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How Are Stars Related?

Supernovas are only one way that stars die, and only certain stars are able to undergo a supernova. Remember the process that goes on inside a star? As the atoms fuse together, eventually the heavier elements such as iron are formed, and the core of the star is iron. By then the iron atoms are so massive that their force, or repulsion, is too strong to be pushed together to form other elements. What happens after that depends on the star's mass.
 
Stars, like humans, have a life cycle. Think about all of the events that occur in a human's lifetime. Now we will discuss how a star goes through its life cycle. We'll first start with an average mass star such as our sun.
 
This is what can be expected for our sun. All stars, including our own, are born in a nebula from compressed gas and dust as hydrogen begins to fuse to helium. This is when it enters what we call the Main Sequence of its life cycle, kind of like adulthood for us humans. After a few billion years in the main sequence, our sun will have fused all of its hydrogen into helium. The helium will begin to fuse into carbon, and the sun will begin to expand until it has reached Red Giant proportions. At the end of its Red Giant stage, much of the star’s material will be vented off into space, forming a planetary nebula.  All that will remain is the core, which is primarily carbon with some other elements, the heaviest probably being iron. That core will become a White Dwarf. Eventually all fusion will cease and the final remains of our sun will be a Black Dwarf.
 
Watch the Hubble telescope animation to see how a White Dwarf will eventually burn out and turn into a Black Dwarf.
 
However, a star that is 1.5 to 3 times more massive than our sun has a much different life cycle. It is still born in a nebula, from collapsing gas and dust. Its life will be shorter and its death will be more violent.
 
As you can see, stars of this size undergo a supernova. As the core is fused to iron, it will continue to gain energy and can even fuse into heavier elements. Eventually the force that causes the atoms to repel each other will become too strong (the heavier the atom, the stronger the force) and the star will explode. Elements much heavier than iron will fly out into space, forming a nebula from these materials. The remaining core of the star will collapse, becoming an EXTREMELY dense material called a Neutron Star. The matter that makes up a Neutron Star is so dense that one tablespoon of it would weigh several billion tons.
 
Watch the Colliding Binary Neutron Stars animation to see what happens when two neutron stars get too close to each other!
 

There is still one other route that a star could follow during its lifetime.

 
Watch the animation to see a black hole sucking in matter from a nearby star!
 

Scientists use what is called a Hertzsprung-Russell (H-R) Diagram to study star life cycles. The diagram is a graph of the luminosity (brightness) of stars plotted against their surface temperatures and/or color.

Click here to read more about H-R Diagrams and to do an Interactive Lab.

 

Analysis:

  1. What do you notice about the rate at which a sun-sized star dies compared to the rate at which a larger-sized star dies?
  2. What is the relationship between the mass of a star and the mass of the elements it can produce?
  3. Where is the sun found on an H-R Diagram?
 

Extension:

  • Want to learn more? Click here to do a fun WebQuest on Star Life Cycles.
  • Life Cycle Diagrams: Divide your friends into groups and have them diagram the life cycles of the stars described above— a sun-like star, a star 1.5 to 3 times the size of the sun (huge), and one 3 times or larger (giant).
 
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Updated October 24, 2008 by: Glen Westbroek

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