A cluster of galaxies recently observed by three different telescopes now holds the record for the most distant ever seen: 10.2 billion light years, a solid billion light years farther away than the previous record holder!
[Click to embiggen.]
The cluster, called JKCS041 -- evidently all the cool names have already been taken -- was discovered in 2006 and subsequently observed by Chandra. The image above also includes observations by the Very Large Telescope in Chile, and the Digitized Sky Survey. In this image, the blue glow is from X-ray-emitting hot gas between galaxies, and the white galaxies are from the optical and infrared observations.
The image doesn't look like much, but it's scientifically amazing. When light left those galaxies, the Universe was only about 3.5 billion years old! Remember, for a long time the whole cosmos was just gas, and that took a long time to collect, clump up, and form stars and galaxies. It's currently thought that it took a few billion years for clusters of galaxies to form after the Big Bang, so JKCS041 looks like it was an early bloomer. We may find even more distant clusters, but there probably aren't too many more out there, and they almost certainly won't be much farther away than this one.
Clusters are among the largest structures in the Universe (the only things bigger are superclusters; clusters of clusters if you like), so studying them tells us a lot about conditions in the early Universe. And, of course, the farther back we find them the more interesting things get! I suspect that the newly-refurbished Hubble may be pointed this way sometime soon, too, and I also imagine JKCS041 will be a good target for the James Webb Space Telescope, which will be the largest space telescope ever launched. When it's observed by these observatories, what secrets about dark matter, dark energy, and the early Universe will the cluster reveal?
And since I hate ending posts with rhetorical flourishes, I'll take a stab at a generic answer: surprises. Whenever we probe deeper, look farther, the one thing we discover is that the Universe will always have something unexpected up its sleeve. That's one reason science is so much fun! Image credit: X-ray: NASA/CXC/INAF/S.Andreon et al Optical: DSS; ESO/VLT.