And Sending Great Images Again!

To celebrate a triumphant comeback from the jaws of Side-A madness, Hubble Space Telescope folk pointed the observatory at a pair of interacting galaxies called Arp 147 that just sort of happen to form what looks  like the number “10” (if you stretch your imagination a little.  This WFPC2 image shows that everything’s in working order and HST’s back to doing science.  Let’s hope it stays working well until the servicing mission can get there to do HST’s long-awaited cosmic makeover.

So, what’s happening in this picture?

The left-most galaxy, or the “one” in this image, is relatively undisturbed apart from a smooth ring of starlight. It appears nearly on edge to our line of sight. The galaxy on the right is the “zero” in this 10. It’s a clumpy, blue ring crammed full of regions where intense star formation is taking place.

The blue ring was most probably formed after the galaxy on the left passed through the galaxy on the right. Just as a pebble thrown into a pond creates an outwardly moving circular wave, the collision and “punch through” of one galaxy through another sent a density wave out from the point of impact. It collided with material in the target galaxy that was moving inward due to the gravitational pull of the two galaxies. The result?  More shocks and clumps of dense gas were produced. This spurred the star formation we see in the galaxy on the right. The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.