How old are the oldest galaxies? Faint red smudges (circled) on the deepest optical sky image (click to embiggen) ever taken may well be members of the first class of galaxies. Detailed inspection of the Hubble Ultra Deep Field taken by the Hubble Space Telescope found the galaxies and used their distance and abundance to probe the universe when it was but a small fraction of its present age. Analyses indicate that all members of this class of galaxies are dwarf galaxies from which larger modern galaxies must have formed. Some large modern galaxies shine brightly in the colorful foreground. The early dwarf galaxies probably contained energetic stars emitting light that transformed much of the remaining normal matter in the universe from a cold gas to a hot ionized plasma.
Image Credit: NASA/ESA/ASU/CalTech