The galactic time machine:
light from remote galaxies
Observations of remote galaxies are a window into the past. Light from the remotest of
galaxies in the universe has travelled more than 13 million years before reaching our
telescopes, so we observe the galaxies the way they were when they emitted the light.B.^ S
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Galaxies show the past
1
SPT0615-JD is one of the
most remote galaxies
ever discovered. The
light captured in this image was
emitted 13.3 billion years ago,
when the universe was ‘young’,
around 500 million years old.Remote galaxies are red
2
The further away galaxies
are, the faster they are
moving away from us,
because the universe is expanding.
Light from remote galaxies is hence
‘stretched’ into longer wave-
lengths, i.e. shifted towards red.Close galaxies are blue
3
Light from approaching
galaxies is squeezed
together into lower
wavelengths, so changes colour
towards blue – a blue shift. A similar
phenomenon makes an approaching
ambulance siren sound higher in
frequency than one moving away.SPT0615-JDLight wavesLight wavesClose galaxyRed shiftBlue shiftRemote galaxyscienceillustrated.com.au | 43