The Life Cycle of Stars Stars form from
- Slides: 16
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. Gravity Animation Complete Press to play
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. H H He Animation Complete Press to play
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. H H He Animation Complete Press to play
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. H H He Animation Complete Press to play
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. Animation Complete Press to play
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. Animation Complete Press to play
However if the star is more than three times the mass of our sun, the Supernova will leave behind a Black Hole. 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 Press to play
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);
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