Interacting Galaxies

People around the world voted on nasa.gov to select the next object the Hubble Space Telescope would view, choosing from a list of objects Hubble had never observed before. This was to celebrate the 400th anniversary of Galileo's observations. This program was called “Hubble's Next Discovery -- You Decide”. The last date was March 1st 2009 and the winner from the list is “Interacting Galaxies: Arp 274”. Apr 274 is a pair of interacting galaxies. The winning image of the interacting Galaxies will be released between April 2 and 5.

What are Interacting Galaxies?

Interacting galaxies or Colliding Galaxies are the result of one galaxies gravitational effect on the other. There are different types of interactions between the galaxies depending on their sizes and shapes.

Satellite interaction – Satellite here does not refer to man made satellites (remember, Moon is Earths natural satellite???). A giant galaxy interacting with one of its satellite galaxy is common. Most likely the satellite galaxy due to its gravity distorts the primary galaxies one of the spiral arms. This could result in a small amount of star formation.

Galaxy Collision - When two galaxies collide and do not have enough momentum to continue traveling after the collision, they tend to fall back into each other and eventually merge to form one galaxy. This is called a galaxy collision.

Galactic cannibalism - When a large galaxy, through tidal gravitational interactions with a companion, merges with its companion, resulting in a larger, often irregular galaxy it is called, Galactic cannibalism.

Well, all this is okay… but for people like me who are wondering “Why do galaxies ever collide if they were all ejected from a point (Big Bang) at constant speed?”

That is because they were not ejected from a single point in the Big Bang. This is major mistake non-astronomers make in thinking about the Big Bang. The Big Bang did erupt from a single point in Space but as time passed, small collections of matter began to form and fall under their own strong self-gravity rather than expanding with the rest of the objects in the Universe. Thus the motions in the universe after the Big Bang started to differ became irregular. The largest objects(like very large galaxies) are still sailing along the path of the big bang, but their constituent galaxies may be moving under a local much stronger force of attraction causing them to collide with each other.

Bottom Line: Galaxies follow the Big Bang only on a Large scale and not EVERY scale.