Bang!

Contributed by
Aug 11, 2011
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450 million light years away are two interacting galaxies. Both spirals, they are caught in each other's gravitational claws. Already distorted and bound, eventually, to merge into one larger galaxy in a few million years, the view we have of them from Earth is both amazing and lovely... and hey: they're punctuating their own predicament!

[Click to exclamatenate.]

Looking a lot like an exclamation point, the two galaxies together are called Arp 302 (or VV 340). This image is a combination of pictures from the Chandra X-Ray Observatory (purple) and Hubble (red, green, and blue). The bottom galaxy is a face-on spiral, while the upper one is seen more edge-on, giving the pair their typographical appearance.

They're pretty nifty even if it weren't for the funny coincidence of shape. The upper galaxy has a supermassive black hole in its core that's actively feeding, but is obscured by thick layers of dust -- the abundance of dust is clear in the upper picture, where in optical light it blocks the brighter material behind it (and the warped appearance is a dead giveaway the two galaxies are interacting; the plane of a disk galaxy gets distorted that way when affected by the gravity of another). That dust warms up, making the galaxy boom out infrared. The inset image is a combo of IR (shown in red) from Spitzer and ultraviolet (blue) by Galex, two other orbiting observatories. You can see how the core of the upper galaxy is bright in the IR, but the whole galaxy is strongly emitting, too.

The bottom galaxy, on the other hand, is much brighter in the UV, indicating it has a lot of active star formation, while the upper one doesn't. Clearly, these are very different galaxies. Why? Perhaps they are different ages -- older galaxies tend to have less star formation, so maybe the bottom one is younger. Maybe it simply has more gas in it with which to form stars. It's hard to say. But studying such objects in multiple wavelengths, as was done here, provides critical clues to how they behave and why they do what they do.

Which is all well and good, but I still love how much it's shaped like an exclamation point. Too bad it's not part of the Comma Cluster!

Image credits: X-ray: NASA/CXC/IfA/D. Sanders et al; Optical: NASA/STScI/NRAO/A. Evans et al.; IR/UV: NASA/JPL-Caltech/J.Mazzarella et al.


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