And who really couldn't resist an article that uses the word "embiggen". Really.

From the Discover Magazine blog:

Incredibly, even though hundreds of billions of stars are involved, each individual star is far too small to suffer a physical collision. But gas and dust clouds are much bigger than stars (they can be hundreds of trillions of kilometers across, as opposed to stars which are a trifling million or so kilometers in diameter), so collisions between them are common. When clouds collide they collapse and undergo violent bouts of star formation. This too is clear in the image: the blue clumps in the tidal tails are vast regions of clusters of stars being born; over 100 such clusters have been identified in this image in the tail on the right alone.

Collisions like this blast out energy, not just in visible light, but at other wavelengths as well. In infrared alone, NGC 2623 radiates with the power of 400 billion times the Sun’s energy. This makes NGC 2623 a ULIRG: an ultraluminous infrared galaxy. Although relatively rare locally, they are so common at great distance (and therefore earlier on in the age of the Universe) that they comprise as much as half of all the infrared background glow we see in the Universe. The huge amount of infrared comes from the collision itself; star formation produces prodigious amounts of dust which absorb ultraviolet light from newly-born stars and re-radiate it in the infrared. The collision also dumps gas and dust into the central supermassive black holes in the cores of the two colliding galaxies, which piles up in a flat disk outside the black hole, heats up hugely, and again glows brightly.

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Read the full article (with the gorgeous Hubble pic from 2007) here.