Galactic Redshift (AQA A Level Physics)

Galactic Redshift

• When spectral lines from a distant galaxy are redshifted, this means:

  The lines have shifted towards a longer wavelength, or towards the red end of the spectrum

• This shift can be observed by comparing the spectra from the distant galaxy to a spectrum produced by a nearby object, such as our Sun, or a laboratory sample

Comparing the light spectrum produced by the Sun with light from a distant galaxy

An Expanding Universe

• After the discovery of redshift, astronomers began to realise that almost all the galaxies in the Universe are receding

  • This led to the idea that the space between the Earth and the galaxies must be expanding

• This expansion stretches out the light waves as they travel through space, shifting them towards the red end of the spectrum

• The expansion of the Universe can be compared to dots on an inflating balloon

  • As the balloon is inflated, the dots all move away from each other

  • In the same way, as the rubber stretches when the balloon is inflated, space itself is stretching out between galaxies

  • Just like the dots, the galaxies move away from each other, however, they themselves do not move

• Another observation from looking at the light spectra produced by distant galaxies is that the greater the distance to the galaxy, the greater the redshift

  • This means that the greater the degree of redshift, the faster the galaxy is moving away from Earth

The further a galaxy is from Earth, the greater its redshift tends to be

The furthest galaxies appear to be redshifted the most and are receding the fastest