The Galaxies

We assume the stars to be gathered together into galaxies and that these form the basic building blocks of the visible matter in the Universe. Many of the galaxies are similar to our own Milky Way, but many are rather different.

The adjacent image shows the Hubble Deep Field: the Hubble Space Telescope was pointed at the same region of the sky (in the constellation Ursa Major) for 10 consecutive days and images were combined to give the most distant optical view of the Universe yet obtained. In this image, almost every smudge is a galaxy, and objects down to visual magnitude +30 can be seen (Ref).

Because looking out to such large distances implies looking back in time because of the finite speed of light, this image is actually giving us a view of the Universe early in the history of galaxy formation. This image may represent what the Universe looked like only a billion years or so after the Big Bang.

References:

• Other Galaxies and Active Galaxies
• Galaxies