Astronomers using ESO’s Very Large Telescope (VLT) have measured the distance to the most remote galaxy so far, UDFy-38135539, existing when the universe was only about 600 million years old (a redshift of 8.6). At this early time, the universe was not fully transparent and much of it was filled with a hydrogen fog that absorbed the fierce ultraviolet light from young galaxies. The transitional period when the fog was still being cleared by this ultraviolet light is known as the era of reionization, illustrated with this still from a representative scientific simulation.
ESO/M. Alvarez, R. Kaehler, T. Abel