Space Physics

Space Physics

1. Formation of the solar system

   • 1. gravitational forces pull clouds of dust and gas together to form a protostar
   • 2. The protostar becomes denser and the nuclei of hydrogen atoms and other light elements start to fuse together. Energy is released in the process so the core gets hotter and brighter
   • 3. Stars radiate energy because of hydrogen fusion in the core. This stage can continue for billions of years until the star runs out of hydrogen nuclei in its core
   • 4. The star is stable because the inward force of gravity is balanced by the outward force of radiation form the core this is called a main sequence star
   • 5. Objects that are too small to become stars can be attracted by protostars to become planets orbiting the stars.
     • our solar system consist of the sun, its orbiting planets and other smaller objects such as moons and comets

2. Life cycle of a star

   • 1. once a main sequence star has run out of helium, it will swell, cool down and turn red. A star of a similar size to the sun will become a red giant.
   • 2. at this stage helium and the other light elements in the core fuse to become heavier elements. Fusion stops and the star will contract to form a white dwarf. Eventually no more light is emitted and the star becomes a black dwarf
   • 3. a star much larger than the sun will swell to become a red supergiant which then collapses. Eventually the star explodes in a supernova
     • 4. elements heavier than iron are only formed in the final stages of the life of a big star. This is because the process requires the input of so much energy. All the elements get distributed through space by the supernova explosion
   • 5. during the supernova the outer layers are thrown into space and the core is left as a neutron star. If this is massive enough it becomes a black hole. The gravitational field of a black hole is so strong not even light can escape from it.

3. Planets, Satellites and orbits

   • The earth moves around the sun in a path called and orbit. The other planets orbit the sun, and the moon and satellites orbit the earth. Orbits are in circular or almost circular motions, smaller objects orbit larger objects
   • A force is needed to keep the smaller object moving along its orbit. The force is the force of gravity between the bigger object and the smaller object
   • As an object moves around an orbit, its velocity is continually changing, it accelerates towards the centre of the orbit. The direction of the velocity is always at right angles to the direction of the gravitational force on it, the gravitational force is always towards the centre of the bigger object.
   • The force needed to keep and object moving in a circle is called the centripetal force, which always acts towards the centre of the circle. For something orbiting around a bigger object this force is gravity. This force is alas the resultant force, the acceleration is towards the centre of the orbit
     • for an object to orbit at a particular distance it must go at a particular speed. If the distance decreases, the speed will increase. Too great a speed and the object will fly off into space, too small a speed and the object will fall down to earth

4. The expanding universe