Evolution of Spiral Galaxies
This image shows the evolution of spiral galaxies, from fully formed structures to disheveled collections of stars just beginning to form. These galaxies were captured in the Great Observatories Origins Deep Survey (GOODS) and are presented in the IMAX short film "Hubble: Galaxies Across Space and Time." It takes billions of years for the light of a distant galaxy to reach Earth. Consequently, we see such galaxies as they were in the past, and can thus assemble a rough pictorial history of galaxy evolution.
The galaxies at lower left are located up to 3 billion light-years from Earth, which means the galaxies are seen as they existed up to 3 billion years ago. These galaxies show the fully developed structures of mature galaxies.
The galaxies at center are located 3 to 7 billion light-years away, and are seen as they were 3 to 7 billion years ago. The spiral structure in these galaxies is somewhat less developed. The galaxies appear more yellow because their colors have been shifted toward redder wavelengths by cosmological redshift - the stretching of light as it crosses expanding space. The galaxies' smaller apparent size is simply due to their greater distance.
Finally, the galaxies at upper right are located 7 to 10 billion light-years away, and are seen as they existed 7 to 10 billion years ago. These galaxies show disk structures, but generally weakly defined spiral arms. Their colors have been shifted all the way to redder wavelengths. The blue regions are pockets of intense star formation. The stars' ultraviolet light has been shifted into the blue wavelengths. The smaller apparent sizes are mainly due to greater distance, but also reflect their incomplete formation.
These galaxies are a few of the nearly 30,000 galaxies captured by the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope.