“A house is never still in darkness to those who listen intently; there is a whispering in distant chambers, an unearthly hand presses the snib of the window, the latch rises. Ghosts were created when the first man awoke in the night.” –J. M. Barrie
But off in space, a whopping 320 million light years away, lies the great Coma Cluster, the closest huge cluster of galaxies to us.
Whereas our local group just has two large galaxies in it (our Milky Way and Andromeda), the Coma Cluster has over 1,000. In fact, the two large galaxies at the center of the Coma Cluster are each over one hundred times as massive as either our own galaxy or Andromeda!
But each of these thousand galaxies, should we choose to look at it in extraordinary detail, has its own, rich, and sometimes scary story.
Enter the telescope.
Of all the optical telescopes, only Hubble — from its vantage point in space — has the resolution and exposure time (28 hours!) necessary to resolve a single galaxy at high resolution at this distance.
Here it’s taken a look — at the highest resolution ever — at NGC 4911. What do we see? For once, we get to take a look in true color, exactly as our eyes would see it.
Well, we have a nice looking face-on spiral galaxy here, that’s for sure. (This is the picture Hubble took.) But, like many Hubble images, this one is at a much higher resolution than it appears. Let’s go in for a closer look.
Okay, now we’re getting somewhere. This galaxy has just walked away as the survivor from quite a bit of violence. See the pink spots surrounding its spiral arms?
That’s evidence of star formation, meaning that some major event just happened to trigger it.
Do you also see the huge, extended spiral arms that come out past the edge of the galaxy?
Those don’t happen very often; none of the galaxies in our local group have extended spiral arms like that! So what’s happened here? There are really only two possibilities.
1.) Another galaxy came along, gravitationally disrupted this one, and caused the star formation and the extension of the spiral arms. Of course, in most cases where this happens, we can see the culprit, like M51 (the large spiral above) has its companion, NGC 5195.
2.) This galaxy just won a game of Hungry, Hungry Hippos with a smaller one. The extended arms could be nothing more than galactic cannibalism, although the companion must have been significantly smaller. How do we know? The spiral structure of the main galaxy isn’t nearly disturbed enough.
Keep this in mind: in the Universe, nothing is safe from the pull of gravity. The cycle of creation and destruction continues, even on the scale of a galaxy. In fact, the latter option will be our galaxy’s doom in a few billion years, when Andromeda comes to eat the Milky Way!