CANDELS UDF

This may not look like the Hubble Space Telescope’s most dramatic image, but what you are seeing here is the history of the universe. This ultra deep field (UDF) is not a star field but a field of galaxies, stretching across half the observable universe in both space and time. The oldest and most distant galaxies depicted appear red, because as the universe expands their light has been stretched or “redshifted” to longer wavelengths. Red is the longest wavelength our eyes can see; beyond it are longer infrared wavelengths, which some telescopes, including Hubble, can detect for us.

The brightest spots that appear to have x-shaped beams of light emanating from them are foreground stars between Hubble and the distant galaxies. The x-shaped light is characteristic of Hubble diffraction spikes, which are optical artifacts caused by the mirror support structure in most reflector telescopes.

The image is the result of the CANDELS project—the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, Hubble’s most lengthy and detailed science observation. Gathering all the detailed data to create this image took Hubble 1450 hours, or the equivalent of 60 continuous days of observation.