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Astronomers recently spotted seven galaxies that appeared around 13.1 billion years ago - 700 million years after the Big Bang.

Where the galaxies came from initially confused the experts because they seemed to appear almost out of nowhere, very rapidly.

But now the team behind the observations suggest the previously hidden cluster of stars appeared when a cosmic 'fog' cleared. 

These colour composite images from the Subaru Telescope show the seven galaxies found in the study, as they would have looked 13.1 billion years ago - but their sudden appearance is a bit of a mystery. They have a red colour due to the effects of cosmic expansion on their light

The latest discovery, published in the Astrophysical Journal, was made by a team of astronomers at the University of Tokyo using the Subaru Telescope in Japan.

Although earlier galaxies have been spotted by the Hubble Space Telescope, the telescope is significant as it looks for a particular type called Lyman-alpha Emitters (LAEs).

LAEs were primitive, low mass galaxies and are among the oldest types known in the universe.

They are thought to have been the progenitor for modern, Milky Way-type galaxies.

Using the telescope, the team, led by graduate student Akira Konno and Dr Masami Ouchi, were looking to find the role LAEs played in an event called 'cosmic reionisation'.

When the universe was 400,000 years old, conditions were cool enough to allow the protons and electrons to bond and form neutral hydrogen atoms.

That event is called 'recombination' and resulted in a universe filled with a 'fog' of these neutral atoms.

Eventually the first stars and galaxies began to form, and their ultraviolet light ionised - or energised - the hydrogen atoms, and 'divided' the neutral hydrogen into protons and electrons again.

As this occurred, the 'fog' of neutrals cleared.

Astronomers call this event 'cosmic reionisation' and think that it ended about 12.8 billion years ago - about a billion years after the Big Bang.

The timing of this event - when it started and how long it lasted - is one of the big questions in astronomy.

To investigate this cosmic reionisation, the Subaru team searched for early LAE galaxies at a distance of 13.1 billion light years. 

'At first we were very disappointed at this small number,' Mr Konno said.

'But we realised that this indicates LAEs appeared suddenly about 13 billion years ago.

'This is an exciting discovery. We can see that the luminosities suddenly brightened during the 700 to 800 million years after the Big Bang. What would cause this?' 

The latest discovery, published in the Astrophysical Journal, was made by a team of astronomers at the University of Tokyo using the Subaru Telescope (pictured) in Japan. Although earlier galaxies have been spotted by the Hubble Space Telescope, Subaru is significant as it looks for Lyman-alpha Emitters (LAEs)

In the team's analysis, they suggest neutral fog that once filled the universe began to clear about 13 billion years ago, which resulted in LAEs suddenly appearing for the first time. Shown left is a distant LAE and right is what one might look like from up close

According to the team's observations, one reason that LAEs appeared very quickly is cosmic reionisation.

LAEs during the time of cosmic reionisation became darker than their actual luminosity due to the presence of the neutral hydrogen fog.

In the team's analysis, they suggest the possibility that the neutral fog filling the universe was cleared about 13 billion years ago and LAEs suddenly appeared in sight for the first time.

'However, there are other possibilities to explain why LAEs appeared suddenly,' said Dr Ouchi, the principal investigator on the programme.

'One is that clumps of neutral hydrogen around LAEs disappeared. Another is that LAEs became intrinsically bright.

'The reason of the intrinsic brightening is that the Lyman-alpha emission is not efficiently produced by the ionised clouds in a LAE due to the significant escape of ionising photons from the galaxy.

'In either case, our discovery is an important key to understanding cosmic reionisation and the properties of the LAEs in early universe.'