Although astronomers have uncovered many of the details revealing the life cycles of individual stars, they still do not completely understand how galaxies, like our Milky Way, begin and end their lives. The problem is that, although stars within the Milky Way may be seen in a variety of evolutionary stages, few examples of young galaxies are known, and their images come to us from the most distant edge of our visible universe. That is, because of the finite speed of light, observing galaxies at large distances is equivalent to looking back in time to the early history of the Universe, as the image shown above indicates (click the image for an explanation).
|Galaxies: Snapshots in Time (Explanation)|
|Distant cluster of galaxies (Explanation)|
The following image shows galaxies from an even earlier time.
|Galaxies in the Young Universe (Explanation)|
These galaxies are about 12,000,000,000 light years away; thus, they represent the Universe when it was only a few billion years old. Click on the image for an explanation of this figure. A discussion of the newest evidence for the Universe's early evolution may be found in this this NASA press release.
The figure shown below
is a Hubble Space Telescope image of a cluster of
galaxies approximately 8 billion light years away (one of the most distant galaxy clusters known)
in which there is evidence for a very large amount
of current and recent interaction between galaxies. Among the hundreds of galaxies in the image, 13 have
been identified as presently
undergoing or recently participating in collisions (see the blowups in the right panels
of the image).