Star’s Life Cycle Goal: Create a diagram to help you understand this process Do Now: Our Sun is an average size star –will it ever become a Black Hole? Why or why not?

Creating your diagram Sketch the basic design as we go and add information when we come to each stage You have a big sheet of paper so that you will have enough room to add information at each step Fold your paper in fourths to help with spacing Use a pencil to sketch the circles, then add details later – don’t worry about colors at this point. Here’s a quick picture of what we will create

Summary of a Star’s “Life Cycle”

So, what is a star? A star is a really hot ball of gas, with hydrogen fusing into helium at its core. Stars spend the majority of their lives fusing hydrogen, and when the hydrogen fuel is gone, stars fuse helium into carbon. Throughout this whole process is that battle between gravity and gas pressure, known as equilibrium. It’s crucial to keep this battle in your mind when trying to understand how stars live and die. Let’s start the diagram!

Nebula

A cloud of gas and dust in space that comes together by gravity. Stars can form from the matter and energy in them. The nebula warms up, shrinks and becomes a proto-star (“pre” star)

Nebula Star

Main Sequence Star Nuclear reactions occur inside the star, light and heat is produced. Most of the stars life!! It’s destiny depends on it’s overall size. Larger stars become supergiants Smaller stars become red giants

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars

Let’s start with Smaller Stars Smaller stars last longer than the larger stars

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars

Vocab Review Red Giant – a large reddish star late in it’s life that converts helium into carbon or oxygen

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula

A planetary nebula forms when a star can no longer support itself by fusion reactions in its center. The gravity causes it to collapse and heat up. It lasts thousand years. The core remnant is uncovered and heats the now distant gases and causes them to glow. Despite the name, it has nothing to do with planets!

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf

Vocab Review White Dwarf – a small, dense star that remains after a red giant converts all of its helium into carbon or oxygen

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf Cools Black Dwarf

When a white dwarf cools to the point that it no longer emits significant heat or light. It takes tens to hundreds of billions of years for it to cool down entirely, and the Universe hasn't been around that long--the oldest stars are between 10 and 20 billion years old. Therefore there are no black dwarfs yet, but there will be in the future.

Now, Back to the Larger Stars… Supergiants can have masses from 10 to 70 solar masses and brightness from 30,000 up to hundreds of thousands times the solar luminosity. Because of their extreme masses they have short lifespans of only 10 to 50 million years and are only observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies.

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf Cools Black Dwarf

Vocab Review Red Supergiant - a large star late in its life cycle that converts its helium into iron

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf Cools Black Dwarf Super Nova

Vocab Review Supernova – a powerful explosion that occurs when a supergiant converts all of its helium into iron What causes a star to blow up? Gravity gives the supernova its energy. Once the core has gained so much mass that it cannot withstand its own weight, the core implodes

Supernova These have been observed! Supernova explosions are relatively rare events in our own galaxy, happening once a century or so on average. In 1987, there was a supernova explosion in the Large Magellanic Cloud, a companion galaxy to the Milky Way. Supernova 1987A, which is shown below:

Two pathways There are two possible results of the supernovas: Neutron Star or Black hole

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf Cools Black Dwarf Super Nova Neutron star Black Hole

Vocab Review Neutron Star – a small, dense dead star that can remain after a supernova

Vocab Review Black Hole - An extremely massive and dense object that can remain after a supernova These are so massive and dense that light cannot escape its gravity

Finish your diagram Add the title, “Star’s Life Cycle” Work with people at your table to make sure you wrote down the important information.

Nebula Star Super Giant Red Giant Large Stars Small/Medium Stars Planetary Nebula White Dwarf Cools Black Dwarf Super Nova Neutron star Black Hole Your Name Star’s “Life Cycle”

Summary of a Star’s “Life Cycle”

Add 0n Vocabulary Fusion This is the process where smaller atoms are combined to form larger atoms. On the sun, hydrogen atoms are fused or joined into a helium atoms. The by-product of this process is heat and light.

Vocabulary from your book In your own words, define the vocab (Geo Words) and add it to your glossary from p nebula: *luminosity *molecular cloud *supernova *neutron star *stellar black hole *nebula