Edexcel IGCSE Physics: Double Science 复习笔记:8.2.3 The Life Cycle of Larger Stars

Edexcel IGCSE Physics: Double Science 复习笔记:8.2.3 The Life Cycle of Larger Stars

The Life Cycle of Larger Stars

 

  • large star is one that is much larger than the Sun
    • Stars that are larger than the Sun have much shorter lifespans – in the region of hundreds of millions of years (instead of billions)

     

  • The life cycle of a star larger than the Sun starts in the same way as a solar mass star

 

1. Nebula

  • All stars form from a giant cloud of hydrogen gas and dust called a nebula

 

2. Protostar

  • The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar
  • As the particles are pulled closer together the density of the protostar will increase
    • This will result in more frequent collisions between the particles which causes the temperature to increase

     

 

3. Main Sequence Star

  • Once the protostar becomes hot enough, nuclear fusion reactions occur within its core
    • The hydrogen nuclei will fuse to form helium nuclei
    • Every fusion reaction releases heat (and light) energy which keeps the core hot

     

  • Thermal expansion from fusion reactions occur within its core and the force of gravity keeps the star in equilibrium
  • At this point, the star is born, and it becomes a main-sequence star
  • During the main sequence, the star is in equilibrium and said to be stable
    • The inward force due to gravity is equal to the outward pressure force which results from the expanding hot gases inside the star

     

 

4. Red Supergiant

  • Eventually, the main sequence star will reach a stage when it starts to run out of hydrogen gas in its core
  • Once this happens, the fusion reactions in the core will start to die down
  • This causes the core to shrink and heat up
    • The core will shrink because the inward force due to gravity is greater than the outward force due to the pressure of the expanding gases

     

  • A new series of fusion reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium
  • These fusion reactions will cause the outer part of the star to expand and it will become a super red giant
    • A super red giant is much larger than a red giant

     

 

5. Supernova

  • Once the fusion reactions inside the red supergiant finally finish, the core of the star will collapse suddenly causing a gigantic explosion
    • This is called a supernova

     

  • At the centre of this explosion a dense body, called a neutron star will form
  • The outer remnants of the star will be ejected into space during a supernova

 

6. Neutron Star (or Black Hole)

  • At the centre of this explosion a dense body, called a neutron star will form
  • In the case of the largest stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
    • A black hole is an extremely dense point in space that not even light can escape from

     

 

 

7.1.7-Lifecycle-of-Larger-Mass-Stars

 

Lifecycle of stars much larger than our Sun

 

 

Exam Tip

Make sure you remember the life cycle for a high mass star and ensure you can describe the sequence in a logically structured manner in case a 6 marker comes up in the exam!Ensure you can remember the end stages for a high mass star clearly (red supergiant, supernova, neutron star/black hole) as this is different for a star that is a similar size to the Sun!

转载自savemyexams

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