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Credit: NASAESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgement: Davide De Martin and Robert Gendler

Hubble has snapped a spectacular view of M 66, the largest “player” of the Leo Triplet, and a galaxy with an unusual anatomy: it displays asymmetric spiral arms and an apparently displaced core. The peculiar anatomy is most likely caused by the gravitational pull of the other two members of the trio.

Those three galaxies are close enough together that the gravity of each affects the other two. See how the spiral arm at the bottom appears to be wider, messier, less organized than the one near the top of the picture? That’s no illusion. It’s thought that a recent pass by NGC 3628 may have bonked M66 pretty hard, disturbing it and messing around with its structure. The core of the galaxy — usually a smooth and symmetric blob — is all weird and misshapen. The pink glow in the image (emitted by hydrogen gas) is where stars are being born, and the deeper red is where they’re being cranked out en masse. Many times, when a galaxy passes near another one, the gas clouds get all riled up, collapsing to form lots of new stars.

That’s more obvious in the Spitzer Space Telescope image included here. Spitzer sees far-infrared light, which is emitted by warm gas and dust. You can see how wide and weird the lower spiral arm of M66 is, as if it’s been tugged and pulled, like a piece of taffy.

In this Spitzer image, gas and dust emission is also colored red, and starlight is blue (seen as a fuzzy glow since individual stars are not visible). You can see the stars are not distributed evenly: instead there’s more to the right; a good sign that another galaxy is affecting M66. Also, since red is gas and dust, that’s where stars are being actively born, and there’s a lot of that going on just outside the central region of the galaxy. That’s yet another sign that this galaxy was disturbed; the gravity of a passing galaxy can push the gas toward the center where it circles the core and forms stars.

And the clincher? In most galaxies, you see one star exploding at the end of its life every century or so. In the past 20 years, M66 has had three! Hot, massive stars don’t live long, only a few million years. So if a galaxy is making more stars than usual, you’ll see more supernovae than usual. Clearly, M66 has been pretty busy lately!

The unusual spiral galaxy, Messier 66, is located at a distance of about 35 million light-years in the constellation of Leo. Together with Messier 65 and NGC 3628, Messier 66 is the member of the Leo Triplet, a trio of interacting spiral galaxies, part of the larger Messier 66 group. Messier 66 wins in size over its fellow triplets — it is about 100 000 light-years across.

This is a composite of images obtained through the following filters: 814W (near infrared), 555W (green) and H-alpha (showing the glowing of the hydrogen gas). They have been combined so to represent the real colours of the galaxy.