Phil Plait has a great post on the latest mind-expanding discovery from the Hubble Space Telescope — what may be the most distant galaxy ever observed, at an awe-inspiring distance of 13.2 billion light years from Earth, formed not long after the Big Bang.

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The galaxy was found in the infrared Hubble Ultra Deep Field, or HUDF, an incredible observation where Hubble pointed at one patch of sky and stared at it for 173,000 seconds: 48 solid hours! After Hubble’s Wide Field Camera 3 observed it, this supposedly blank patch of sky came alive with thousands upon thousands of distant galaxies, and in fact the last record-breaking galaxy was found in the image. The picture here shows the whole HUDF image, with the first picture at the top of this post outlined. Click it to see it in full size, and you’ll start to get an appreciation of just how freaking tough these observations are. The sky is full of faint galaxies!

This new discovery was found using what’s called the dropout technique. It works in a clever way: hot stars inside a galaxy can produce ultraviolet light that can ionize hydrogen, that is, remove the electron from a hydrogen atom. So if there is a cloud of hydrogen atoms between you and a galaxy filled with such hot stars, the UV light you see from that galaxy is absorbed handily by that gas, and you don’t see the galaxy. However, visible light can pass through the gas, so if you use filters to observe the galaxy, you’ll see it in the red filter, the green filter, the blue filter, but then pop! In the UV filter it’s gone. The galaxy has dropped out of sight.