Friday, July 13, 2007

A long, long, long time ago in a galaxy far, far, even further away...

Earlier this week, astronomers using the Keck Observatory announced that they have seen the most distant galaxies yet known. And, since looking further away is looking backward in time, these galaxies are also our first glimpse of the first galaxies forming.

These galaxies are so far away that their exact distances are hard to determine and depend on our understanding of the evolution of the Universe. We think these galaxies are about 13.2 billion light-years away; the light we see has been travelling since the Universe was "only" 500 million years old. How can we even see so far away?

These galaxies are all located behind massive clusters of galaxies. The combined gravity of thousands of galaxies and loads of dark matter acts as like a giant telescope, focusing light from these galaxies and magnifying the images. With the largest telescopes on Earth, we can just barely see the light from these galaxies. In fact, it is so hard to see them that we can't be sure that these galaxies are not actually much closer and very faint. For various reasons the discoverers of these galaxies are pretty sure that they are very distant, but they could be many times closer.

The importance of this study is not the detection of the most distant galaxies in the Universe. More important is that these galaxies tell us that the Universe was making stars in a very short amount of time after the Big Bang. It is difficult for theories of the Universe to produce stars this early, so detection of galaxies at such a time helps push the theories to work harder to reproduce what we see.

This doesn't mean that we don't have a good understanding about the Big Bang, though. We understand that quite well. What we don't understand well is how clouds of gas collapse to form stars, especially stars in the early Universe, when conditions were much different than they are in our own Milky Way. So any new observations, such as these very distant galaxies, helps us to push the bounds of understanding further. It tests our existing hypotheses, and forces us to develop newer and cleverer ideas that can explain what we see and make predictions for the next generation of telescopes to test.

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