These are four views of the 18th-magnitude quasar QSO 1208+101, obtained with the HST through filters of various colors. They are shown here in false color, added by means of computer processing. With a red shift of 3.8, QSO 1208+101 was the most distant known object in 1986 when it was discovered as a ground-based telescope. Although large distances in the universe are not accurately calibrated, it must be roughly 10 billion light years from Earth. Several quasars at even greater distances have since been discovered.
As the HST pictures clearly show, there is a second, somewhat fainter light source within one-half of an arc second of QSO 1208+ 101. The brightness of the second source relative to the quasar is the same when seen through each of the four filters. This strongly suggests that the two sources seen in these images are gravitationally lensed images of the same very distant quasar. If the fainter object were a foreground star, its color would almost certainly be different from the quasar's, and so it would not have the same relative brightness through all four filters. If it were a red star, for example, the fainter object would appear relatively brighter in the image taken through a red filter.
Whatever is acting as the gravitational lens is too dim to be seen in this image and its nature remains unknown.
Camera: WF/PC-1
Credit: J. Bahcall (Institute for Advanced
Study, Princeton), and NASA
