stars life cycle is determined by its size
(its mass)
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)
Evolution
of a Star
2. Main
sequence
Of high
mass
stars
1. Nebula
contracts
due to
gravity,
protostar
4. Red supergiant
5. Supernova
6A.
Black
hole
Recycling 6B. Neutron star
matter
4. He gone
from core,
outer layer
escapes
2. Main
sequence
Of low
mass
stars
5. White
dwarf
3. Red giant
Evolution of our Sun
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 to
the Sun (4.1 light years),
is a Red Dwarf.
Life cycle on low mass stars
our sun
1. Birth. Gravity > Internal pressure (fusion)
2. Main sequence star. Gravity = Internal pressure (core fusion)
3. Red giant. Internal pressure (shell fusion) > Gravity
4. Planetary nebula. Internal pressure > Gravity
5. White dwarf. Gravity > Internal pressure
Life cycle on low mass stars: 3. Red Giant
Core 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 Giant
shell 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?
Life cycle on low mass stars: 3. Red Giant
Core fusion of carbon
As the red giant’s outer layers are expanding, it’s core is
contracting
Outer layer: internal pressure > gravity
Inner layer: gravity > internal pressure
The contracting core = increase temp, increase in density
Temperature is hot enough in the core of some red giants
that helium can form carbon!
Life cycle of low mass stars:
4. Planetary nebula
Outer layers continue expanding.
Internal pressure > gravity
Star 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:
1. Birth. Gravity > Internal pressure (fusion)
2. Main sequence star. Gravity = Internal pressure (core fusion)
3. Red giant. Internal pressure (shell fusion) > Gravity
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?
4.
5.
3.
6b.
2.
1. birth
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 tons
High 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
2. Luminosity (brightness)
3. Temperature
4. Composition (elements)
Stars closer to death
High
luminosity
Due to size
Our Sun
6,000K (G)
O
B
A
FG K
M
Star Type
“Bright lights lab”
Emission spectrum = a spectrum created by the emission of
specific wavelengths of light. Colored lines on a black background
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)
Helium (He - 2)
Oxygen (O - 8)
Neon (Ne - 10)
Krypton (Kr - 36)
Mercury (Hg -80)
Let’s take a look at their emission spectra
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“Bright lights lab”
H
He
Ne
Hg
Please copy these onto the left side of your lab.