Astronomers found four red galaxies 13 billion light-years from Earth, a discovery that suggests a missing link between the earliest galaxies and the Milky Way.

Researchers remained stumped as to what made the clustered galaxies so red.

The star-gazers identified the distant worlds with NASA's Spitzer Space Telescope launched in 2003 that specifically detects infrared light, instead of visible light detected by the Hubble telescope.

Hubble has shown us some of the first protogalaxies that formed, but nothing that looks like this, Giovanni Fazio study co-author and astronomer with Harvard-Smithsonian Center for Astrophysics, said in a statement. In a sense, these galaxies might be a 'missing link' in galactic evolution.

Astrophysical Journal published the story online Thursday.

The researchers hypothesized that the galaxies may be red from a combination of dust, older stars or extreme distance, factors associated with red-tinted galaxies.

There's evidence for others in other regions of the sky. We'll analyze more Spitzer and Hubble observations to track them down, Fazio said in a statement.