Faint blue galaxies. True colour Hubble Space Telescope image of irregular faint blue galaxies, the most common class of objects in the early Universe. These are seen here as dim blue spots and patches; other objects are nearer stars and galaxies in the line of sight. The blue galaxies are at a distance of three billion to eight billion light years, and so are seen as they were at an early time in the life of the Universe. Their blue colour is due to intense star-forming activity. The lower population of irregular galaxies today suggests that many were destroyed by mergers or have faded in the intervening years.