Top Ten Astronomy Pictures of 2009

By Phil Plait | December 15, 2009 6:00 am


#10: Pandora’s Galaxy

NGC 4522 is a spiral galaxy that lies 60 million light years away, a denizen of the Virgo Cluster, the nearest such collection of galaxies to our Milky Way.

At that distance, you could wait a million years and not see any motion of the galaxy through the cluster. But don’t be fooled; NGC 4522 is screaming through Virgo at 10 million kilometers per hour. You can see that for yourself: look above it! There is copious gas and dust flowing out of it from the top, as you can easily see in this picture from the Hubble Space Telescope.

As the galaxy slams into the thin gas that exists in the cluster, that material exerts a pressure on the gas and dust inside the galaxy, blowing it out the back. This image of the galaxy shows that material streaming upwards, tendrils of dark dust and red gas flailing behind the galaxy. If you look carefully, you can see patches glowing blue, as new, massive, searingly hot stars are born out of the compressed material.

But I love this picture not just because of that, but also because of the huge number of far more distant galaxies you can see littering the background. Most of them are hundreds of millions of light years away and more, but the illusion of them bursting out of NGC 4522 is fairly strong. Galaxies don’t actually do that, of course, but I rather like the poetic image of babies erupting out of the galaxy like dandelion seeds on the intergalactic wind.

Original Hubble news story

BA Blog post

Gigantic version



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