ESA Science & Technology - Hubble and Spitzer Uncover Smallest Galaxy Building Blocks

The bottom row of pictures shows five of the nine compact galaxies in the HUDF studied by Pirzkal et al. [2007], with their distance expressed in redshift in the lower right corner. Three of the galaxies appear to be slightly disrupted. Rather than being round-shaped, they appear stretched into tadpole-like forms. This is a sign that they may be interacting and merging with neighbouring galaxies to form larger structures.

The detection required joint observations between Hubble and NASA's Spitzer Space Telescope. Blue light seen by Hubble shows the presence of young stars. The absence of infrared light from Spitzer observations conclusively shows that these are truly young galaxies without an earlier generation of stars.