Star-forming galaxies, c 2000.
© National Aeronautics & Space Administration / Science & Society
These faint sources, circled in the image, can help astronomers discover when the first galaxies formed and what their properties might be. The sensitivity of Hubble's Advanced Camera for Surveys (ACS), combined with the penetrating power of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), finally revealed these long-sought faint galaxies. The Hubble Ultra Deep Field (HUDF) shows that close to a billion years after the Big Bang the early universe was filled with dwarf galaxies, but no fully formed galaxies like our Milky Way. After careful analysis, they have been sorted out as between 54 and 108 dim, red smudges sprinkled across the HUDF image.