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Objects in the universe



Data II







stable equilibrium

Birth of star


Stellar Nurseries

Nebula are the birthplace of stars and are often referred to as stellar Nurseries. Nebulae are gigantic clouds of dust and particles (mainly hydrodgen ). Every star has its own journey from birth to death. Our very own sun was born in a nebula.

stellar nurseries

  • Nebula are formed by the tiny graviational attraction between the dust and the particle ( forming vast clouds)a
  • These vast clouds of gas and dust collapse due to gravity. As the dust and particles get closer together the graviational attraction accelerates.
  • A dense core (protostar), forms at the center as more material accumulates. The dense core pulls in more dust and particles under the force of gravity, ganing mass, and getting more denser.
  • The accumalting mass in protostar core, leads to an increase in temperature and pressure. ( Gravitational potential energy transfers to thermla energy.
  • A protostar is not a star but a very hot and dense sphere of cloud and dust.

Formation of a protostar

The accumilation of mass in the protostar, continues until the conditions at the core reach a critical point, allowing for nuclear fusion reactions to commence, marking the birth of a main sequence star. Nuclear fusion needs to start in the core. Fusion reactions produce energy in the form of kinetic energy Extremely high pressures and temperatures in the core are needed to overcome the electrostatic repulsion between the hydrogen nuclei. So that the hydrogen nuclei can fuse together to form helium nuclei.Many protostars never reach this stage.As more and more mass is added to the protostar, it grows so large and so hot that kinetic energy is large enough to overcome the electrostatic reoulsion. Where the hydrogen nuclei are fused together to from helium nueclei.A star is born

A Star is formed

Star Life

  • Once a star is formed it remains in stable equilibrium
  • The gravitional forces act to compress
  • The radiation pressure (from photons emitted during fusion) and gas pressure from the nuclei in the core push ooutwards
  • the forces from the radiation and gas pressure balance the forces of gravitational attraction and maintains equilibrium.
  • Stars at this stage are known as main sequence stars.

Star life

  • How long a star remains depends on the mass of its core.
  • The core of large supergiants, are much hotter than those of small stars
  • Large supergiants release more power and convert the available hydrogen into helium in a much shorter time. Really large stars, are only stable for a few million years.
  • Whereas smaller stars like our sun are stable for 10 of millions of years. This is because the core of smaller stars are less dense, so convert hydrogen into helium in longer amount of time. So smaller stars are stable for longer.

formation of a star

A star is formed

nuclear fusion takes place and a star is born


A dense core is formed (protostar), due to graviational atrraction

Dark cloud (Nebula)

Nebula are clouds of dust and gas (mainly hydrogen)

Star formation


A star is born

Nucleur fusion occurs in the protostars core.Extremely high pressure and temperature inside core are needed to overcome the electrostatic repulsion between hydrogen nuclei in order to fuse them with helium nuclei. Radiation and gas pressure are released in nuclear fusion.Once a star is formed, it remains in equilibrium.Pressure acting outwards ( radiation and gas from fusion), balances out the force from the gravitaional attraction. So maintains equilibrium.

  • In one part of the cloud, a protostar froms
  • A protostar is not a star, but it is a very dense and hot sphere of dust and gas.
  • This is due to the gravitational collapse of an insersteller cloud of dust and gas
  • These dense regions pull in more matter, gaining mass and getting hotter.


  • The Digram shows a nebula, contaning clumps of dust and gas, that have pulled towards eachother by graviational attraction.
  • This eventually froms vast clouds