Category Archives: galaxy interactions

galaxies, galaxy interactions, hubble space telescope

HST’s Back!

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And Sending Great Images Again!

Interacting galaxies Apr 147
Interacting galaxies Apr 147

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.

galaxies, galaxy interactions

It’s a Galaxy-Eat-Galaxy Universe

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Galactic Cannibalism Rules

We live in a galaxy that used to be several other galaxies that consumed each other to become the Milky Way. In fact, it’s still eating up a dwarf galaxy or two. It turns out that many larger galaxies grew to their current configurations by snacking on each other, amassing size and bulk. If we could watch it happen “in real time” the process of two galaxies out for a munch would look like an animation created by the American Museum of Natural History in New York City. (Check it out!)

These collisions don’t happen overnight, even by cosmic standards. The process begins well before the galaxies even touch each other. This is because the gravitational influences of each galaxy (and associated dark matter components) reach out far beyond the “lit” component (stars, etc.) Those influences start stripping away materials as the galaxies approach, and continue to do so throughout the collision and for a long time afterward.

The whole process can take many hundreds of millions of years, and as I pointed out above, it’s still happening as the Milky Way gobbles up the Sagittarius dwarf galaxy, for example. And, you can look out in the universe and see lots of other places where galaxy cannibalism and merging is taking place.

This Hubble Space Telescope image shows a collision in progress called The Antennae. It shows quite well one aspect of galaxy cannabalism–starbursts. All that colliding material spurs a lot of formation of hot, blue, massive stars — which show up as blue streamers and hotspots.

The Milky Way may be headed for another collision, this time with the Andromeda Galaxy, which lies some 2.5 million light-years away. If it happens, it could really change the appearance of our skies in five billion years’ time. It’s a matter of some conjecture as what effect this will have on planets and life in the galaxy, but by the time this happens, Earth and the Sun will have been long gone. Even a close approach, however, will affect the shapes of both galaxies forever.