Space

• Becoming a protostar:

  • a dust and gas cloud is present in a galaxy (a nebula) – pulled together due to gravitational attraction

  • the cloud becomes more concentrated as the particles get close – a protostar
• Becoming a main sequence star :

  • the temperature and pressure of the particles increases

  • eventually the pressure is so great that the gas/dust particles are able to fuse

  o fusion occurs as hydrogen nuclei fuse to form helium nuclei which releases huge amounts of energy

  • eventually an equilibrium forms between the energy released from fusion which causes an outward pressure and the pressure of gravitational attraction

  o the star now enters a long stable period of several billion years (a main sequence star)
• Becoming a supernova:

  • eventually the star runs out of hydrogen to fuse, this breaks the equilibrium

  • if the star is massive (larger than our sun)

  o star swells into a red super giant – fusion of helium begins, elements up to iron are formed in the core

  o then as the amount of fusion occurring increases the star begins to glow brightly again and expand, forming elements as heavy as iron – the star then explodes in a supernova

  o forming elements heavier than iron and ejecting them into the universe to form planets and stars
• Becoming a black hole:

  o the exploding supernova throws the outer layers of dust into space leaving a very dense core – a neutron star

  o if the star is massive enough, it will become a black hole (a super dense point where light can’t escape)
• • if the star is normal sized (around the size of our sun)

  o star swells into a red giant – fusion of helium begins, elements up to iron are formed in the core

  o star becomes unstable and ejects its outer layer of dust leaving a hot, dense solid core (a low scale supernova) - a white dwarf

  o as a white dwarf cools, it emits less and less energy until it no longer emits a significant amount – a black dwarf
• • the supernova of a massive star produces and distributes elements throughout the universe
• • gravity provides the force that allows planets and satellites (natural and artificial) to maintain circular orbits

  o the gravitational force causes the planet to constantly change direction

  o so its velocity is always changing (speed remains unchanged) which means it is constantly accelerating
• • for a stable orbit, if the planet moves closer to the sun (the orbital radius decreases)

  o the gravitational attraction to the sun increases (along with the acceleration)

  o so the orbital seed of the planet increases

  • so faster moving objects have a smaller orbital radius than slower moving ones
• • there is an observed increase in the wavelength of light from the most distant galaxies

  o the further away the galaxy, the faster they are moving and the greater the increase in wavelength observed – this is called red-shift (as the wavelengths move closer towards the red end of the spectrum)
• • red shift provides evidence that the universe is expanding because...

  o more distant galaxies have greater red-shifts than nearer ones

  o meaning the more distant galaxies are moving away faster than nearer ones
• red shift also provides evidence for the Big Bang theory

  o this suggests that the universe began from a small region that was extremely hot and dense which exploded which started expansion still occurring today

  o along with Cosmic Background Radiation (just after the Big Bang everything would’ve been extremely hot and emitted short-wavelength radiation, as the universe expands this stretches to become microwaves – this radiation if present everywhere in the universe proving that the universe has cooled and expanded)
• o dark matter holds galaxies together but doesn’t emit any electromagnetic radiation

  o dark energy is though to be responsible for the acceleration of the expansion of the universe
• Life cycle of star order for stars the same size as the Sun?

  Nebula

  Protostar

  Main Sequence star

  Red Giant

  White Dwarf

  Black Dwarf
• Life cycle of star order for stars much bigger than sun?

  Nebula

  Protostar

  Main Sequence Star

  Red Super Giant

  Supernova

  Neutron Star

  Black Hole