Happy 21st birthday, Hubble Space Telescope! On this day, April 20, 1990, On April 24th, 1990, the Space Shuttle Discovery roared into space, carrying HST into orbit and into history. In honor of this anniversary, astronomers have released a new image of the interacting galaxies Arp 273, and it's a beaut:

[Click to galactinate, or grab the cosmic4000 x 4000 pixel version -- and trust me, you want the bigger versions!] Years ago, astronomer Halton Arp observed and cataloged a large number of oddly-shaped galaxies, and we now know these galaxies are interacting gravitationally, and some are colliding. These two galaxies, UGC 1810 (top) and UGC 1813 (bottom) are just such a pair. Collectively called Arp 273, they are in the early stages of a collision. Most spiral galaxies are pretty close to being symmetric and circular, but UGC 1810 is offset and weird. That one arm is thick and sweeps out much farther than the others, making the nucleus of the galaxy decidedly off-center. The string of blue clumps on the top of the galaxy is a sign of furious star formation; massive, hot, blue stars are the culprit, and don't live long, meaning they were born relatively recently. UGC 1813 is distorted as well, with its arms twisted oddly and gas flung every which-way. These two galaxies probably passed very close to each other in the past few million years. The gravity of each galaxy distorted the other, drawing the arms out, slamming gas clouds into each other. Also, the nuclei of both galaxies are unusual: the smaller galaxy's core is very luminous in the infrared, indicating strong star formation obscured by dust, and the bigger galaxy's core is giving off light indicating copious amounts of ionized gas. This is another sign of collision. The gravitational disturbance of this cosmic train wreck has funneled gas into the cores of both galaxies; in the case of the smaller one it has triggered a burst of star formation, and in the bigger one the gas has flowed around the massive black hole at its core, heating up and giving off light (although recent observations of other galaxies have cast some doubt on this idea of collision-fed black holes). While both galaxies are distorted, they still have retained their overall spiral/disk shapes, which indicates this is still early on in their cosmic dance. If they're bound to each other gravitationally the interactions will continue, and most likely will end with the two galaxies merging to become one larger galaxy. It's a common occurrence in the Universe, and our own galaxy may have grown to its large size this way too. Whatever the ultimate fate of these two galaxies, to us, sitting here 300 million light years away from them, they're gorgeous. And it reminds me that while Hubble has done an amazing amount of science over the past 2+ decades, I still think that one of its most important contributions has been to figuratively open the eyes of the public to the beauty and majesty of the cosmos. It's probably the one telescope people can identify by name, and the images it has sent down from orbit have been stunning. I think astronomy is undergoing a renaissance in popular culture, and if that's so, it's due in very large part to Hubble. Happy birthday, Hubble, and may you have many more.

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