Describe the processes involved in stellar formation

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Describe the processes involved in stellar formation

  • Stellar formation begins with the gravitational contraction of a vast nebula of dust and molecular gas.
  • If the nebula mass exceeds the Jeans mass, the gravitational force within it is greater than any thermal pressure outwards, causing the cloud to begin to collapse and form a growing core of matter at its centre.
  • The increasing gravitational attraction of the core causes the contraction to accelerate.
  • The density increases more quickly at the centre, and being denser, it experiences greater gravity and its contraction accelerates further.
  • This causes the cloud to have two parts:
    • A rapidly contracting core.
    • Slower contracting surroundings.
  • As the core contracts, the gravitational potential energy of its gas particles coverts to kinetic energy, causing heat.
  • The heat creates an outward pressure that works against the gravitational collapse, only slightly at first.
  • As the core becomes hotter, the pressure builds, slowing and eventually stopping the collapse and stabilising the size of the core.
  • At this stage, the core becomes known as a protostar.
  • The surrounding material continues to contact, increasing the mass of the protostar.
  • The protostar slowly shrinks, heating its core further.
  • Eventually, the core ay reach a temperature high enough to trigger the nuclear fusion of hydrogen within it.
  • This new long-lasting energy source stabilises the star.
  • The new star is known as a zero-age main sequence star and has a mass between 0.01 and 100 solar masses:
    • Were it smaller, it would not have heated sufficiently to begin fusion.
    • Were it larger, it would have overheated and blown itself apart.