Get into a group of 4 1 person in the group signs out a laptop. Log in. Open this power point in your class folder Studentshared/science/11x3

You will today make a poster showing the life cycle of stars. Everyone makes their own. There are 3 possible life cycles. In your group make sure that you are showing all 3 lifecycles.

The Life Cycle of Stars

Stars form from clouds of Hydrogen gas...

The force of gravity between all the atoms will result in the cloud slowly contracting towards its centre. Press to play Gravity Animation Complete

The result will be a dense ball of hydrogen, called a Protostar. As it contracts, the Gravitational Potential Energy of the gas is converted into Heat, warming the Protostar.

If the Protostar has enough mass, the temperature and density at the core will be enough for Fusion to begin, with Hydrogen atoms combining to form Helium. Press to play He H H Animation Complete

The process of Fusion in the core generates heat, which further warms the core and also warms up the outer layer of Hydrogen. Once Fusion starts the Protostar becomes a Main Sequence Star. Press to play He H H Animation Complete

Over time, because of the Fusion process, the core becomes more and more composed of Helium rather than Hydrogen. The outer layer of the star will still be Hydrogen. Press to play He H H Animation Complete

As further time passes, the Hydrogen begins to run out. The star will expand to become a Red Giant or Red Super Giant and Fusion will begin to generate heavier elements than Helium.

What happens next depends on the mass of the star ….

If the star is small (up to 1.5 times the mass of our sun) the fusion process in the core will finally run out of atoms to process. As less and less heat is generated in the Core the star beings to cool down, and shrink in size.

The star will first shrink to become a White Dwarf. Then it will cool down to become a Black Dwarf. Press to play Animation Complete

But if the star is large (more than 1.5 times the mass of our sun) the fusion process can continue to make large atoms (up to Iron in the Periodic Table). Once it begins generating Iron, the star will no longer be able to produce enough heat in the core to remain stable.

The star therefore will explode in a Supernova. Leaving behind a super dense Neutron Star. Press to play Animation Complete

However if the star is more than three times the mass of our sun, the Supernova will leave behind a Black Hole. Press to play Animation Complete

Press to play When a Supernova occurs, the outer part of the star (made of Hydrogen) and part of the Core are spread out into space and will cool. This creates a cloud of Hydrogen gas, which (if big enough) can form into a new star – starting the cycle again …. Animation Complete

Important points: Fusion only occurs in a stars core, no Hydrogen is converted to Helium in the outer layer The more massive the star, the faster the process of fusion works (higher temperature and pressure in the core); In generating heat via fusion, the mass of the star stays roughly the same (unlike a fire which gets progressively smaller, and a big star does not become a small star over time);