Hot on the heels of that fabulous Spitzer image comes news that Hubble and Spitzer have teamed up to find what may be the most distant galaxy ever seen. It appears to be at a distance of 12.8 billion light years. Yikes. Here's the image (click to make it more cromulent):
The big image shows the incredible galaxy cluster Abell 1689, a well-studied city of galaxies. The combined gravity of the galaxies in that cluster act as a lens, distorting and magnifying the light of galaxies on the other side, more distant galaxies that might be too faint to be seen on their own. The arcs you see are all more distant galaxies, their light strewn out by the gravity if the intervening cluster (see how they all appear to have the center of the cluster as their own center of curvature?). Even boosted by this gravitational lens, the light of the distant galaxy named A1689-zD1 is too faint to be detected in the visible, but Hubble's infrared camera NICMOS got a peek at it. Then the Spitzer Space Telescope was able to see it even more clearly, as can be seen by the three images on the right. The more distant galaxies we see, the younger they are, because it takes light a long time to cross the Universe. We see this galaxy as it was when the Universe itself was only about a billion years old. Astronomers are not sure how long it took galaxies to form after the Big Bang, but every time we look farther away, we still see galaxies. Mind you, the ones we see have to be fantastically bright, so they may be skewing our view (there may be much dimmer ones, but they are as yet too faint to see). But the point is, we do see galaxies at this fantastic distance. The distance was determined by looking at the colors of the galaxy. The Universe is expanding, and more distant galaxies recede from us more quickly. This stretches the light from distant objects out, making them redder, a cosmic variation on the more familiar Doppler shift that makes car engines make that WWEWEEEEEOOOOOORRRR sound as they pass. By knowing what kind of light a young galaxy emits, and then comparing it to the amount of light in each image, the amount of redshift can be estimated, and the distance determined. For A1689-zD1, it's invisible in visible light, detectable at near infrared wavelengths, and stronger yet in the longer infrared colors. This indicates a tremendous redshift, and therefore a great distance. From my rough calculation, it may be possible to nail down the redshift using STIS, a camera on board Hubble. STIS is currently dead, the victim of an electrical short. However, astronauts will attempt a repair of it in September during the Hubble servicing mission. I wonder if it's worth trying to observe the galaxy... it's a marginal observation; it's possible that even if STIS can detect this faint smudge, it will only be able to give us a lower limit to the distance (in other words, the data will say that the galaxy is at least at a distance of X billion light years, but not tell us what the actual distance is). Still, it might be worth a shot. By knowing the distance to this galaxy, and examining the way it emits light, we can put yet another data point in our models of the early Universe. We're still trying to figure out just what the heck the cosmos was doing back then, and every time we see farther back, we nail down a little bit more about this place we live in. Observations like this one from Hubble and Spitzer propel us that much farther in our understanding.
