The life history of a star Objectives To
The life history of a star Objectives: To describe the sequence of events from the birth to the death of a star.
How is a star formed? Write a sentence to describe how a star is formed. (use the following key words: fusion, protostar, nebula, gravity, hydrogen, helium)
Life Cycle of a Star - Birth New stars being created in the Orion nebula.
Life Cycle of a Star - Birth Star-Birth Clouds in M 16: Stellar "Eggs"
Protostar pressure Task: Explain why a protostar contracts and describe what happens to the protostar as it contracts.
Finding stability When the temperature in the core of a protostar reaches roughly 14 million Kelvin, nuclear fusion begins and a stable star is born. The star now enters its stable phase. A star is stable when its size remains constant over time. All stars have a stable period in their lives, the length of which is determined by their mass. The Sun is halfway though its nine billion year stable phase.
What makes a star stable? Inside a star, the energy released by However, the star’s huge mass means that gravity is acting in the fusion produces an outward opposite direction, forcing particles acting force. towards the core. This causes star expansion. explosive force of fusion (radiation pressure) gravitational force 332, 948 Earth masses If these two forces are equal, then the star will not change its size. It is said to be stable as is then known as a main sequence star. Task: Draw a simple FORCE DIAGRAM of the Sun to illustrate how the Sun is able to exist in a stable state.
The death of a star Task: Put the following terms in the correct sequence to describe the death of our Sun (average star): WHITE DWARF MAIN SEQUENCE STAR BLACK DWARF RED GIANT
The end of stability A star’s stable phase ends when most of its hydrogen has been consumed by fusion. The reduction in fusion causes the core to cool. This lowers the pressure causing the star to collapse upon itself under its own gravity. As the outer layers contract, they heat up. This triggers the fusion of the remaining hydrogen. The increased energy output in the outer layers causes them to expand. Star increases massively in size, becoming a red giant. Task: Explain what causes a star to ‘bloat’ into a red (super) giant.
What happens in the core? The core continues to contract. This causes it to reach new extremes of temperature (over 100 million Kelvin) and pressure. This gives helium atoms enough energy to fuse. Thus heavier atoms, such as carbon and oxygen, are produced. In the largest stars elements as heavy as iron can be produced. However such large stars will suffer a different fate to the Sun.
Red supergiants Draw a FLOW DIAGRAM to describe the death LARGE and VERY LARGE stars: RED SUPERGIANT BLACK HOLE SUPERNOVA NEUTRON STAR
Death of a Star - Black Hole This image is believed to show high energy electrons being emitted from a black hole in the centre of Galaxy M 87.
Life Cycle of a Star - Summary M = Mass of the Sun Average Star Red Giant Planetary Nebula White Dwarf <8 M Neutron Star >8 but <20 M Stellar Nebula >20 M Massive Star >8 M Red Supergiant Supernova Black Hole
Over a spun (1) supernova Tired (2) Red nag giant Return Neutron a snot star(2) White Fed withdwarf war (2) Black hole(2) Hello back Dr. Black back dwarf flaw (2) nebula(1) Unable
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