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Conversations with the Earth Tom Burbine [email protected] Quiz on Thursday. Sun Hertzsprung-Russell Diagram Death of stars. Main Sequence. Is not an evolutionary track Stars do not evolve on it Stars stop on the main sequence and spend most of their lives on it.

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quiz on thursday
Quiz on Thursday
  • Sun
  • Hertzsprung-Russell Diagram
  • Death of stars
main sequence
Main Sequence
  • Is not an evolutionary track
    • Stars do not evolve on it
  • Stars stop on the main sequence and spend most of their lives on it
sun ends it time on the main sequence
Sun ends it time on the main sequence

When the core hydrogen is depleted, nuclear fusion stops

The core pressure can no longer resist the crush of gravity

Core shrinks

why does the star expand
Why does the star expand?

The core is made of helium

The surrounding layers are made of hydrogen

slide8
And ..

Gravity shrinks the inert helium core and surrounding shell of hydrogen

The shell of hydrogen becomes hot for fusion

This is called hydrogen-shell burning

slide9
And …

The shell becomes so hot that its fusion rate is higher than the original core

This energy can not be transported fast enough to surface

Thermal pressure builds up and the star expands

slide10
And ..

More helium is being created

Mass of core increases

Increases its gravitational pull

Increasing the density and pressure of this region

slide12
When

When helium core reaches 100 million Kelvin,

Helium can fuse into a Carbon nucleus

helium flash
Helium Flash

The rising temperature in the core causes the helium fusion rate to rocket upward

Creates a lot of new energy

however
However

The core expands

Which pushes the hydrogen-burning shell outwards

Lowering the hydrogen-burning shell’s temperature

slide16
And

Less energy is produced

Star starts to contract

slide17
Now

In the core, Helium can fuse to become Carbon (and some Oxygen)

Star contracts

Helium fusion occurs in a shell surrounding the carbon core

Hydrogen shell can fuse above the Helium shell

Inner regions become hotter

Star expands

slide18

http://upload.wikimedia.org/wikipedia/commons/8/8d/Triple-Alpha_Process.pnghttp://upload.wikimedia.org/wikipedia/commons/8/8d/Triple-Alpha_Process.png

slide19
Some carbon fuses with He to form Oxygen

12C + 4He → 16O + gamma ray

Harder to fuse Oxygen with Helium to produce Neon

planetary nebulae
Planetary Nebulae

There is a carbon core and outer layers are ejected into space

The core is still hot and that ionizes the expanding gas

white dwarf
White Dwarf

The remaining core becomes a white dwarf

White dwarfs are usually composed of carbon and oxygen

Oxygen-neon-magnesium white dwarfs can also form

Helium white dwarfs can also form

high mass stars
High-Mass Stars

The importance of high-mass stars is that they make elements heavier than carbon

You need really hot temperatures which only occur with the weight of a very high-mass star

stages of high mass star s life
Stages of High-Mass Star’s Life

Similar to low-mass star’s

Except a high-mass star can continue to fuse elements

When the fusion ceases, the star becomes a supernova

Supernova is a huge explosion

fusion
Fusion

The temperatures of high-mass stars in its late-stage of life can reach temperatures above 600 million Kelvin

Can fuse Carbon and heavier elements

Helium Capture can also occur where Helium can be fused into heavy elements

deaths of stars
“Deaths” of Stars

White Dwarfs

Neutron Stars

Black Holes

white dwarfs
White Dwarfs

White Dwarfs is the core left over when a star can no longer undergo fusion

Most white dwarfs are composed of carbon and oxygen

Very dense

Some have densities of 3 million grams per cubic centimeter

A teaspoon of a white dwarf would weigh as much as an elephant

white dwarfs1
White Dwarfs

Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth

200,000 times as dense as the earth

white dwarfs2
White Dwarfs

Collapsing due to gravity

The collapse is stopped by electron degeneracy pressure

electron degeneracy pressure
Electron Degeneracy Pressure

No two electrons can occupy the same quantum state

the sun
The Sun

Will end up as a White Dwarf

neutron star
Neutron Star

Neutron stars are usually 10 kilometers acroos

But more massive than the Sun

Made almost entirely of neutrons

Electrons and protons have fused together

how do you make a neutron star
How do you make a neutron star?

Remnant of a Supernova

supernova
Supernova
  • A supernova is a stellar explosion.
  • Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months.
slide40

Type Ia Supernova

Type II Supernova

this stops with iron
This stops with Iron
  • Fusion of Iron with another element does not release energy
  • Fission of Iron does not release energy
  • So you keep on making Iron
initially
Initially
  • Gravity keeps on pulling the core together
  • The core keeps on shrinking
  • Electron degeneracy keeps the core together for awhile
slide45
Then
  • The iron core becomes too massive and collapses
  • The iron core becomes neutrons when protons and electrons fuse together
density of neutron star
Density of neutron star
  • You could take everybody on Earth and cram them into a volume the size of sugar cube
explosion
Explosion
  • The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core
  • 1044-46 Joules
  • Annual energy generation of Sun is 1034 Joules
how do we know there are neutron stars
How do we know there are neutron stars?
  • The identification of Pulsars
  • Pulsars give out pulses of radio waves at precise intervals
pulsars
Pulsars
  • Pulsars were found at the center of supernovae remnants
pulsars1
Pulsars
  • Pulsars were interpreted as rotating neutron stars
  • Only neutron stars could rotate that fast
  • Strong magnetic fields can beam radiation out
black holes
Black Holes
  • If a collapsing stellar core has a mass greater than 3 solar masses,
  • It becomes a black hole
black hole
Black Hole
  • After a supernova if all the outer mass of the star is not blown off
  • The mass falls back on the neutron star
  • The gravity causes the neutron star to keep contracting
black hole1
Black Hole
  • A black hole is a region where nothing can escape, even light.
event horizon
Event Horizon
  • Event Horizon is the boundary between the inside and outside of the Black Hole
  • Within the Event Horizon, the escape velocity is greater than the speed of light
  • Nothing can escape once it enters the Event Horizon
black hole sizes
Black Hole Sizes
  • A Black Hole with the mass of the Earth would have a radius of 0.009 meters
  • A Black Hole with the mass of the Sun would have a radius of 3 kilometers
slide60
No
  • Black Holes do not emit any light
  • So you must see them indirectly
  • You need to see the effects of their gravity
evidence
The white area is the core of a Galaxy

Inside the core there is a brown spiral-shaped disk.

It weighs a hundred thousand times as much as our Sun.

Evidence

http://helios.augustana.edu/~dr/img/ngc4261.jpg

evidence1
Evidence
  • Because it is rotating we can measure its radii and speed, and hence determine its mass.
  • This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun.
  • Gravity is about one million times as strong as on the sun.
  • Almost certainly this object is a black hole.
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