Further Physics - Observing the Universe - Inside Stars
The Structure of a Star
A star has three main parts. The Core is the hottest part where fusion takes place. The connective zone is where energy is transported to the surface by convection currents. The photosphere is where energy is radiated into space.
Like all hot objects, stars emit a continuous range of electromagnetic radiation. Hotter objects emit radiation of a...
- higher temperature
- higher peak frequency - ie. frequency where most energy is emitted
than colder objects.
An object that is red hot emits most of its energy in the red frequency range. The frequency of light given off from a star provides evidence of how hot it is.
Using a Star's Spectra
The removal of electrons from a star is called ionisation. The movement of electrons within the atom causes it to emit radiation of specific frequencies called line spectra. Different elements have characteristic line spectra. Due to it's high temperature, the spectrum from a star is a continuous spectrum apart from the spectral lines of the elements it contains (these lines are missing because they are absorbed)
By comparing a star's spectrum to emission spectra from elements we can find which chemical elements the star contains. The sun's spectrum is complex, indicating that it contains more than one element. However, by comparing the spectra we can see that the Sun contains hydrogen as well as some other elements. In the Sun's case we know that this other element is helium.
The Life Cycle of a Star
Stars begin life as clouds of gas (mainly hydrogen). As gravity brings these gas clouds together, they become denser.
The force of gravity pulls the gas inwards, causing the pressure and temperature to increase. As more gas is drawn in, the force of gravity increases. This compresses the gas so it becomes…