Before using please read all of the information down till the Explanations

Instructions:

    To begin the simulation click on the "Data Entry" button and the data screen will appear.  Enter in the three different variables for your star.  Enter in terms of solar constants.  Below are the constants for our sun.  You will enter in terms of these numbers.  Suggestions are provided to show you a good spreading of different stars and how their life lengths relate.

    Solar Mass= 1.989 x 10^30 kg

    Solar Core Temperature= 15 x 10^6 K

    Solar Core Density= 150,000 kg/m^3

!!Warning!!

            You must enter three values that are connected to each other.  All of these variables are related to each other on the Hertzsprung-Russell (H-R) diagram.  A good example of this diagram can be found in Kaufmann and Comins book Discovering the Universe on page 238.  If just arbitrary values are entered then the model will either crash or you won't receive an image of Hydrogen.

    Once you have enter in values press the "Evolve!" key.  This will start the animation and you will be able to see the changing percents of the elements and the closure of outward pressure and inward gravitational pull at the core.  If you wish to momentarily stop the animation then just hit "Pause".  If you wish to resume hit the "Evolve!" key again.

Key for Animation:

Green- the percentage of Heavier elements (primarily Carbon, Oxygen, and Nitrogen)

Blue- the percentage of Helium in the Star  The main sequence stars don't get hot enough to burn He in the model that I created

Red- the percentage of Hydrogen in the Star.  The main fuel source of the star.

    Once your star has completed its lifetime then the final stage window will appear.  After you have learned what happened to your star, you may wish to revisit the graphs on the previous screen.  Simply hit the "Graphs" button to return.

!!Tip!!

   If you enter in values that will create a small star compared to our Sun then the model will show that that star will continue to fuse elements for a long time.  If you want to skip ahead to see the final stage screen hit the "Fast Forward" button.  This only works for stars with 4 or less Solar masses.

   Time Steps:

        This the the most important part of the program.  In real-time the measurements for even a small depletion in Hydrogen would take several thousand years.  This program runs at a faster time interval and so can zoom along showing the effects of element fusion.  In order to make a proper scale I needed a sign post.  Since dwarfs live the longest I figured that they would be good.  I could then show the process being sped up as mass was added.  But the giant simulations lasted shorter than one calculations.  Then I guessed that the giants might be good markers.  However the dwarf simulation took several minutes even to see the slightest change.   

   I decided on the Sun as the proper time marker to see the longer low-mass stars and the faster high-mass stars.  The smallest star will take multiple minutes to complete.  That is why I added the "Fast Forward" button.  The simulation with a mass of 8 times that of our Sun will be much faster than that of the Sun.  And the largest star won't even show up on the screen except maybe a flash.  This shows the difference between stars that burn for longer periods of time and become white dwarfs with larger stars that burn faster and produce supernova and neutron stars.  This effect was for presentation only, and I added scalar values to certain variables to display these results.

Explanations:

I. Small stars burning all their fuel

            For stars that are under two solar masses and above 0.1 solar masses their fate is relatively calm and peaceful.  As the star produces energy it expands.  Once all the Hydrogen is used up the core begins to contract.  Pressure begins to build and the helium surrounding the core heats up driving the outer envelope outward.  The surface temperature begins to cool as it is forced outward.  The star now becomes a red giant.  They are so big that they leak gas into space at a rate that is one million faster than our sun currently does.  

    As the core contacts under its own gravitational pull the temperature begins to rise.  As the temperature approaches 100 million K the core begins to burn He and other heavier elements.  In stars that are between 2-4 solar masses the He burn increases gradually as the temperature rises with pressure.  However in the smallest stars the He burn begins suddenly in something called the helium flash.  In these low mass stars the core pressure must be extremely large in order to get temperature to burn He.  This collapse eventually leads to the creation of a degenerate gas.  At this point the core's temperature is increasing well over 100 million K.  The core can't expand and cool due to the pressure.  The He continues to burn at an incredible rate, hence the "flash".

    This flash and the resulting expansion from the increase in energy production will drive the star outward again.  The core cools and begins to collapse again.  This process continues as the star loses mass from ejecting it outward as the flashes occur every 300,000 years.  This ejected material expands and cools forming a space dust.  The core becomes exposed to the coldness of space and losses energy at an incredible rate.  The core actually ionizes the surrounding dust and causes it to glow into something called a planetary nebula.  

    The burned out core of these stars become white dwarfs.  This low mass hulks can't produce pressures that are sufficient to burn their heavier nuclear fuels.  They are fully compressed to the point that only degenerate gas is supporting the star against its own gravitational attraction.  Eventually this hulk will run out of fuel and become a black dwarf, a low mass object with a very high density.

        Like the low mass stars once their hydrogen fuel is used up these stars begin He burning.  However there is no He flash.  In fact these stars can create sufficient pressures to fuse even higher elements.  As temperatures approach 2.7 billion K in the stars core the radiated energy forces the star's outer layers further out than the giants I discussed earlier.  These giant masses are called super giants.

    As the size of elements being fused increases the rate that they are burned increases.  Eventually a star with 25 solar masses would burn thru all of its silicon supply in one day.  The last element created is iron.  Iron can no longer continue to fuse.  The enormous weight of the star must be supported by the brute strength of the iron degeneracy alone.  Eventually no even this can support so giant a star.  The core begins to collapse rapidly until it crashes in on itself causing a core bounce.  This bounce creates a giant shock wave that travels outward blowing off the outer layers of the star in a violent reaction.  This event is called a supernova.  Our star of twenty-five solar masses will blow off twenty-four solar masses worth of matter in such an explosion.  

    The remaining matter collapses to great density.  It forms lumps of materiel called neutron stars.  These small lumps of stuff are packed so tight that their escape velocity would be one half of the speed of light.   Using the conservation of momentum once such an amount of mass is compressed into such a high density, it begins to rotate extremely fast.  The period of rotation ranges from 0.2-1.5 seconds.  The Sun's rotation is a full month.  The speed of rotation and the size of its magnetic field create giant electric fields that act on protons and electrons that are found near the surface of the neutron star.  The result is a regular pulse of electric fields coming from the axis of rotation and that of the N-S orientation of the star's magnetic field.  These bodies are called pulsars.

    III.   Black Hole

Bibliography

1)    Seeds, Michael A.  Horizons Exploring the Universe fifth edition  Wadsworth Publishing Company  Belmont, CA  1997

2)    Kaufmann, III, William J., Comins, Neil F. Discovering the Universe fourth edition  W. H. Freeman and Company New York 1996

3)    Danby, J. M. Anthony, Kouzes, Richard, Whitney, Charles Astrophysics Simulations Consortium for Upper-level Physics Software  John Wiley and Sons, New York 1995

4)    Dr. Belloni, personal interviews, Spring 2000

5)    Dr. Cain, personal interviews, Spring 2000

6)    Dan Gerbatch,  personal interviews, Spring 2000

7)    Peter Campbell, personal interviews, Spring 2000

8)    Andrew Schoewe, personal interviews, Spring 2000

9)    Jay Holmes, personal interviews, Spring 2000