PhysicsCode 5054
Stars
What this topic asks you to be able to do
- state that: (a) every galaxy consists of a huge number of stars, numbering in the billions (b) our star, the Sun, belongs to the Milky Way galaxy (c) the rest of the stars in the Milky Way lie at far greater distances from Earth than the Sun does (d) cosmic distances may be expressed in light-years, with a light-year being how far light moves through a vacuum in a single year
- Describe a star's life cycle: (a) stars form out of interstellar clouds of dust and gas containing hydrogen (b) a protostar is one of these clouds collapsing and heating up, pulled inward by its own gravitational attraction (c) once the outward force caused by the high temperature at its centre balances the inward force of gravity, the protostar has become a stable star (d) sooner or later every star runs short of the hydrogen that fuels its nuclear reaction (e) when most of the hydrogen at the centre has turned into helium, most stars swell into red giants, while stars of greater mass swell into red supergiants (f) a red giant that came from a lower-mass star becomes a planetary nebula, leaving a white dwarf in the middle (g) a red supergiant blows apart in a supernova explosion, producing a nebula of hydrogen together with newly formed heavier elements and leaving either a black hole or a neutron star in the middle (h) new stars, with planets orbiting them, may later form from the nebula a supernova leaves