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.