<P> The wealth of galaxies at different stages of their evolution also allowed astronomers to estimate the variation in the rate of star formation over the lifetime of the Universe . While estimates of the redshifts of HDF galaxies are somewhat crude, astronomers believe that star formation was occurring at its maximum rate 8--10 billion years ago, and has decreased by a factor of about 10 since then . </P> <P> Another important result from the HDF was the very small number of foreground stars present . For years astronomers had been puzzling over the nature of dark matter, mass which seems to be undetectable but which observations implied made up about 90% of the mass of the Universe . One theory was that dark matter might consist of Massive Astrophysical Compact Halo Objects (MACHOs)--faint but massive objects such as red dwarfs and planets in the outer regions of galaxies . The HDF showed, however, that there were not significant numbers of red dwarfs in the outer parts of our galaxy . </P> <P> Very - high redshift objects (Lyman - break galaxies) cannot be seen in visible light and generally are detected in infrared or submillimetre wavelength surveys of the HDF instead . Observations with the Infrared Space Observatory (ISO) indicated infrared emission from 13 galaxies visible in the optical images, attributed to large quantities of dust associated with intense star formation . Infrared observations have also been made with the Spitzer Space Telescope . Submillimeter observations of the field have been made with SCUBA on the James Clerk Maxwell Telescope, initially detecting 5 sources, although with very low resolution . Observations have also been made with the Subaru telescope in Hawaii . </P> <P> X-ray observations by the Chandra X-ray Observatory revealed six sources in the HDF, which were found to correspond to three elliptical galaxies: one spiral galaxy, one active galactic nucleus and one extremely red object, thought to be a distant galaxy containing a large amount of dust absorbing its blue light emissions . </P>

The hubble telescope deep field view big bang