Our universe is big enough for billions of galaxies, star assemblies, planets and clouds of dust to dance harmlessly around each other - most of the
Only in crowded galaxy clusters does this dance become more intimate, and it can turn deadly.
We're talking Galactic Cannibalism - the slight tendency of larger galaxies to munch upon the poor little ones!
When a large galaxy approaches a smaller one, its gravitational pull rips the poor tiddler to pieces! Over a few millions years, the attacker reduces
the smaller galaxy to pieces, which it then eats.
So what happens to a galaxy as it gets munched? In the vastness of intergalactic space, head-on collisions are extremly rare. But even a close
encounter can dramatically alter the orbits of planets and stars in the victim galaxy, as they come under the gravitational effects of its attacker's
system. In addition, the interstellar clouds of dust and gas from the two galaxies collide with explosive force. The collisions lead to a rise in
temperature, increasing the pressure in the cannibals galaxy and leading to the formation of new stars and high-speed jets and dust.
How do you spot past episodes of galactic cannibalism, i hear you say?
This is how!
If you know what to look for they are very distinctive, since the new star tends to form a halo around the cannibal galaxy. These young stars are
easily identifiable because they look so blue. A team headed by Eric Peng at Johns Hopkins University in Maryland recently used this blue signature to
identify the remains of a dwarf galaxy that had been swallowed up by the massive galaxy Centaurus A, several million years ago.
Does galactic cannibalism look as spectacular as it sounds?
Yes, i definetly think so!
Here is a link to Hubble's recent photos.
How common is galactic cannibalism? Not as common as it used to be. The universe in its early days was much smaller than it is now, and embryonic star
systems regularly consumed each other. Indeed, it was this primordial cannibalism that drove the evolution of every galaxy.
Does our own galaxy, the Milky Way, show any cannibalistic tendencies? Yes: we are currently munching on our immediate galactic neighbours, the Large
and Small Megellanic Clouds, which we will have fully digested in around 100 million years!
We are also in severe danger of being munched ourselves! Andromeda, a massive galaxy, is heading our way at 300 kilometers a second, and it looks
Andromeda's enormous gravitational pull will tear apart the Milky Way's spiral arms and shred us inside out and stir-fry us for lunch!
There is no point in worrying about this: it won't take place for another two to three billion years, by which time our sun will have long since
burnt out, leaving the Earth a barren wasteland and lifeless.
[Edited on 22-2-2003 by RavenStar]