The Most Distant Objects Observed

The most distant things that astronomers can see are about 18,000,000,000 light years away. Thus, the light that we presently see from these objects began its journey to us about 18 billion years ago. Since that is close to the estimated age of the Universe, this light is a kind of "fossil record" of the Universe not long after its birth! Thus the observation of very distant objects is in a very real sense equivalent to looking backwards in time.

Until recently, the most distant objects were quasars. Now however, examination of the Hubble Deep Field has revealed galaxies that may be further away than the most distant quasars (Ref). The image adjacent left shows what may be the most distant object yet observed. It is the faint red smudge at the tip of the arrow, and appears to be a galaxy further away than any quasar (Ref). If the indirect method of estimating their distance is reliable, at least six galaxies (including the one in the adjacent image) may be so far away that we are seeing them when the Universe was less than 1 billion years old. If so, this implies that the formation of galaxies started relatively soon after the big bang.

A Technique for Identifying Distant Galaxies
The distant galaxy identification technique used here relies on the Hubble Law that more distant galaxies will be more redshifted. By looking at distant galaxies using different filters to emphasize light of different wavelengths, and then comparing the results for unknown galaxies with a control group of galaxies for which the distance is already known, it is argued that statistically one can determine distances to the most distant galaxies. By statistical, we mean that there could be error in the determination for any one galaxy, but for a set of galaxies the results will be reliable, on average. The technique is illustrated in the following figure.

Here four filters have been used on the Hubble Space Telescope to emphasize progressively shorter wavelength light from right to left in the four images. The galaxy indicated by the arrow is only seen easily in the near IR region of the spectrum, indicating that it has a very large redshift and therefore is distant.