Notes

P7.4
Stars emit a continuous range of e.m radiation whose luminosity and peak frequency increase with temperature.
Ionisation - removal of electrons from atoms.
explain how electron
energy levels within atoms give rise to line spectra
Specific spectral lines in the spectrum of a star provide evidence of the chemicals present in it.

-273 = absolute zero

The pressure of a gas is inversely proportional to the volume.
Pressure x Volume = Constant
Pressure / Temperature = Constant
Volume / Temperature = Constant

Protostar Formation
1) Gravity pulls together a cloud of gas which contains hydrogen and helium.
2) The cloud of gas collapses and its temperature increases due to the reduced volume and increased pressure.
3) This causes hydrogen and helium nuclei to fuse releasing energy. These reactions release positrons and neutrinos to conserve the charge.
4) Energy is liberated when light nuclei fuse and goes up to the mass of an iron nucleus.
5) The more massive the star, the hotter the core and the heavier the elements that can be produced. The core of the star is where the most nuclei are made.

Energy is transported from the core to the surface by photons and convection.
It is then radiated from the photosphere.

A star leaves the main sequence when the hydrogen runs out.
It then becomes a red giant or supergiant and the photosphere cools. Helium nuclei fuse to make carbon followed to produce nuclei such as nitrogen and oxygen.

Low-mass stars become red giants because there isn't enough mass to compress the core further so shrinks to become a white dwarf.
In a white dwarf there is no nuclear fusion so the star gradually fades.
High-mass stars can produce nuclei up to iron, and when the core is mostly iron it explodes as a supernova creating nuclei with masses greater than iron and leaves a dense neutron star or a black hole.