(Submitted April 16, 2010)
Why do the galexies posses different shapes such as elliptical, spherical,
This is a very interesting question, and still an active area of research.
We do think we have a pretty good understanding, at least at a basic level,
but there's much more to learn in detail.
The main types of galaxies are disk (or spiral) galaxies, elliptical galaxies,
and irregular galaxies. "Irregular" covers pretty much everything that isn't
a spiral or nice ellipse. The short answer is that galaxies form originally
as a spiral disk. As nearby galaxies interact and collide, they eventually
end up as an elliptical shape. So the elliptical galaxies are all much older
Irregular ones are probably the result of galaxies being disrupted by
gravitational interactions with other galaxies.
There is a nice article about galaxies on wikipedia, which has a lot more
We hope that helps.
-Kevin and Hans,
for "Ask an Astrophysicist"