# Presentation: 112231

## Element Building in Small Stars

***Life Cycles of Stars, Part I***

- Elements 2002 Workshop

**Notes:**
Imagine Life Cycle Poster Image

## Twinkle, Twinkle, Little Star ...

***Twinkle, Twinkle, Little Star ...***

## How I Wonder What You Are ...	

- Stars have
- Different colors
- Which indicate different temperatures
- Different masses
- Different sizes
- The bigger it is, the hotter and the faster a star burns its life away.

**Notes:**
By looking at previous slide, audience should determine that stars have different colors, and deduce that this means different temperatures..
They won’t be able to tell from the image that stars are of different sizes and masses, but they may be able to deduce that from the different temps. 
With different masses and sizes, make analogy that some people are tall and others are short.

## Stellar Nursery

**Space is filled with the stuff to make stars.**

## Stars start from clouds

**Clouds provide the gas and dust from which stars form. **

**Rather: Irregular Grains **
**Of Carbon or Silicon**

## Collapse to Protostar

- Stars begin with slow accumulation of gas and dust.
- Gravitational attraction of Clumps attracts more material.
- Contraction causes Temperature and Pressure to slowly increase.

**Notes:**
Protostars grow on the principle that “The rich get richer”.  As the clump grows, the gravitational force it exerts increases, and thus is able to grow more.
The equation gives the gravitational force exerted by mass m1 on mass ms.  As the mass of m1 increases, the force it exerts increases.

## Nuclear Fusion !

- At 15 million degrees Kelvin in the center of the star, fusion ignites !
-   4 (**1**H) --> **4**He + 2 e+ + 2 neutrinos + energy
- Where does the energy come from ?
- Mass of four **1**H > Mass of one **4**He

- E = mc2

**Notes:**
Be sure audience members understand what the symbols mean.  Especially that the superscripts for H and He are the atomic weights.

The energy comes from the slight difference in mass between four H atoms and one He atom.  This excess mass gets converted to energy via Einstein’s famous equation.

## Fusion done in pairs

- Proton-Proton Chain:
- 	2 x (**1**H + **1**H--> **2**H + e+ + neutrino)
- 	2 x (**2**H + **1**H --> 3He + energy)
- 	     3He + 3He --> 4He + **1**H + **1**H
- The net effect is
- 4 (**1**H) --> **4**He + 2 e+ + 2 neutrinos + energy

**Notes:**
This slide provides the details on how H fuses into Helium.  Note that it takes a few steps because it occurs only in pairs.

## Fusion by the Numbers

- 4 (**1**H) --> **4**He + 2 e+ + 2 neutrinos + energy
-         Mass of 4 **1**H 	= 4 x 1.00794 amu
- 		= 4.03176 amu
-       Mass of 1 **4**He 	= 4.002602 amu
- Difference in mass = 0.029158 amu
- 		= 4.84 x 10 -29 kg.
-  E = mc2 = (4.84 x 10 -29 kg)(3 x 108 m/s)2
- E = 4.4 x 10 -12 J

**Notes:**
This slide is optional, depending on the mathematical background of the audience, and how much detail they need to see.
Here we explicitly show the difference in mass between the H and He, and how it gets converted to energy.  Note that 1 amu = 1.66053 x 10-24 g

## How much Energy

- 4 (**1**H) --> **4**He + 2 e+ + 2 neutrinos + energy
- Energy released = 25 MeV
- 		= 4 x 10 -12 Joules
- 		= 1 x 10 -15 Calories
- But the sun does this 1038 times a second !
- Sun has 1056 H atoms to burn !

**Notes:**
1 MeV is the voltage necessary to move 1 million electrons through 1 volt

Re- 1 ev = 1.6 x 10-19 J.  1 cal = 4.184 J
The kinetic energy of a 90 m/hr fastball is 0.5*(0.145 kg)*(40m/s)^2 = 116 J
The “Calories” given in the slide are kcal, the same as used on food labels.

We know the rate at which the sun consumes H because we can measure its energy output.  We know how many H atoms it has from knowing the sun’s mass (2 x 1030 kg). 

## Periodic Table

## A Balancing Act

- Energy released from nuclear fusion counter-acts inward force of gravity.
- Throughout its life, these two forces determine the stages of a star’s life.

**Notes:**
This is an important principle which governs the life stages of a star.

## New Stars are not quiet !

- Expulsion of gas from a young binary star system

## All Types of Stars

- Oh Big And Ferocious Gorilla, Kill My Roommate Next Saturday !

- Oh! Be a Fine Girl - Kiss Me !

- Oh! Be a Fine Girl - Kiss Me Right Now Sweetheart !

## Reprise: the Life Cycle

- Sun-like Stars

- Massive Stars

**Notes:**
Stars are either low mass or high mass.  Their mass determines their fate.
One might note that stars are not quiescent even during the time they steadily fuse Hydrogen.  For example, our own sun is very active.

## Main Sequence - the Prime of Life

- Elements dispersed via Stellar Winds
- Solar Wind (1-10 particles/cm3)
- Emitted from solar corona at speeds ranging from 300-800 km/s

-  Consists of Electrons & Ions
-  95% H, 4% He
-  1% other: C, N, O, Ne, Mg, Si

- Apollo Solar Composition Experiment

## The beginning of the end: Red Giants

## Red Giants

- After Hydrogen is exhausted in core,
- Core collapses, releasing energy to the outer layers
- Outer layers expand
- Meanwhile, as core collapses,
- Increasing Temperature and Pressure ...

## More Fusion !

- At 100 million degrees Celsius, Helium fuses:
- 3 (**4**He) --> **12**C + energy
- (Only 7.3 MeV produced)
- Energy sustains the expanded outer layers
- of the Red Giant

**Notes:**
Note that fusion of He requires a much hotter temperature than fusion of H.

## Summary of Element Production in Small Stars

## The end for solar type stars

***The end for solar type stars***

**Planetary Nebulae**

- After Helium exhausted, outer layers of star expelled

## White dwarfs

- At center of Planetary Nebula lies a
- 	White Dwarf.
- Size of the Earth with Mass of the Sun 	“A ton per teaspoon”
- Inward force of gravity balanced by repulsive force of electrons.

**Notes:**
Basic characteristics of white dwarfs: about the size of the earth, with a mass of about the sun. 1 million g/cm3 = “1 ton/teaspoon”
White Dwarfs are stable because inward force of gravity is balanced by the repulsive force of the electrons.

## Novae from White Dwarfs

- When in a close binary system,
- White dwarf accumulates gas from stellar companion.

-  Material accumulates until H fusion occurs (explosively !)
- Brightens by ~ 10,000x, fading over 30+ days
-  Ejects He, C, N, Ne, O

**Notes:**
Novae from White Dwarfs give us some quantities of He and heavier elements, but not as large as when the white dwarf itself explodes.

## Elements from Small Stars

**Notes:**
This summarizes the elements we get from small stars.

## Materials for Life Cycles of Stars

- Materials on the Life Cycles of Stars, are available on the Imagine the Universe! web site at:
- http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/stars.html